A thought on CO2 production with yeast

I see what you mean about yeast needing other things.

When making the beer you bet I added yeast nutrient, NH4 sulfate, some other stuff, and yet some more stuff.

But my brew had about 8 pounds of fermentable sugar, and about 1/4 oz. of those other things.

By far living molecules are made up mosty of carbon, with some (and only some) nitrogen and phosphorous thrown in. DNA has a boatload of N and P, but it is still by weight about 95% carbon.

My pointis that you have a lot of yeast cells, and IF they are growing and dividing, they must be getting that mass from somethwere. That somewhere is the carbon in the sugar.

I may be misunderstanding you, if you disagree with me could you perhaps write a little bit more explaining what you are thinking?
 
1HungryGoldfish said:
In aerobic respiration, we have a situation where the yeast grow and multiply. Take 1 yeast cell, let it grow and divide (and grow a big more), and you have 2 yeast cells of the same size. The extra mass of that second yeast cell must have come from somewhere, and the only source of that mass is the carbon from the sugar. So, we our CO2 estimate from aerobic respiration is very much reduced because so much sugar is being used to create biomass.

If we could force the yeast to eat sugar but NOT actually grow and divide than yes, aerobic respiration would be more efficient in producing CO2. The original poster is quite correct. But we have all forgotton that given oxygen, yeast WILL grow and multiply, and a bunch of that sugar goes into biomass production and not our CO2.
Click to expand...

Regardless if the yeast are working aerobicly or anaerobicly they are constantly reproducing by budding. If you look under a microscope at a yeast culture fermenting sugar, you will see baby yeast cells budding off their parents. You are right that a lot of the carbon ends up going to biomass but what you are not seeing is the need for energy to build that biomass. That energy is produced either by cellular respiration or fermentation. In order to produce a new yeast cell, you need to build a copy of DNA. This takes an enourmous amount of energy which must come from somewhere. This energy comes from the sugar and a byproduct of catabolizing sugar is CO2. This shows that CO2 production will go up in the event of oxygen being present since it now has the ability to build more yeast cells using more glucose as energy producing more CO2. Those babies in turn do the same thing and CO2 production will grow exponentially until the yeast gets killed by an outside source or food runs out.
 
1HungryGoldfish said:
You sure know your stuff, are you a biology major?

Going back to the actual bottle of yeast and sugar, can you explain something to me? When a fresh batch is made up, I never get any CO2 from the bottle to my tank. it is only when the oxygen runs out and fermentation takes place that the pressure buiilds up and I see the bubbles coming out from my tube (the end in the tank).

But if I understnad you correctly there should be plentyof CO2 being made during aerobic respiration. Then why isn't my tubing bubbling? How come it only bubbles during fermentation, without oxygen.

?????

It would be great for us (cheap) CO2 adders if this biochemistry would work out.
Click to expand...

Next time you mix up a batch, look closely at the mix, it should start to bubble slowly as the yeast activates (pretty much wakes up). The reason it takes time is because the CO2 has to build up pressure to push the water out of the way. Then it starts to bubble but remember that 70% of air is Nitrogen. This nitrogen will still be in the soda bottle and has to be pushed out before you get CO2 saturation and the bubbles dissolving effect you see. You also have to remember that the yeast even though it is producing CO2 in the beginning, it is still stored in a water solution and that water has to become saturated with CO2 before the CO2 will start to bubble out in greater numbers. CO2 production also will increase over time until the alchohol or lack of food starts to affect it because the yeast will be reproducing increasing CO2 production as numbers increase.
 
The yeast may be reproducing more, but the aerobic respiration of yeast still produces more CO2 for the following reasons and others:
1. Through aerobic respiration ethanol is not produced (unlike anaerobic respiration) which uses alot of carbon to produce. The only by-products of aerobic respiration are H2O and CO2.
2.If you are only using sugar, water, and yeast in your solution like most people, then there is a limit on how much the yeast can reproduce without its other required nutrients anyways negating the whole argument about increased reproduction using up too much carbon.
 
Last edited:
1HungryGoldfishM, Just because they are made up of 95% carbon does not mean that they can make all of those carbon structures from sugar alone. I will try to find some examples.
 
McJosh13 said:
1HungryGoldfishM, Just because they are made up of 95% carbon does not mean that they can make all of those carbon structures from sugar alone. I will try to find some examples.
Click to expand...

That is correct. Some amino acids contain sulfur and then you need certain ions such as Calcium to turn on and off some enzymes...

The average yeast reactor will extract these minerals from the water they are growing in. We are not talking about large scale yeast production where this would need to be supplemented. In the average yeast reactor, the ethanol will kill the yeast before the minerals get used up.
 
You must log in or register to reply here.
AquariaCentral.com
Top Bottom