Fermentation quesdtion

[cjg444]

I swear I've looked for this but still perplexed. Needless to say, I'm very green. Now, I've read a number of places that 70% of the alcohol is made in the first 3-5 days.
So... first there's the aerobic fermentation, (also called primary?) where we mix it up to get the O2 in so the yeast can reproduce, taking 3-5 days. Check. Then, after using up the O2, they go into anaerobic (secondary?) whereas one of the byproducts is alcohol. Check.
But how can it produce most of the alcohol in the first 3-5 days if it must be deprived of O2 to produce alcohol, and we're busy splashing it around adding O2? And why after 3-5 days do we suddenly stop adding O2 and rack to secondary?
Any replies are greatly appreciated. (Especially using small words. And pictures.)

 

[pumpkinman2012]

cjg444,
These are very good questions, one of the reasons that you will see a lot of post that refer to proper rehydration of yeast using proper temps and hydration nutrients such as Go-Ferm to ensure that a health yeast population is growing, this includes avoid leaving the yeast hydrated for more than 30 mins, after this time the yeast will start to die off without adding a food source such as must (it will be high in natural sugars), selecting the proper yeast strain that can accommodate the sugar level (brix) of the must, maintaining proper fermentation temps, and using yeast nutrients to avoid stressed yeast.
We do all of this to because a good fermentation requires a large population of strong healthy yeast cells that can finish fermenting before the resources are all used up (this is where yeast nutrients come into play), rising alcohol levels, and old age will make them go dormant, not to mention that reproduction of the yeast cells is much slower when the oxygen is depleted.

A few points:
I wouldn't stir up the must to introduce oxygen, unlike beer, wine will get oxidized.
I highly recommend to rack the wine only when it has fermented to dry, by racking early, you can end up with a slow or stuck fermentation, and again, you want to avoid introducing oxygen to the wine.
Yeast doesn't know days (as in the 3-5 days), the only way that you can be sure of a completed fermentation is with a hydrometer.
I hope that this helps.

 

[bernardsmith]

Not a chemist but I believe that yeast is incredibly adaptive and it can reproduce and maintain itself both with and without oxygen, however, with oxygen it focuses on budding, (repairing and reproducing- still using the sugars and nutrients in the must, and on modifying its cellular structure to transport the sugars through the cell walls. Without oxygen it will be less able to develop the yeast colony but those that are viable will tend to ferment the sugars. I am not sure that yeast in your fermenter all go into an anaerobic state at the same time or that after a week or even a month that the surviving viable yeast or newly budded yeast don't need O2. The issue - as I understand it is whether the wine maker wants the yeast to gain access to O2 or not. And I think the typical answer is that appropriate amounts of O2 during the early days of fermentation are not bad for the wine and are great for the yeast. After much of the fermentation has occurred then the O2 is bad for the wine (oxidation) but still good for the yeast and that cost/benefit balance suggests that you want to provide O2 early and restrict it later...

 

[cjg444]

Thanks guys - this helps a lot. I can follow the directions of a recipe, but I like to know why everything does what it does, and some of the definitions seem contradictory.
So it can make alcohol without O2 deprivation, but prefers to multiply under those conditions, and then we (for lack of a better term) force the fermentation through a lack of O2, correct?

 

[fuelish]

cjg444,

I wouldn't stir up the must to introduce oxygen, unlike beer, wine will get oxidized.

Beer oxidizes as well....It seems a lot of beer brewers are more anal about that than the meaders, and their product (other than special "big" beers meant to age) doesn't really sit around long, in the scheme of things compared to mead or wine....I don't worry about it either way....maybe I like the taste of oxidized fertmented beverages and just don't realize it....LOL

 

[sunlandwines]

Ok, so I have a batch of lemon wine that's been happily bubbling away since Sunday morning (I pitched the yeast Saturday). Currently I've got the lid resting (the lid has a bung hole) on top with a clean towel draped over. Is there ever a time where I'm going to want to put an airlock on it, or do I wait until I rack to the secondary?

 

[bernardsmith]

IMO, when you rack to the secondary you rack because almost all the sugar has been fermented and so the wine is no longer producing enough CO2 to keep a blanket of that gas between the air and and the wine. So the use of an airlock makes sense at that point and that point is - IMO - at a gravity of about 1.005

 

[sunlandwines]

I started with SG at 1.090. When should I first check it, do you think?

 

[pumpkinman2012]

I agree with Bernardsmith, I don't rack before my wine is fermented to dry.
I usually ferment my smaller batches in a plastic brewcraft fermenting bucket with the lid and the port for the air lock, I've always left enough room for oxygen and put the airlock on right from the beginning.
For my larger batches, I use a 32 gal or 42 or 44 gal brute and put the lid on it to keep the pesky fruit flies out of my wine.
I wouldn't rack off the yeast before it has fermented to dry, you run the risk of a very slow or stuck fermentation.

Sunlandwines, not to be a wise guy, but yeast don't know days, I'd wait until you hear the airlock slow down to almost no activity before checking, and still and that point, you can gently stir the yeast back into suspension to try to get a fer more days of fermentation out of it. I'd get Fermaid K yeast nutrient to make sure that your yeast remains healthy and happy and ferments to dry.

 

[sunlandwines]

I agree with Bernardsmith, I don't rack before my wine is fermented to dry.
I usually ferment my smaller batches in a plastic brewcraft fermenting bucket with the lid and the port for the air lock, I've always left enough room for oxygen and put the airlock on right from the beginning.
For my larger batches, I use a 32 gal or 42 or 44 gal brute and put the lid on it to keep the pesky fruit flies out of my wine.
I wouldn't rack off the yeast before it has fermented to dry, you run the risk of a very slow or stuck fermentation.

Sunlandwines, not to be a wise guy, but yeast don't know days, I'd wait until you hear the airlock slow down to almost no activity before checking, and still and that point, you can gently stir the yeast back into suspension to try to get a fer more days of fermentation out of it. I'd get Fermaid K yeast nutrient to make sure that your yeast remains healthy and happy and ferments to dry.

Thanks, Pumpkinman. I added yeast nutrient prior when I added campden and pectin enzyme. Should I throw some more in when I stir?

 

[pumpkinman2012]

The recommended yeast nutrient "schedule" is to take the amount of nutrient called for, let's say 1 gram per gallon and split it up over 2-3 applications; the first being at the start of fermentation, and again at 1/3 sugar depletion.
One of the reasons that I would avoid adding yeast nutrients before fermentation begins is that the yeast which are still developing can be shocked by the nitrogen, of course you can avoid this by using Fermaid O which has an organic form of nitrogen at the same time as you pitch your yeast.