Beer Fermentation Tanks: Difference between revisions

From MicrobeWiki, the student-edited microbiology resource
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=References=
=References=
[Sample reference] [http://ijs.sgmjournals.org/cgi/reprint/50/2/489 Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "''Palaeococcus ferrophilus'' gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". ''International Journal of Systematic and Evolutionary Microbiology''. 2000. Volume 50. p. 489-500.]


1.  [http://en.wikipedia.org/wiki/Lager_yeast “Saccharomyces pastorianus”. ''Wikipedia''. 7 August 2008.]
1.  [http://en.wikipedia.org/wiki/Lager_yeast “Saccharomyces pastorianus”. ''Wikipedia''. 7 August 2008.]
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13.  [http://www.ncbi.nlm.nih.gov/pubmed/18193418 Omura, F. "Targeting of mitochondrial Saccharomyces cerevisiae Ilv5p to the cytosol and its effect on vicinal diketone formation in brewing.". ''Applied Microbiology and Biotechnology''. March 2008. Pages 503-513.]




Edited by Daniel Stromwall, Andrea Lin, and Chrissta Maracle; students of [mailto:ralarsen@ucsd.edu Rachel Larsen]
Edited by Daniel Stromwall, Andrea Lin, and Chrissta Maracle; students of [mailto:ralarsen@ucsd.edu Rachel Larsen]

Revision as of 08:54, 28 August 2008

Description of Niche

Where located?

Physical Conditions?

What are the conditions in your niche? Temperature, pressure, pH, moisture, etc.

Influence by Adjacent Communities (if any)

Is your niche close to another niche or influenced by another community of organisms?

Conditions under which the environment changes

Do any of the physical conditions change? Are there chemicals, other organisms, nutrients, etc. that might change the community of your niche.

Who lives there?

Ale Fermenting Yeast

Which microbes are present?

When brewing ales, ideally the only microbe found in the fermentation vat is Saccharomyces cerevisiae. This yeast is often referred to as“top fermenting” yeast because during the fermentation process the yeast associate with the rising CO2 bubbles creating a thick foamy layer at the top of the fermentation vat. This type of yeast is usually fermented at warmer temperatures ranging from 10-25°C (50-77°F) which decreases the fermentation time and creates a type of beer that is usually fruitier in flavor (7).

Are there any other non-microbes present?

Contamination of the wort is possible if it is uninoculated. This can lead to the presence of various other organisms such as bacteria including Pediococcus, spp. and Lactobacillus, spp., as well as other wild type yeasts such as Hansenula, Dekkera, Brettanomyces, Candida, and Pichia. To guard against contamination a yeast inoculum is added which changes the conditions in the fermentation vat so as to create an environment that is more favorable to the desired type of yeast. This is characterized by a drop in pH, the decrease in oxygen with a rise in carbon dioxide and ethanol, as well as the hops having an antimicrobial trait (8).

Do the microbes that are present interact with each other?

After the yeast inoculum is added to the wort, the environment of the fermentation vat should have conditions that are suitable only for a specific strain of yeast, so there would not be other microbes for Saccharomyces cerevisiae to interact with. However, as the nutrient sources in the fermentation vat begin to run out, S. cerevisiae will interact with itself in a process known as flocculation. In the S. cerevisiae species flocculation is a reversible asexual process that causes the yeast to stick to each other and form clumps known as flocs. Flocculation is carried out through the interactions between Ca+ dependent proteins and sugars as well as interactions between lectin like surface proteins, known as flocculins, and the cell wall mannan of surrounding cells (9). Flocculation begins to occur after fermentation is completed and the yeast are in stationary phase. These flocs then associate with the carbon dioxide bubbles and travel to the top of the vat where they form a thick layer(10). This is very helpful to brewers because they can easily separate the yeast from the beer and can even reuse the yeast again in a different batch.

Do the microbes change their environment?

Do they alter pH, attach to surfaces, secrete anything, etc. etc.

Do the microbes carry out any metabolism that affects their environment?

Saccharomyces cerevisiae affects their environment through two forms of respiration both aerobic and anaerobic. The beginning environment is a solution known as wort which consists of a liquid extracted from a mixture of water, mashed barley, and hops(11). This liquid contains the sugars, nitrogen (mostly in the form of amino acids), and vitamins that the yeast will use to survive. The yeast is then added to the wort and after it completes the lag phase of its life cycle, begins aerobic fermentation using oxygen in the environment to oxidize acids, which then causes a drop in pH and also forms carbon dioxide. Once the environment is completely stripped of oxygen, the yeast begins anaerobic respiration, otherwise known as fermentation. This process changes fermentable sugars into ethanol, but other byproducts such as esters, ketones, and sulfur compounds are created as well, all of which affect the flavor of the beer. Ales will contain a higher content of these flavor compounds contributing to its fruitier flavors (12).

Lager Fermenting Yeast

Which microbes are present?

Ideally during the fermentation step in beer brewing, the only microbe present is the specific strain of yeast that the brewer uses. The most common yeast used for brewing lager is Saccharomyces pastorianus (also called Saccharomyces carlsbergensis) (1). These are cold, bottom fermenting yeast (as opposed to the top fermenting yeast for ales). They ferment in a temperature range of 7-15°C (45-59°F) (2). Because of the lower range they ferment at a slower rate, resulting in less foam and thus when the yeast flocculates, it settles to the bottom of the tank.

Are there any other non-microbes present?

There are no non-microbes living in a beer fermentation vat (preferably).

Do the microbes that are present interact with each other?

S. pastorianus naturally ferments for a longer time than ale yeasts which calls for the necessity of careful sanitization of the vat and area as to avoid contamination by wild microbes. Due to the presence of only a single population of yeast, microbe interaction is limited to how the yeast within the population grow. One very important trait of yeast for brewers is that at certain conditions, yeast flocculates. The conditions are ideally when the sugars within the wort have been converted to ethanol and available energy sources are low. Flocculation is the aggregation of yeast cells into clumps that sediment in the environment. With S. pastorianus, these clumps sink to the bottom of the tank, hence the name bottom-fermenting yeast. In brewing yeast, this is an asexual aggregation where the yeast prepares for dormancy by producing glycogen: the microbe’s preparation at the end of the stationary phase caused by starvation. In S. pastorianus, flocculation is controlled by a lectin-mediated mechanism and requires Ca+. Lectin is recognized by mannan receptors on yeast cells, and so the presence of mannose blocks this mechanism. Unlike with ale yeasts, flocculation of S. pastorianus, is not affected by the pH of the environment. (3)

Do the microbes change their environment?

From a human standpoint, the whole point of using yeast for beer fermentation is to transform the sugars within the wort into ethanol and other flavor changing molecules. The preparation of the environment is as follows: the wort is prepared by boiling and quick chilling used to help coagulate excess protein for removal. Also by dropping the temperature to optimum growth range, premature fermentation is prevented. Once out of the lag phase, the yeast reaches the growth phase where it uses aerobic respiration until all the oxygen is removed from the environment. While in respiration phase, the yeast oxidizes acid compounds, dropping pH of the environment. The oxygen is used up during respiration and the carbon dioxide produced by the yeast also helps to remove any traces of oxygen, called “scrubbing”. Now the yeast switches to anaerobic respiration: fermentation. During fermentation the simple sugars are converted to ethanol and carbon dioxide. In lagers however, unlike ales, the presence of esters (fruity flavors) and diacetyl (butterscotch-like flavors) is considered a flaw. Due to the low temperatures at which S. pastorianus ferments, a naturally lower amount of esters and diacetyl is produced. The low temperature is also the cause for the production of sulfur compounds which is gradually incorporated and gives the lager the clean, crisp taste. Once completed, the wort will have lowered simple sugar content, elevated ethanol content, carbon dioxide, sulfer compounds, and lowered pH and specific gravity. (4)

Do the microbes carry out any metabolism that affects their environment?

The metabolism of S. pastorianus is responsible for the multitudes of changes in its environment which people love. However, the environment is also manipulated by people in several ways to cause S. pastorianus to metabolize certain compounds with the goal of manipulating the final environment’s characteristics. Obviously during fermentation sugars are metabolized into ethanol and carbon dioxide. However, one of the most important difference between lager yeast and ale yeast is the environment’s content of diacetyl. Diacetyl is a by-product of valine synthesis where the yeast produces α-acetolactate. Once α-acetolactate leaves the cell, it becomes decarboxylated into diacetyl by the environment. Lager fermentation is broken into two steps: the initial fermentation and the much longer and colder second step referred to as lagering. Towards the end of the first fermentation step, the temperature of the environment is raised to about 50-55°F for 2-5 days called diacetyl rest. This invigorates the yeast and causes it to absorb and metabolize the diacetyl, reducing the ketone groups to acetion and 2,3-butanediol which are largely flavorless. (5) After this step the liquid environment is transferred to a secondary vat which removes protein trub and excess yeast which has already flocculated. In the secondary fermentation, the temperature is dropped to 33-35°F and lasts for 8-12 weeks. During this the yeast will all flocculate and sink allowing for the easy removal and collection of the yeast for later use. (6)

Current Research

Enter summaries of the most recent research. You may find it more appropriate to include this as a subsection under several of your other sections rather than separately here at the end. You should include at least FOUR topics of research and summarize each in terms of the question being asked, the results so far, and the topics for future study. (more will be expected from larger groups than from smaller groups)

References

1. “Saccharomyces pastorianus”. Wikipedia. 7 August 2008.

2. Goldammer, Ted. “The Brewers’ Handbook, The Complete Book to Brewing Beer”. December 2000. Chapter 4: Lager.

3. Dengis, Pascale B., L. R. Nélissen, and Paul G. Rouxhet. “Mechanisms of Yeast Flocculation: Comparison of Top- and Bottom-Fermenting Strains”. Applied and Environmental Microbiology. February 1995. Pages 718-728.

4. Oliver, John. “10 Keys to Great Lager”. Brew your own: The How-to Homebrew beer magazine. September 1999.

5. “Diacetyl”. Wikipedia. 16 August 2008.

6. “Laagering FAQs”. Midwest: Homebrewing & Winemaking Supplies. 2005

7. Goldammer, Ted. “The Brewers’ Handbook, The Complete Book to Brewing Beer”. December 2000. Chapter 4. 8 9 10

13. Omura, F. "Targeting of mitochondrial Saccharomyces cerevisiae Ilv5p to the cytosol and its effect on vicinal diketone formation in brewing.". Applied Microbiology and Biotechnology. March 2008. Pages 503-513.


Edited by Daniel Stromwall, Andrea Lin, and Chrissta Maracle; students of Rachel Larsen