Why is carbon dioxide produced in alcohol fermentation but not in lactic acid fermentation?

Why is carbon dioxide produced in alcohol fermentation but not in lactic acid fermentation?

We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

From my understanding, alcohol fermentation takes place in yeast and lactate production takes place in humans.

These two pathways take place only when there is insufficient oxygen, because the other parts of metabolism (TCA cycle, ETC) can't take place as they happen in the mitochondria, which requires O2.

For alcohol fermentation, there is production of carbon dioxide while lactic acid fermentation does not produce carbon dioxide. CO2 is produced when there is an oxidation of one carbon molecule. So my main question is: since there is a lack of O2, how does yeast produces CO2 while humans do not?

Also, how does NAD+ recycle all the time when glycolysis is happening?


Glycolysis needs a steady supply of NAD+ to happen - this is the driver for the anaerobic oxidation to lactate and ethanol, although this is energetically much less favorable than the complete oxidation. But without oxygen there is no other way to keep the glycolysis active for at least some energy supply.

The difference is located in the enzymes available for the conversion of the pyruvate. This is the Lactate dehydrogenase in humans (and other mammals) and the Pyruvate decarboxylase in yeast. The first catalyzes the reaction from Pyruvate to Lactate, the second from Pyruvate to Acetaldehyde and CO2, the Acetaldehyde is subsequently converted to Ethanol. Only the second step produces NAD+.

See the illustration (from here) for further understanding:

The CO2 produced in this reaction does not occur due to oxidation, but is released from the decarboxylation of the Pyruvate. See the illustration below (from here):

In the production of lactate no decarboxylation is happening which allows the backreaction from lactate to pyruvate once enough oxygen is present again.

Industrial Biotechnology and Commodity Products


ABE fermentation, initiated at the beginning of the 20th century, was used to produce the acetone or butanol for production of artificially synthetic rubber, lacquer for mobile industry as well as manufacture cordite during World War I and II. However, in the last half of 20th century, ABE fermentation declined and lost its economic competitiveness with the rapid development of petrochemical industry. Nowadays, the eager for renewable biofuels kindled scientific and commercial interest on the microbial ABE fermentation for producing biobutanol from renewable feedstocks. Butanol as an advanced biofuel has gained great attention due to its environmental benefits and superior properties to ethanol, such as higher energy content, lower water absorption, better blending ability with gasoline, and direct use in conventional combustion engines without modification. However, the cost of butanol production via ABE fermentation by Clostridial such as Clostridium acetobutylicum and Clostridium beijerinckii is not economically competitive, which has hampered its industrial application owing to the poor butanol toxicity and relatively high substrates cost. As the genome sequences of two typical solventogenic bacteria C. acetobutylicum ATCC 824 and C. beijerinckii NCIMB 8052 have been released, the systematic analyses using omics technologies make it possible to gain new insight into the clostridial physiology and regulatory mechanisms. With the developments of genetic manipulation tools and product recovery techniques, the strain performance and downstream process greatly impact the economics of ABE fermentation. This article introduces the basic knowledge about the ABE fermentation and summarizes the current progress.

Discussion & Explanation

The hypothesis was supported in that all forms of sugar produced energy and that glucose was the most efficient.

The carbon dioxide produced can be directly related to the energy produced through fermentation because carbon dioxide is a by-product of ethanol fermentation (Cellular, 54). The control that contained no sugar produced no energy because a source of sugar is required for glycolysis and fermentation to occur.

Glucose had the greatest rate of energy production because its rate of carbon dioxide production was the largest. Sucrose had the second-highest rate of production while fructose had the lowest rate out of the three sugars. Glucose’s rate of energy production was more than three times that of fructose.

Glucose was directly used in the glycolysis cycle and did not require any extra energy to convert it into a usable form (Freeman, 154). This supported why glucose was the most efficient.

Sucrose required an enzyme and energy input to break it down into glucose and fructose in order for it to be processed in glycolysis (Freeman, 189). Fructose also could not be used immediately in the glycolysis chain but had to be altered to enter the chain as one of the intermediates (Berg, 2002).

These processes required to convert the non-glucose sugars into a usable form reduced their efficiency when compared to glucose. The largest source of error for the experiment was the start time of fermentation. The yeast was added to the fructose solution well after the glucose and fructose yeast solutions began fermenting.

Fermentation takes time to reach its maximum rate of energy production so the time gap left glucose and sucrose further ahead than fructose in the fermentation process (Berg, 2002). The data on the rate of carbon dioxide production was therefore skewed because the start of fermentation was not controlled.

Glucose and sucrose appear far more efficient than fructose because of this error. If this experiment were to be repeated, extra care would be taken to ensure that fermentation began at the same time. The measurements of sugars would be measured in equal molarity and not by percent in a solution so that the sugar molecules are equal across all of the tests.

Other follow-up experiments may include testing other types of yeasts to see how fermentation rates are impacted. The results of these experiments could impact what sugars are the most efficient in alcohol fermentation. This could determine what types of sugar brewers should use for the most efficient production of alcohol.

Help Us Fix his Smile with Your Old Essays, It Takes Seconds!

-We are looking for previous essays, labs and assignments that you aced!

Related Posts

Over the last few years, the issue of carbon monoxide (CO) poisoning in the home&hellip

3 Types of Television Production Live Live-to-Tape Pre-Produced Live Television Production Live television production is&hellip

All living things are on Earth are carbon based life forms, carbon is the essential&hellip

The term ecosystem was first used by Tansley (1935) to refer to all the components&hellip

Problem: Yeasts undergo aerobic cell respiration if there is sufficient oxygen and releases carbon dioxide&hellip

Author: William Anderson (Schoolworkhelper Editorial Team)

Tutor and Freelance Writer. Science Teacher and Lover of Essays. Article last reviewed: 2020 | St. Rosemary Institution © 2010-2021 | Creative Commons 4.0

The Science of Sauerkraut: Bacterial Fermentation, Yum!

Last week my husband needed some jars for cooking purposes. Tesco sell jars for somewhere around £3 each. However they also sell large jars full of sauerkraut for £1 each.

Last week my husband needed some jars for cooking purposes. Tesco sell jars for somewhere around ?3 each. However they also sell large jars full of sauerkraut for ?1 each. Which means that last weekend we had an awful lot of sauerkraut to try and get through.

I’m not a great fan of sauerkraut, which is a pity because most of the taste comes from the action of bacteria. Not just one bacteria either, but a whole range of different species are involved in the fermentation process. The bacteria don’t even need to be added to the sauerkraut, as they live naturally on the cabbage leaves. All that is required to start the process off is shredded cabbage and salt.

The first stage of sauerkraut fermentation involves anaerobic bacteria, which is why the shredded cabbage and salt need to be packed in an airtight container. At this stage the surrounding environment is not acidic, just cabbagey. The bacteria, mostly Leuconostoc species, produce carbon dioxide (replacing the last vestiges of oxygen in the jar) and lactic acid, which is a natural byproduct of anaerobic respiration. Eventually, the conditions within the jar become too acidic for these bacteria to survive and they die out, replaced with bacteria that can better handle the acidic conditions such as Lactobacillus species.

The lactobacillus further ferment any sugars remaining in the cabbage, using anaerobic respiration. This produces more lactic acid, until the sauerkraut reaches a pH of about 3. These bacteria are inhibited by high salt concentrations (so most sauerkraut contains around 2-3% salt) and low temperatures, which is why the fermenting jars should be left at room temperature rather than in the fridge. At pH3 the lactobacillus stop fermenting and the sauerkraut can be stored until needed.

All the these bacteria help to create the tangy acidic taste, however there are ways that microbial growth can go wrong. Overgrowth of the lactobacillus, for example if the jar is stored at too high a temperature during fermentation, can cause the sauerkraut to form the wrong consistency. Likewise if the sauerkraut gets too acidic too early the lactobacillus get in on the action early leading to soft sauerkraut. Although the finished sauerkraut is far too acidic for pathogens to live in, fungal spores may settle on the surface and spread, spoiling the food.

Although sauerkraut is a German word, the dish is thought to have originated in China with cabbage fermented in rice wine or brine. This spread to Europe by way of Ghengis Khan’s invaders where the cabbage was dry cured with salt. As sauerkraut keeps for long periods, and is a source of vitamin C, it was favoured by the Dutch sailors, who took it with them when they travelled to America. Captain Cook also travelled with it to Australia, as sauerkraut contains a range of vitamins and minerals that are difficult to obtain when travelling for long periods at sea.

As the bacteria required for sauerkraut fermentation are found on the cabbage leaves, it’s a very easy and healthy dish to produce. All you need is cabbage! By exploiting the actions of bacteria simple ingredients such as cabbage and salty water can be used to produce a healthy dish that can be stored long past the time when raw fruit and vegetables will have begun to spoil.

The views expressed are those of the author(s) and are not necessarily those of Scientific American.


A biochemist with a love of microbiology, the Lab Rat enjoys exploring, reading about and writing about bacteria. Having finally managed to tear herself away from university, she now works for a small company in Cambridge where she turns data into manageable words and awesome graphs.

This research has arisen due to a problem in biology class, which was raised to S. cerevisiae (Yeast) with a substrate of carbohydrates such as maltose with the objective of fermenting this disaccharide, resulting in the production of alcohol. At this time the question came up that if only of maltose yeast could get the energy to survive. It is for this reason that it was thought experience bringing people into contact with the yeast with other carbohydrates.

As already mentioned in the introduction, in the alcoholic fermentation produces CO2 and ethanol. Considering this, in the experimental design is to use a total of four substrates: Glucose, maltose, sucrose, and fructose with the purpose of showing which of these substrates the yeast makes a more efficient energy transformation and produces more Carbon Dioxide. For the above was used as a parameter, the release of CO2considering it proportional to the amount of substrate metabolized by the yeast.

Independent variable: Sugar Type.

Dependent variable: Quantity of CO2 produced in 20 minutes.

Lab Explained: Carbon Dioxide Production by Yeasts under Different Temperatures

Yeasts undergo aerobic cell respiration if there is sufficient oxygen and releases carbon dioxide as a waste product. Yeasts, like any other cells, have an optimum temperature at which they work most efficiently, including the process of cell respiration. This experiment aims to discover the relation between temperature and the carbon dioxide yield of yeasts to discover the optimum temperature for yeasts’ execution of aerobic cell respiration.

It is hypothesized that yeasts carry out aerobic cell respiration most efficiently at high temperatures because high temperature is likely to activate the process at a higher rate. Cells are most active in high temperatures yet within their tolerance of heat, if the temperature exceeds 40 degrees, yeasts, along with their enzymes, will die off or become denatured so they no longer function. On the contrary, low temperature will not activate the yeasts to work as yeasts are not adapted to a cold environment.

  • Independent variable: temperatures of 10% glucose solution in which yeasts are placed to carry out aerobic cell respiration (6°C, room temperature, and 30°C are the temperatures investigated, though the actual room temperature at the lab is noted down)
  • Dependent variable: Change in CO2 concentration after yeasts were placed in the glucose solution over time at different temperatures (CO2 concentration in 3 minutes recorded at an interval of 30 seconds)
  • Constants/controlled variables: concentration of glucose solution (10%), the mass of glucose solution used at each trial (50 gm of water and 5 gm of glucose), the mass of yeasts used at each trial (250 mg), rate of stirring of the solution on the stirring plate (500 rpm), time to record CO2 concentration after yeasts are put in (30 seconds, 1 minute, 90 seconds, 2 minutes, 150 seconds, 3 minutes), chemicals used (10% glucose solution), apparatus and equipment (test tubes, 100 ml beakers, 50 ml graduated cylinders with an uncertainty of ±0.1 ml, 250 ml Erlenmeyer flasks, balance in g accurate to 2 decimal places, a hot plate that also contains a magnetic stirrer plate and magnetic stirring bar, thermometer range from 0°C to 100°C with an uncertainty of ±0.01°C, CO2 sensor which connects to an Xplorer GLX machine, test tube racks, timer accurate to 0.01 s, 1 spatula, 1 ice bath consists of a 50 ml beaker and ice cubes, 1 fridge)
  • Yeasts 1.5 g
  • Glucose 30 g
  • 500 ml distilled water
  • 4 100 ml beakers, uncertainty ±5 ml
  • 1 thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C
  • 12 test tubes
  • 1 test tube rack that can hold 12 test tubes
  • 1 50 ml graduated cylinder with an uncertainty of ±0.1 ml
  • 6 250 ml Erlenmeyer flasks, uncertainty is not concerned as they are not used to measure volumes
  • 1 Weighing balance in g accurate to 2 decimal places
  • 1 spatula
  • 1 hot plate that also contains a magnetic stirrer plate
  • 1 magnetic stirring bar
  • 1 CO2 sensor charged to the full battery with a stopper binds to the flask
  • 1 GLX machine with a full battery
  • 1 timer accurate to 0.01 s
  • 1 ice bath, including 1 50 ml beaker and 6 ice cubes with a side length of approximately 1 centimeter
  • 1 fridge with a refrigerator compartment that refrigerates at a temperature higher than 0°C, approximately 0 to 4°C

6 °C glucose solution preparation:

  1. 100 ml beaker is filled with distilled water
  2. 6 ice cubes with side length of approximately 1 centimeter are placed in the 100 ml beaker with distilled water
  3. The 100 ml beaker is laid aside in the refrigerator compartment with a temperature ranged from 0°C to 4°C but higher than 0°C so water will not freeze in the fridge overnight
  4. On the second day, 5 g of glucose is weighed on a weighing balance accurate to 2 decimal places
  5. 5 g glucose is put into a test tube and placed on the test tube rack
  6. Similarly, 0.25 grams of yeasts are measured by a weighing balance accurate to 2 decimal places and transferred into a test tube, which is placed on the test tube rack
  7. The 100 ml beaker stored in the fridge is taken out and poured into a 50 ml graduated cylinder with an uncertainty of ±0.1 ml to measure 50 ml of ice water, ice cubes will stay in the beaker
  8. 50 ml ice water is poured into the 250 ml Erlenmeyer flask
  9. The Erlenmeyer flask is placed on a hot plate which also functions as a magnetic stirring plate and a magnetic stirring bar is put into the flask
  10. 5 gram of glucose already measured in the test tube is poured into the water
  11. The stirring plate is turned on, stirring at a rate of 500 rpm
  12. The stirring plate is turned off once glucose is fully dissolved
  13. A thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C is inserted into the glucose solution, at this stage, the ice water is warmed up, the procedure cannot be proceed until the temperature of the solution reaches 6°C
  14. The CO2 sensor is connected to the GLX machine which displays the CO2 concentration in the air
  15. The CO2 sensor, which attached to a stopper that binds to the neck of the flask to block the flow of air, is embedded into the flask
  16. The CO2 concentration will be displayed on the GLX machine and is noted as the original CO2 concentration in the flask
  17. The CO2 sensor is pulled out and yeasts in the test tube are poured into the flask, CO2 sensor is put back into the flask, the magnetic stirring plate is turned on at a revolution rate of 500 rpm, the stopwatch is ticked off, all this should be done without intervals
  18. The CO2 concentration in the flask is recorded every 30 seconds for 3 minutes so 6 numbers will be recorded
  19. The procedure above is repeated twice more

Room temperature glucose solution preparation:

  1. 100 ml beaker is filled with distilled water
  2. The beaker is placed in the lab overnight
  3. On the second day, 5 g of glucose is weighed on a weighing balance accurate to 2 decimal places
  4. 5 g glucose is put into a test tube and placed on the test tube rack
  5. 25 grams of yeasts are weighed on a balance accurate to 2 decimal places
  6. 25 g yeasts are transferred to a test tube and placed on the test tube rack
  7. The distilled water in the 100 ml beaker is poured into a 50 ml graduated cylinder with an uncertainty of ±1 ml to measure 50 ml of water at room temperature
  8. 50 ml water is poured into the 250 ml Erlenmeyer flask
  9. The Erlenmeyer flask is placed on a hot plate which also functions as a magnetic stirring plate and a magnetic stirring bar is put into the flask
  10. 5 grams of glucose already measured in the test tube is poured into the water
  11. The stirring plate is turned on, stirring at a rate of 500 rpm
  12. The stirring plate is turned off once glucose is fully dissolved
  13. A thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C is inserted into the glucose solution, the temperature measured should be the room temperature and is noted for further examination
  14. Steps 14 to 19 in 6°C glucose solution preparation from the last section are repeated

30°C glucose solution preparation

  1. 50 ml distilled water is measured with 50 ml graduated cylinder with an uncertainty of ±0.1 ml
  2. 50 distilled water is transferred to the 250 ml Erlenmeyer flask
  3. 5 g of glucose is weighed on a weighing balance accurate to 2 decimal places
  4. 5 g glucose is put into a test tube and placed on the test tube rack
  5. 25 g of yeasts are measured by a weighing balance accurate to 2 decimal places
  6. The yeasts are put into a test tube and placed on the test tube rack
  7. 5 gram of glucose already measured in the test tube is poured into the water in the flask
  8. The flask is placed on the top of a hot plate that also functions at a magnetic stirring plate, which is set to 30 degrees and turned on the stirring at a rate of 500 rpm
  9. The stirring plate is turned off once glucose is fully dissolved
  10. A thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C is inserted into the glucose solution to monitor the change in temperature
  11. Once the temperature reaches 30°C, the thermometer is taken out, hot plate turned off
  12. Steps 14 to 19 in 6°C glucose solution preparation from the second last section are repeated

Methods of control of variables:

The independent variables are temperatures of 10% glucose solution in which yeasts are placed to carry out aerobic cell respiration. They are 6°C, room temperature, and 30°C respectively.

The methods of how to manipulate the independent variables are explained in the procedure. Briefly, 6°C glucose solution needs to have a distilled water stored in an ice bath and placed in the refrigerator compartment of a fridge. Note that it cannot be put into the freezer compartment, otherwise the distilled water will be frozen so cannot be used. Overnight, the temperature will be close to the temperature of the refrigerator compartment, which should be between 0 to 4°C.

The water will be taken out the second day and its temperature is measured with a thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C. The temperature is likely to rise during the process, so once the temperature reaches 6°C, the rest of the procedure can be carried out. The room temperature glucose solution requires a similar setup as the 6°C solution. Distilled water fills the 100ml beaker and is placed in the lab overnight to require water at room temperature.

The exact temperature, however, should be noted for quantitative analysis. The 30°C glucose solution requires a hot plate. Distilled water is heat up on the hot plate set at 30°C and a thermometer is inserted into the flask with distilled water to monitor change in temperature. Once the temperature reaches 30°C, the hot plate is turned off and the rest of the procedure must be carried out immediately so that the water or the glucose solution does not cool down.

The dependent variable is the change in CO2 concentration after yeasts were placed in the glucose solution over time at different temperatures. One would record the initial CO2 concentration of the glucose solution before yeasts were put in to obtain the stock concentration of CO2 in the flask. Then, the CO2 concentration in the flask is recorded at a 30 seconds interval after yeasts are put in for 3 minutes, so after 30 seconds, 1 minute, 90 seconds, 2 minutes, 150 seconds, and 3 minutes the CO­2 concentration are recorded. One would need a timer for this.

The experimenter may wish the record the data and graph them in a graph of CO2 concentration in the flask over time. With the graph, one would subtract the initial CO2 concentration from the CO­2 concentration, the CO­2 concentration at 30 seconds from the CO2 concentration at 1 minute and so on the obtain the difference of CO2 concentration between each interval to monitor the overall rate of change in CO2 concentration at different temperatures in which yeasts carry out aerobic cell respiration.

One controlled variable is the concentration of glucose solution, which is kept at 10% by measuring 5 grams of glucose with a weighing balance accurate to 2 decimal places and then the glucose is poured into a 50 ml distilled water measured by a 50 ml graduated cylinder with an uncertainty of ±0.1 ml, mixed by the magnetic stirring plate and bar. This process is carried out in all three temperatures.

Another constant is the mass of glucose solution used at each trial. Similar to the previous one, 50 gm of distilled water are measured by a 50 ml graduated cylinder and 5 gm of glucose are weighed by a weighing balance. They will be mixed using a magnetic stirring plate and a magnetic stirring bar put into the Erlenmeyer flask that contains the distilled water and glucose.

Note that the glucose can be stored in a test tube and put aside and when being poured into the flask containing distilled water, the test tube is knocked lightly to ensure glucose would not stick to the internal surface of the test tube so most if not all 5 gm of glucose will go into the flask.

The mass of yeasts used at each trial – 250 mg – is another controlled variable. Like glucose, yeasts are also measured with a weighing balance accurate to 2 decimal places in grams. Weighing yeasts and transferring them into a test tube can be tricky, extra concentration is required.

The rate of stirring of the solution on the stirring plate is 500 revolutions per minute. The indicator should be switched to 500 rpm with the magnetic bar placed inside the solution and with yeasts, if numbers of rpm are not shown, the revolution rate is switched to medium instead.

Another constant is the time to record CO concentration after yeasts are put in. The time is 30 seconds, 1 minute, 90 seconds, 2 minutes, 150 seconds, 3 minutes. A stopwatch or a timer is required and also accurate to 0.01 s. At these 30 seconds intervals, the CO­2 concentration is displayed on the GLX machine connected to the CO2 sensor, the number is jogged down by looking at the number displayed in ppm.

The chemicals used, i.e. 10% glucose solution, is another controlled variable.

Remember only glucose, not other sugars, are investigated in this experiment. The apparatus and equipment used are constants as well. They are 12 test tubes, 100 ml beakers, 50 ml graduated cylinders with an uncertainty of ±0.1 ml, 250 ml Erlenmeyer flasks, balance in g accurate to 2 decimal places, a hot plate that also contains a magnetic stirrer plate and magnetic stirring bar, thermometer range from 0°C to 100°C with an uncertainty of ±0.01°C, CO2 sensor which connects to an Xplorer GLX machine, test tube racks, timer accurate to 0.01 s, 1 spatula, 1 ice bath consists of a 50 ml beaker and ice cubes, 1 fridge.

Carbonation in Sour Beers

I recently attended one of my favorite annual sour beer events, Cantillon Zwanze Day. Zwanze Day, which is held every fall, is a day to celebrate traditional Belgian lambics and the products of the Cantillon brewery. Each year, Cantillon releases a different unique beer for the event that is tapped at the same time at all of the locations worldwide. As we have for the past several years, my partner and I traveled to the closest location hosting the event, Monk’s Cafe in Philadelphia, and had a wonderful day enjoying their Belgian style cuisine and a fantastic assortment of draft Cantillon and other great sour beers. One of the beers I drank on draft was Cantillon Rosé de Gambrinus, which I have had the opportunity to enjoy in both draft and bottled versions a number of times over the years. In both draft and bottle, I have noticed that different levels of carbonation can significantly alter the way I both perceive and enjoy this beer. These thoughts prompted me to discuss carbonation levels in sour beer from both a brewer’s and a consumer’s standpoint.

The Basics – What is Carbonation?

Carbon dioxide, a simple molecule composed of one carbon atom and two oxygen atoms, is a natural byproduct of a wide number of chemical reactions that break down more complex carbon compounds. In the case of sour beer production, these carbon compounds are the simple sugars present in wort and the chemical reactions are the alcohol producing fermentations of yeast species such as Saccharomyces and Brettanomyces as well as certain (heterofermentative) strains of the bacteria Lactobacillus.

For the serious chemistry geeks..

For such a relatively simple molecule, the chemistry of carbon dioxide can be very complex. However, for our discussion, we are only going to focus on one important piece of this chemistry: When carbon dioxide dissolves into water, one molecule of carbon dioxide can combine with one molecule of water to produce carbonic acid. The formation of carbonic acid is the reason why carbon dioxide does more for a beer than simply make it bubbly. Carbonic acid lowers a beer’s pH and carries with it the flavor effects that other acids in beer also carry. Keep in mind that carbonation will not change a beer’s pH drastically enough to make it sour. Carbonation can, however, accentuate a beer’s existing sourness on the palate.

In terms of its flavor effects on beer, all carbon dioxide is created equally. This is true regardless of whether the carbonation is created naturally through fermentation or added to a beer in pressurized vessels. That being said, the process of bottle or keg conditioning can produce subtle yet notable changes in flavor due to effects experienced by both Saccharomyces and Brettanomyces when fermenting under pressure. Keep in mind that these effects are subtle and strain dependent. Typically, when we notice a difference in character between a sour or farmhouse ale that was bottle conditioned versus force carbonated, the difference is simply due to a higher level of carbonation in the bottle conditioned version.

Carbonation Levels and Their Effects

For every classic beer style, there will be a general range of carbonation levels that are considered appropriate for that style. These levels, measured in volumes of CO2, developed organically for each style based both upon what tastes best for that beer as well as upon what fermentation and serving methods evolved historically. For example, many British beers would traditionally be served out of wooden casks (a low pressure vessel) and, in turn, these tend to be the least carbonated styles, ranging from 0.75 to 1.5 volumes of CO2. At the other end of the spectrum, and of more interest to sour beer fans, Belgian Gueuze did not exist as a style until glass bottles capable of holding champagne levels of CO2 became modestly available. Gueuze, by definition, is a bottle conditioned style and therefore became commonly served at higher pressures which these new containers were capable of holding, 3.0 to 4.5 volumes of CO2.

This begs the question: Historic conventions aside, would a British Mild taste good at high carbonation and a Gueuze taste good at low carbonation? The answer: Well… It depends. Despite the fact that much of we consider to be “good taste” is personal, there are attributes of any beer that can be made more or less impactful through higher or lower carbonation levels. Lower carbonation levels tend to emphasize the sweet malty flavors in a beer. They also tend to produce a smoother, potentially creamier, finish. Higher levels of carbonation tend to downplay malt sweetness while enhancing both the perception of bitterness and/or acidity in a beer. They also drive more aromatic compounds out of the beer (enhancing aroma) and tend to leave the finish feeling dryer and more crisp. In the case of a British Mild, a low alcohol beer with rich malt flavors and a subtle roast character, too much carbonation can leave the beer feeling thin on the palate, with less sweetness and a more astringent roasted quality. On the other hand, an under-carbonated Gueuze can taste sweeter than intended, while coming across as lackluster in the aroma department.

Additionally for Gueuze and other traditional lambics, I feel that lower levels of carbonation can accentuate the perception of their acetic acid and ethyl acetate components. These chemicals are present to at least some degree in all traditional lambics, but can be perceived as off-flavors if their levels are too high or if other elements of the beer are left unable to balance them. When properly balanced by lactic, malic, and carbonic acids, acetic acid will give a sour beer a round, complex, salivation producing acidity. If unbalanced, acetic acid can taste like vinegar, be harsh, or even burning in the throat. Ethyl acetate at low levels will smell like pears and provide a sharpening edge to a beer, while at higher levels this chemical will smell solventy, like nail polish remover. Traditional lambic brewers and blenders have the skill to optimize the levels of both of these components in their Gueuze and fruit lambics. Therefore, the level of carbonation and equivalently carbonic acid in the finished product can tip the scales in one direction or the other when it comes to perceiving these chemicals.

Carbonation from a Brewer’s Perspective

As a brewer, I want to provide my drinking audience with a beer that has at least enough carbonation to showcase its flavors and aromas in the best possible way. For my palate, this means erring slightly on the high side of the carbonation spectrum for the individual styles of sour beer that I produce.

When sampling base beers or testing out a blend, I am a big fan of using a simple set of tools that allow a brewer to quickly cool and carbonate a sample before tasting. This setup uses a plastic cap which screws onto most standard water or soda / pop bottles and connects to a ball lock gas fitting. With this low cost tool, we can taste small samples of a beer as they will taste when finished with carbonation. As mentioned earlier, carbonation can dramatically alter our perception of flavor and aroma when tasting a beer. Therefore I find it incredibly useful to be able to taste small carbonated samples without having to commit an entire batch to keg or bottle.

As a homebrewer who serves most of my beer on draft, hitting a desired carbonation level is a fairly straightforward process. When a blend is ready, I will transfer the beer to a keg and force carbonate it to the desired level. If bottling, I use counter pressure filling to ensure that every bottle I produce will have about the same carbonation level as the beer that I am tasting on draft. As a homebrewer, these processes are simple and effective, but have a few limitations. First, they are more expensive than bottle conditioning, requiring more equipment. Second, they may be difficult to scale up for professional breweries, as pressurized bottling or canning lines are very expensive and present unique sanitation challenges when working with Brettanomyces and bacteria. Third, the higher the desired carbonation level, the more challenging it is to dial-in handheld or automated counter-pressure bottle fillers. At CO2 volumes above 3.0, excessive foaming and associated low bottle fills and/or excessive wasting of product can easily occur.

At face value, bottle conditioning is a simpler overall process than force carbonation and allows a brewer to target higher levels of carbonation than are practical with other methods. Additionally, bottle conditioning requires less investment in equipment. Unfortunately, bottle conditioning can be less predictable and comes with its own unique set of challenges when dealing with mixed microbe fermentations. The bottle conditioning process for “clean” Saccharomyces-only beers is relatively straightforward and is calculated from a few basic pieces of information including:

  • The amount of CO2 dissolved in a beer after fermentation.
  • The potential residual fermentability of the beer.
  • The desired volumes of CO2.

The inherent difficulty and potential unpredictability of bottle conditioning sour beers arises from three potential issues that need to be dealt with:

  • Long aging times can make our estimates of dissolved CO2 inaccurate.
  • Unless a recipe has been brewed and aged several times using the same strains of microbes, it’s residual fermentability could be nearly impossible to guess. Many strains of Brettanomyces can be hyperattenuative, continuing to slowly ferment the complex residual carbohydrates for months or even years after the primary fermentation is complete.
  • Aggressive strains of Lactobacillus or Pediococcus can convert some portion of simple priming sugar into lactic acid, a process which will not produce any additional carbon dioxide.

A certain amount of unpredictability will always exist when bottle conditioning sour beers. Luckily, these styles do taste great within a wide range of potential carbonation levels and there are some best practices that can help us hit those numbers:

  • When calculating the amount of residual CO2 in your beer, use the highest temperature that the beer reached during its aging period. If a beer was barrel aged, Michael Tonsmeire recommends halving the CO2 estimate. Check out his Priming Sugar Spreadsheet on The Mad Fermentationist Blog.
  • When bottling a beer with Brettanomyces, closely track the beer’s attenuation during its aging. I would recommend against bottling any beer with a specific gravity of 1.008 or less that has not had a stable attenuation for at least 3 months. If a beer has a specific gravity higher than 1.008, I would recommend observing a stable gravity for 6 months before bottling. The only time I would consider bottling younger is if you have brewed the exact beer previously and have a clear expectation of what the final gravity will be. Remember that this practice also applies to counter-pressure filled bottles. Unexpected rises in attenuation can lead to over-carbonation in these beers as well.
  • When bottling a mixed microbe beer, do not introduce new yeast or bacteria strains at the time of bottling. If adding fresh Saccharomyces or Brettanomyces, make sure to use strains that already exist within the beer. Select bottles that can tolerate higher than expected carbonation pressures. No brewer wants to release beers that gush when opened, but it is a far better accident than bottles that explode. If your beer does continue to attenuate after bottling, it will gain approximately 0.5 volumes of CO2 for every point of specific gravity lost. For example: If a beer is bottled at 1.008 SG, and it drops to1.000 SG, it will gain 4 unintended volumes of CO2 in addition to whatever carbonation was provided by priming sugar. Such unexpected attenuation would put the total carbonation of the beer to between 6-7 volumes. Champagne bottles are the only glass containers on the market that can handle these pressures without exploding.

Luckily, it’s rare for any beer which has had a stable gravity over several months to later ferment to 100% apparent attenuation after bottling. While it may be rare, it is however possible, and this has led many professional sour brewers to avoid bottling any beer with a final gravity higher than 1.008 (2 Plato).

For references on performing the actual calculations needed to bottle condition your beers, check out these resources:

Like any brewing process, repetition and experience with your recipes, strains, and fermentations will help take the guesswork out of proper carbonation. I personally err on the side of slighter higher carbonation levels because, as we will see, from a consumer’s standpoint, it’s relatively simple to remove a little extra carbonation from a beer but it is practically impossible for the drinker to add more CO2 to a flat beer.

Carbonation from a Consumer’s Perspective

As sour beer drinkers, we will encounter beers that range from completely still (intentionally or unintentionally uncarbonated) to those with such high carbonation levels that the beers may gush a little (or a lot) upon opening.

When I am trying a new sour beer for the first time, I always open the beer with the assumption that it may be slightly over-carbonated. Regardless of how a beer has been cellared, I prefer to put my sour beers upright into a refrigerator for at least a few days (but more frequently for several weeks) before opening them to allow for yeast and other sediment to settle to the bottom of the bottle and for any carbonation that may have been agitated out of solution by transport to stabilize. When I open a bottle, I like to do so with enough glasses to serve the beer ready to go. If a beer does begin to foam up once opened, having several glasses available can keep from losing beer to spillage that may have been perfectly delicious to drink. Unlike “clean” styles, which generally become very unappealing if they become over carbonated via hyperattenuative wild yeast strains, sour beers tend not to suffer a dramatic drop in flavor quality if they become over-carbonated.

This bottle of Oud Beersel’s Oude Kriek Vieille is an example of a beer that I may consider degassing.

Some sour beers may be purposefully carbonated to the higher end of the range for their styles. It is quite common to find Gueuzes, Fruit Lambics, and Farmhouse Ales with carbonation levels ranging from 3.5 to 4.5 volumes of CO2. While these beers may not gush upon opening, their very high levels of carbonation, in my opinion, can make it difficult to taste the wide variety of other more subtle characteristics in the beer. Beers such as this may benefit from the drinker actually allowing some of the carbonation to escape the beer before consumption. My rule of thumb in regards to this goes as follows:

  • If I pour a beer into my glass that seems to be very highly carbonated (creates a large volume of head with a moderately gentle pour and continues to bubble strongly), I will slowly take a sip of it into my mouth and hold it there.
  • Once in my mouth I will feel how the beer is reacting on my tongue. If the beer feels so spritzy / prickly in my mouth that I’m not actually able to taste much beyond the sensation of carbonation, then I may consider removing some of the extra CO2 from the beer. The best way that I can describe this sensation is to say that if feels like more gas bubbles are hitting your taste buds than actual liquid.
  • The easiest way to remove some extra CO2 from a beer is to pour it gently once or twice from one glass to another, this will release additional carbonation in the form of head with each pour.
  • A second way to degas a highly carbonated beer is to pour it into a decanter and allow it to rest and open up over a period of 10 to 20 minutes. This is very similar to a process used to open up certain varieties of wine and can be done using the same containers. Lambics from the brewery Drie Fonteinen are a classic example of beers that often benefit from some degassing. Their master blender Armand Debelder highly recommends it and I can attest that doing so does bring out a wide range of complex flavors in his blends that may be otherwise missed.

Drie Fonteinen’s Golden Doesjel is an example of a lambic beer served intentionally still.

On the other end of the spectrum exist a wide number of sour beers which are purposely bottled still or with very low carbonation. This is the norm for unblended Lambic and is also often the case for certain single barrel American sour releases. In my opinion, the best way to serve these beers is at the high end of cellar temperature, 55 to 60 F. To help drive aromatics, I will give these beers a vigorous pour and often drink them a little more slowly, allowing some oxygen to gradually mix into the beer. It is interesting to see how these still varietals will open up and change in character over the course of 30 to 60 minutes.

Ending Thoughts

From a brewer’s perspective, sour beers generally undergo complex fermentations with a variety of microorganisms. In some cases the exact organisms involved may be unknown. While we can make educated guesses which tend to become more accurate with experience brewing and fermenting a particular recipe, miscalculations do occur. In fact, they occur rather frequently. This fact leads to a wide variability between the carbonation levels of different sour beers, and even between different batches of the same sour beer. To compound the matter, safety and the prevention of exploding bottles is a very real concern on the minds of sour brewers who distribute their products. That being said, carbonation doesn’t have to be a total shot in the dark. The keys to success in hitting a desired carbonation level are patience, accuracy in measurements, and detailed note taking for future repeatability.

From a consumer’s perspective, we are sometimes disappointed by sour beers that may have a lower or higher amount of carbonation than expected. Fortunately, most sour beers have redeeming flavors at a wide range of carbonation levels. Additionally, there are methods that we as drinkers can use to maximize our enjoyment of these beers.

Hopefully this article has provided both an understanding of the complexities of carbon dioxide in relation to sour beers as well as some practical tips for both the brewers and consumers who love these styles. As always, I welcome your thoughts and questions on the topic!

Matt “Dr. Lambic” Miller

Okay.. Technically its not “impossible” for the consumer to add their own carbonation.. but you’ve got to be a nutcase like your’s truly to bother doing so! Cheers Sour Fans!

Goodwin, Jay, and Scott Moskowitz. “The Sour Hour / Episode 4.” The Sour Hour. The Brewing Network. Concord, CA, 20 Nov. 2014. Radio. (Troy Casey of Casey Brewing & Blending discusses bottle conditioning)

Palmer, John J. How to Brew: Everything You Need to Know to Brew Beer Right the First Time. Boulder, CO: Brewers Publications, 2006. Print.

Steen, Jef Van Den. Geuze & Kriek: The Secret of Lambic. Tielt, Belgium: Lannoo, 2011. Print.

Tonsmeire, Michael. American Sour Beers: Innovative Techniques for Mixed Fermentations. Boulder, CO: Brewers Publications, 2014. Print.

What Are the Waste Products of Respiration?

In animals, such as humans, the waste products of aerobic respiration are water and carbon dioxide, and the waste product of anaerobic respiration is lactic acid. Aerobic respiration is a series of reactions that sees oxygen being consumed in order to release energy from glucose. Anaerobic respiration occurs when there is an oxygen debt in cells.

Aerobic respiration happens mostly within the mitochondria in eukaryotic cells and the energy found in these cells is in the form of adenosine triphosphate (ATP). Respiration is essentially a production process for ATP. During the process, glucose goes through glycolysis, which creates pyruvate and ATP. If there is oxygen available, this pyruvate is oxygenated, creating acetyl-CoA, and moved on to the mitochondrion where more ATP is produced and both water and carbon dioxide are given. Both the water and the carbon dioxide combine to make carbolic acid, which helps maintain the blood's pH levels.

If there is no oxygen available to the pyruvate after glycolysis, the pyruvate enters a process of fermentation. This is known as anaerobic respiration, and it is used when muscle cells have exhausted their oxygen supply. During aerobic respiration, up to 38 ATP can be produced however, in anaerobic respiration, only two are produced. When oxygen is available again, NAD+ in the cell forms with the hydrogen in lactic acid to form more ATP.

Why is carbon dioxide produced in alcohol fermentation but not in lactic acid fermentation? - Biology

Have you ever wondered about how small germs are?
And what are germs anyway?
Are you always being told to wash your hands? Do you know why?

The tiny things you know of as germs are known as bacteria by scientists. They are very small and you can't see them. Many thousands could fit on a pin head. They are alive, in the same way that you are, or a dog is, or a
plant is. The study of these and other small living things or organisms is called Microbiology.

What is a microbiology?

Micro means very small and biology is the study of living things, so microbiology is the study of very small living things normally too small tobe seen with the naked eye.

Activity Using Microscopes

What sort of small, living things do microbiologists study?

First we need to understand the classification of all living organisms. We also need to understand the fundamental characteristics of different types of organisms. As outlined in the classification, microbiology includes the study of:

bacteria (or Eubacteria ) fungi (or Archaeobacteria )
protists archaea algae However, there are other organisms that are studied by microbiologists and these cannot be classified as living by the conventional definitions.

No. It is true that some microbes cause disease and others cause decay and damage to inanimate objects, but without microbes we would not be able to exist. Microbes are everywhere and the more we look the more we find, sometimes in the most unlikely of places.

Our body is infested with microorganisms and most of them are essential for our survival. They assist in food digestion in our digestive system, for instance.

Even microbes that cause decay are useful for they breakdown dead matter into simple chemicals, so the matter can be recycled and used by other - probably more complex - life forms. Without the decay process, the world would soon be covered in dead creatures and plants.

Microbes have different functions for different purposes and to occupy different niches in the biology of the planet. They have evolved when and where they had the opportunity, without any moral imperative. But as humans, we find that some are useful to us and others are dangerous to us. So we view them as either good or bad.

"Good" microorganisms include those that are necessary to maintain our environment, in a way that will support our existence. Then there are our very own microorganisms that our body uses as part of its internal defense system, to fight infection from outside.

"Bad" microorganisms enter the body in a number of different ways, but most commonly by the respiratory and digestive system, or by damaged skin. They cause problems to the body because they destroy body tissue and release toxic substances. This upsets the normal running of the body, which has to divert energy to its internal defense system in order to fight the invader.

Microorganisms that cause disease include:

Firstly, it should be understood that all living things "work" in the same way at the most basic level. There are certain structures and functions that are common to all living organisms. Likewise all living things use similar chemical processes to work - this is known as organic chemistry. One chemical element above all others dominates organic chemistry - carbon. This has some unique properties that allow trillions of different chemicals to be made from a few chemical elements. An account of why carbon is the basis of life is shown here.

Lets us look at some of the key structural and chemical components of living organisms in general and microbes in particular.

The Cell
All living organisms are made from cells . They are the basic unit from which living things are constructed and the smallest part of an animal or plant that can function independently. All cells have an outer coat or membrane that is resilient to the external environment. It is tough and resists damage to the cell, physically, chemically and biologically. It also provides a good internal environment with a boundary where life processes can be performed by the organic chemicals inside the cell. The boundary is important, too, because that stops the contents of the cell from being dispersed.

Prokaryote cells lack a nucleus, and consist of a cell membrane in which several distinct components function. Typically these are:

Chromosomes - A coiled strand of DNA
Ribosomes - Factory-like elements of a cell, where messenger RNA is turned into proteins - building blocks and enzymes - the cell needs
Cytoplasm - The general cell contents
Glycogen granules - to provide energy

Prokaryotes often also possess flagella, which help them move.

Eukaryote cells have additional internal components, notably a nucleus and mitochondria.

Chloroplast Mitochondria
© 1999 The Centre for Microscopy and Microanalysis

Enzymes are organic catalysts which speed-up an organism's chemical reactions, without changing themselves. Chemical reactions can often be speeded up by heating, but in the case of living organisms this can damage them. The enzyme, which is usually protein with a specific shape for each purpose, controls the chemical reactions in the cell and thus allows the organism to metabolize.

There are two groups of enzymes: intracellular and extracellular. The former exist inside cells, controlling the metabolic rate. The latter are produced by cells, but work outside of these. For instance, digestive enzymes are used by the body to break down food in the digestive system.

Enzymes speed up reactions, without being destroyed by the reaction itself. They will not work in high temperatures, or at the wrong pH balance. Each enzyme has a specific function, but it can work in either direction of the chemical reaction.

DNA , deoxyribonucleic acid, is a complex molecule containing instructions for all the functions of the cells of an organism, its "genetic information". It replicates itself by separating its two interwoven strands (the helix) like a zip fastener and attracting free nucleotides (simpler molecules of nucleic acid) in the same order as the original.

The DNA molecule is a double helix made of four types of nucleotide. These are aligned in a ladder formation, which is twisted like a screw. On opposite sides of the double helix are companion nucleotides. Adenine (A) and Thymine (T) are always located opposite other, and so are Guanine (G) and Cytosine (C) . So, each strand of the double helix is a "mirror image" of the other. This is why A, T, G and C are the four letters associated with the genetic code.

DNA is the "master copy" for all the instructions for the cells of the organism.

The image shows the double helix structure of the DNA, which consists of two strands with the cross links at intervals joined be hydrogen bonds. There are ten crosslinks for every complete twist of the double strand. The lower image shows a section of the DNA helix, untwisted. It shows the main components of the strand: Sugars (pentagonal shapes), phosphates (spheres) and organic bases (A, C, G and T).

To replicate, the DNA unzips along the center of the rungs of the ladder. The exposed free ends can then form two new DNA strands by allowing "partner" molecules to link at the exposed rungs. A can only pair with T, and C with G.

RNA , ribonucleic acid, is a much smaller molecule than DNA, which copies the information and takes part in the process of protein synthesis in cells. It differs from DNA in that Uracil (U) replaces Thymine. Unlike DNA it can interact with other molecules, specifically ribosomes. The RNA copy of the DNA information is transcribed from the DNA template, this is known as transcription RNA, this is the copied message of the DNA.

mRNA , messenger RNA, is a further copy of the RNA transcript which has been spliced and modified. It carries the information from the DNA which specifies an amino acid sequence of proteins. In a eukaryote it then moves out of the nucleus into the cytoplasm, where it attaches to the ribosome. In a prokaryote, which does not have a nucleus wall, the next process takes place on-site. mRNA is the new message of instructions from the DNA.

tRNA , transfer RNA, is the adapter molecule which allows the mRNA nucleotide sequences to be translated into protein amino acid sequences. The tRNA anticodons link up to their corresponding codons of the mRNA, one at a time, as the mRNA moves through the ribosome. This is translation . tRNA is the receiver of the message.

rRNA , ribosomal RNA, occurs with proteins to make up the ribosome which provides the site for translation to occur. Ribosomes can be be located in clusters, or as free individuals, depending upon the final purpose of the altered proteins. Ribosomes are the "factories" that use the message to make essential chemicals for a cell to function.

Chromosomes and Genes are very long thread-like structures in the nucleus of eukaryotic cells, that carry the hereditary information of the cell. They contain a long length of double-stranded DNA coiled up - the famous Double Helix , along with some RNA and special proteins. Bacteria or prokaryotic cells, only have one chromosome each, which is not in the nucleus.

Genes are units or factors of inheritance, each one being a length of DNA containing a particular instruction. For instance your eventual height is determined by a particular gene.

Comparison of relative efficiencies of different types of respiration:

Aerobic respiration:
C 6 H 12 0 6 + 6O 2 > 6H 2 O + 6CO 2 + 2880 kJ
sugar + oxygen > water + carbon dioxide + energy

Anaerobic respiration with ethanol formation (alcohol fermentation):
C 6 H 12 0 6 > 2CH 3 CH 20 H + 2CO 2 + 210 kJ
sugar > ethanol + carbon dioxide + energy

Anaerobic respiration with lactic acid formation (fermentation):
C 6 H 12 0 6 > 2CH 3 CH(OH)COOH + 150 kJ
sugar > lactic acid + energy

For more information use the on-line glossaries for Glycolysis, ATP, Krebs Cycle and Calvin Cycle

Types of association between and among life forms:

Symbiotic - a relationship between two different species of organisms, living together in direct contact.

Mutualistic - a relationship between two symbionts that is of mutual benefit, eg lichen(which is not an individual organism but the symbiosis of cyanobacteria and a fungus).

Commensal - a symbiotic relationship which benefits the symbiont , but has no effect on the host , eg many of the bacteria living inside and on the surface of the human body.

Saprophytic - absorbing nutrients from dead organic matter and decomposing it in the process, eg methanogens - an anaerobic sub-group of archaebacteria, used as decomposers for sewage treatment.

Host - participant which is exploited by the symbiont.
Symbiont - participant living in or on the host.

Microbes have many different ways of metabolizing - getting the energy they need to live, known as nutrition .

Nutrition means the way an organism acquires two resources - energy and carbon - with which it synthesizes organic compounds for it to function, grow, and repair itself. If the species uses light as its energy source it is called a phototroph , if it uses energy from chemicals it is a chemotroph .

Autotrophs are organisms that only require inorganic compounds such as carbon-dioxide for their source of carbon.

Heterotrophs are organisms which require at least one organic nutrient from organisms, or their by-products, as a carbon source for producing their own organic compounds.

Photoautotrophs are photosynthetic bacteria and cyanobacteria which build up carbon-dioxide and water into organic cell materials using energy from sunlight. One product of this process is starch, which is a storage or reserve form of carbon, which can be used when light conditions are too poor to satisfy the immediate needs of the organism. Photosynthetic bacteria have a substance called bacteriochlorophyll, live at the bottom of lakes and pools, and use the hydrogen from hydrogen-sulphide instead of from water, for the chemical process. (The bacteriochlorophyll pigment absorbs light in the extreme UV and infra-red parts of the spectrum which is outside the range used by normal chlorophyll). Purple and green sulfur bacteria use light, carbon-dioxide and hydrogen-sulphide from anaerobic decay, to produce carbohydrate, sulfur and water. Cyanobacteria live in fresh water, seas, soil and lichen, and use a plant-like photosynthesis which releases oxygen as a by-product.
Cyanobacteria Lyngbia © 1997, Microbial Diversity

Photoheterotrophs use light, but obtain their carbon in organic form. Only certain types of prokaryotes can do this. The first life on Earth may have been of this type, using organic material such as amino acids not produced by biological activity.

Chemoautotrophs include many bacteria. They use special chemical processes instead of sunlight to produce organic material from inorganic. Usually compounds other than sugar are oxidized for the chemical process. Colorless sulfur bacteria which live in decaying organic matter where they are unable to use sunlight, oxidize the hydrogen-sulphide given off, to form water and sulfur. Iron bacteria, which live in streams that run over iron-rich rocks, oxidize the iron salts. Hydrogen bacteria can oxidize hydrogen with the formation of water. Nitrifying bacteria are important for enriching soil with nitrogen in a form that can be used by plants. (See nitrification and denitrification).

A saprophytic species of penicillium - mold on orange

Nitrification and de-nitrification: Most of the ammonia from decayed animal and plant proteins in the soil is used by bacteria such as nitrosomonasand nitrococcusas an energy source. This activity oxidizes ammonia to nitrite whereupon other bacteria, nitrobacter, oxidize the nitrite to nitrate in a process called nitrification . Nitrate released from this process can be assimilated by plants through their roots and converted to organic form such as amino acids and proteins. Animals, however, can only assimilate organic nitrogen by eating other animals or plants.

The Food Chain or Food Web: is the process by which biomass is recycled. This involves the movement or cycling of organic chemicals through the environment, ie the movement of carbon, nitrogen, oxygen and water, through plants, animals, fungi, bacteria, etc by respiration and metabolism. For the processes involved, see Cycling Chemicals and Rainforest Ecology

Nanobacteria filaments x35000
© 1999 The Centre for Microscopy and Microanalysis

How small are microbes?

Microbes are extremely small but how small? They are so small that we cannot normally see them. You could fit many thousands on this full stop .

Let us consider a typical bacterium. How big is it and what would it weigh?

It would be something like 0.003 mm long and it would weigh 0.000000000001 grams

Viruses are even smaller and recently nanobacteria a hundred times smaller than common bacteria, have been found. At the other end of the scale, giant bacteria are known. One, Epulopiscium fishelsoni is 0.06 mm long and 0.008 mm wide.

We use microscopes to see individual microorganisms, but it is possible to see colonies with the naked eye. Yeasts and molds are easy to see, as are the matted strands of algae. But in such instances you will be looking at thousands of individuals.

Growing Yeast: Sugar Fermentation

Yeast is most commonly used in the kitchen to make dough rise. Have you ever watched pizza crust or a loaf of bread swell in the oven? Yeast makes the dough expand. But what is yeast exactly and how does it work? Yeast strains are actually made up of living eukaryotic microbes, meaning that they contain cells with nuclei. Being classified as fungi (the same kingdom as mushrooms), yeast is more closely related to you than plants! In this experiment we will be watching yeast come to life as it breaks down sugar, also known as sucrose, through a process called fermentation. Let&rsquos explore how this happens and why!


What is sugar&rsquos effect on yeast?


  • 3 Clear glass cups
  • 2 Teaspoons sugar
  • Water (warm and cold)
  • 3 Small dishes
  • Permanent marker


  1. Fill all three dishes with about 2 inches of cold water
  2. Place your clear glasses in each dish and label them 1, 2, and 3.
  3. In glass 1, mix one teaspoon of yeast, ¼ cup of warm water, and 2 teaspoons of sugar.
  4. In glass 2, mix one teaspoon of yeast with ¼ cup of warm water.
  5. In glass 3, place one teaspoon of yeast in the glass.
  6. Observe each cups reaction. Why do you think the reactions in each glass differed from one another? Try using more of your senses to evaluate your three glasses sight, touch, hearing and smell especially!


The warm water and sugar in glass 1 caused foaming due to fermentation.

Fermentation is a chemical process of breaking down a particular substance by bacteria, microorganisms, or in this case, yeast. The yeast in glass 1 was activated by adding warm water and sugar. The foaming results from the yeast eating the sucrose. Did glass 1 smell different? Typically, the sugar fermentation process gives off heat and/or gas as a waste product. In this experiment glass 1 gave off carbon dioxide as its waste.

Yeast microbes react different in varying environments. Had you tried to mix yeast with sugar and cold water, you would not have had the same results. The environment matters, and if the water were too hot, it would kill the yeast microorganisms. The yeast alone does not react until sugar and warm water are added and mixed to create the fermentation process. To further investigate how carbon dioxide works in this process, you can mix yeast, warm water and sugar in a bottle while attaching a balloon to the open mouth. The balloon will expand as the gas from the yeast fermentation rises.

Disclaimer and Safety Precautions provides the Science Fair Project Ideas for informational purposes only. does not make any guarantee or representation regarding the Science Fair Project Ideas and is not responsible or liable for any loss or damage, directly or indirectly, caused by your use of such information. By accessing the Science Fair Project Ideas, you waive and renounce any claims against that arise thereof. In addition, your access to's website and Science Fair Project Ideas is covered by's Privacy Policy and site Terms of Use, which include limitations on's liability.

Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state's handbook of Science Safety.