How does Yeast Actually do it's voodoo?

[lazarwolf]

So we all talk about yeast a lot. We all say Mr. Malty says pitch this much, or woodland says viability is paramount... We all say the flavor profile of this yeast is spicy, or phenolic, or sulphury...

But I want to know... how does yeast actually do what it does...

to that end I have purchased "yeast" and "principles of brewing science"

But Id love to see some conversations about the actual chemistry of yeast.

1. It doesn't have a mouth, so how does it absorb and eat sugar?
What chemicals are involved? how do these change at different temperatures?
2. What chemicals are released in the conversion of sugar to alcohol...

 

[bruteforce]

You might check into a book on basic biology. (Note I'm not trying to be a dick, just that I learned a lot of this stuff in college bio)

More or less yeast absorbs sugar through the cell wall like any other single cell organism. There are certain enzymes that allow it to break apart larger sugar molecules and burn them as energy. C02 and various alcohols are the by-products. Temperature changes things because reactions happen faster at higher temp (providing it isn't high enough to kill the organism)

So thats the quickest and most basic (to the point of missing some good stuff) explanation I can give, but those books should have some good stuff for you. Good luck!

 

[ChefRex]

You drink its poop, need I say more

 

[AnthonyUK]

Last year I signed up for an online course on brewing science which covered this topic in detail.
As interesting as it may be, I don't feel it helped one bit as far as brewing beer is concerned.

 

[edues]

Its great when your brew comes to life! It starts moving around, it breaths, and even makes its own heat. All the nuturing you put into it to make it good its like raising a child,without dipers, teenage drama and the possible child support. I like making it as much as drinking it. Maybe even more. Its like playing god. After all he did turn water into wine. Hahaha.

 

[lazarwolf]

I know what yeast does, and I am blessed to have an excellent education which included basic biology, and an advanced degree (although not in biology). My question is more specific. How does yeast absorb sugar? is the process physical or chemical? if it is chemical what chemicals are released? in what quantities? what factors influence this other than temperature?
What chemicals are responsible for the major metabolic pathway?

 

[DurtyChemist]

I know what yeast does, and I am blessed to have an excellent education which included basic biology, and an advanced degree (although not in biology). My question is more specific. How does yeast absorb sugar? is the process physical or chemical? if it is chemical what chemicals are released? in what quantities? what factors influence this other than temperature?
What chemicals are responsible for the major metabolic pathway?

Seriously a quality biology book will cover this. Microbiology might also. I don't think I have anymore but stuff that comes to mind is Krebs Cycle, private dehydrogenase, glycosylation, NAD, NADH, ADP, ATP, mitochondria, and that's it currently. I think I remember my Biochemistry 400 course having the best detail as far as alcohol production and alcohol dehydrogenase just popped into my brain.

Yeast absorb sugar through pores in their membrane. It's physical. Factors that influence it are obviously sugar availability and proximity, temperature, pH, if the cell is actively reproducing or in a latent stage or infected with a virus.

 

[ArcLight]

I know what yeast does, and I am blessed to have an excellent education which included basic biology, and an advanced degree (although not in biology). My question is more specific. How does yeast absorb sugar? is the process physical or chemical? if it is chemical what chemicals are released? in what quantities? what factors influence this other than temperature?
What chemicals are responsible for the major metabolic pathway?

A good book on molecular biology will tell you what you want to know.
You can get a prior edition for less:
http://www.amazon.com/dp/0815344546/?tag=skimlinks_replacement-20

http://www.amazon.com/dp/0815344325/?tag=skimlinks_replacement-20

>> How does yeast absorb sugar?


Cells can transport molecules across their membrane/wall via passive or active transport. There may be holes called channels, or there may be protein structures that bond with a molecule, change shape, and allow the molecule to enter the cell.

>. is the process physical or chemical?

It's both. It's physical, but it's chemical also because there is molecular bonding involved. In the case of active transport, ATP (energy) is consumed changing the shape of the transporter protein.


>>What chemicals are responsible for the major metabolic pathway?

If you want to know the enzymes used in Glycolysis, then the 2nd book I listed above will tell you. Here is an "overview"
https://en.wikipedia.org/wiki/Substrate-level_phosphorylation

You may also be interested in the Crabtree effect and what supresses yeasts cellular respiration in the presence of glucose above a low thresh hold (0.3 - 0.5%)

 

[ColoHox]

 

[lazarwolf]

You guys are great. I just bought those books. It seems to me that the very best brewers I have ever met, really understand Yeast above all other brewing issues.

Next Question.

Why does yeast need oxygen, and nitrogen to grow and multiply?

 

[ArcLight]

>>Next Question.

>>Why does yeast need oxygen, and nitrogen to grow and multiply?

Brewers Yeast (such as Saccharomyces cerevisiae) is a facultative anaerobe, meaning it doesn't need Oxygen for respiration (producing energy) because it can produce energy via fermentation. S Cerevisiae can use Oxygen and respire (producing much more ATP) provided the sugar level is very low (less than 0.5%).

Oxygen is needed for other things, such as building up cell walls, and other organelles in the cell.
Oxygen is present in Carbonyl and Carboxyl groups that are used in many organic molecules.

Nitrogen is a component of proteins (ex: enzymes and structural components) and and other molecules and used in a wide range of processes and organelles.

ATP contains Oxygen and Nitrogen for example. Without ATP, no energy and no yeast.

The books I listed above will answer this question in far more detail.

Yeast can consume dead yeast to obtain some elements like Nitrogen, but it's faster if they can get it from their food. That's why you add yeast nutrient to nutrient deficient food like apple juice (for cider) or honey (for Mead).

 

[DurtyChemist]

Yeast also need Carbon. No one ever talks about Carbon but it's required for yeast. Look at a glucose molecule.

 

[trentm]

You guys are great. I just bought those books. It seems to me that the very best brewers I have ever met, really understand Yeast above all other brewing issues.
Next Question.
Why does yeast need oxygen, and nitrogen to grow and multiply?

For brewing concerns perhaps the most important role of O2 is its role in the synthesis of lipids. Lipids are metabolized by the yeast cell from squalene but without O2 this metabolite (lipids) cannot be formed. Lipids make the cell wall elastic and fluid which not only helps with reproduction but also intake of sugars and output of alcohols near the end of fermentation. Once the fermentation is anaerobic, lipids cannot be formed and with each new bud the lipids from the mother cell are shared equally with the new daughter cell. With plenty of O2 a yeast cell can contain up to 5% lipids. But in an anaerobic environment where lipid formation has ceased, after the first doubling the new yeast cell now contains 2.5% lipids and after the next split the cell contains 1.25% and then 0.63%. It is at this point that the cell wall loses its elasticity and becomes leathery, the cell may not be able to bud and is more challenged to uptake sugar and remove alcohol. The buildup of alcohol within the cell can become toxic and deadly. The lack of sufficient O2 at the beginning of fermentation may be the greatest factor in under attenuated beer and stuck fermentations.

 

[lazarwolf]

Fantastic information.