When to cover

[Maheesh]

Fermenting to dry in stainless tank, when should I put my lid on, in terms of remaining brix? Thx.

 

[Rice_Guy]

Today I was exploring a question that has been on my mind, and I found this: https://www.researchgate.net/figure...ion-changes-in-key-metabolites_fig1_332733632 (scroll down and click on "Download full text" to get the entire article.

There is a lot of information here that is not of immediate interest to me. But I found section 4 "Chronological Life Span in Wine Yeasts" quite interesting. It included this chart:
View attachment 95875
In the accompanying text I found this comment:

From this I learned that the main need for nitrogen is during the exponential growth phase. But most of the alcohol production takes place during the stationary phase, when the yeast is no longer reproducing. That is why the SNA used by mead makers stops adding nutrients at the 1/3 sugar break, when 1/3 of the sugar has been digested by the yeast. The goal is to have a healthy yeast population by the end of the exponential growth phase, so that the existing yeast can finish the process of fermentation. I have not yet found a clear statement on what nutrients the yeast need once they reach the stationary phase.

The green and red text is explained here:

In other words, the items in green text help the yeast to stay alive and keep working, and the ones in red help with aging.

I thought you would find this interesting, so I thought I'd share it here.

Whites, 1/3 sugar is where the yeast population maxes and they switch to anaerobic.
Reds, it depends. Again oxygen isn’t needed after 1/3 sugar. The mixing of skins to prevent mold growth means you have your tank open. In this case after pressing.
All in all oxygen is the enemy of alcohol producing acetaldehyde. Unless I could do a novel system as fermentation in a bag sooner rather than extending past zero sugar.