Yeast Life Span and Nutrient Needs

[BarrelMonkey]

Actually yeast have 10 (ten!) enzymes that break down sucrose.

yes - but it also happens spontaneously in acidic conditions, faster at higher temperature. When I'm making sparkling wine (grape or elderflower), I want to make life as easy on the yeast as possible. So I prepare (table) sugar by heating it in the presence of weak acid (tartaric or lemon juice, depending on the wine...) this substantially converts sucrose to fructose and glucose. (It's called inverting the sugar due to the change in optical properties... sucrose rotates polarized light in one direction, whereas glucose and fructose rotate it in the other. And one of the most important classes of enzyme that do this are the invertases.)

 

[BigDaveK]

yes - but it also happens spontaneously in acidic conditions, faster at higher temperature. When I'm making sparkling wine (grape or elderflower), I want to make life as easy on the yeast as possible. So I prepare (table) sugar by heating it in the presence of weak acid (tartaric or lemon juice, depending on the wine...) this substantially converts sucrose to fructose and glucose. (It's called inverting the sugar due to the change in optical properties... sucrose rotates polarized light in one direction, whereas glucose and fructose rotate it in the other. And one of the most important classes of enzyme that do this are the invertases.)

Some members use invert sugar. I've never used it for wine making but believe it or not I've made it to use with my baking. I never wanted to pay the prices for invert sugar marketed for bakers. I'm cheap.

 

[Rice_Guy]

From a lab point of view we measure reducing sugars via wet chemistry which contains sucrose/ fructose/ glucose/ and a few others as birch sugar (xylose)/ milk sugar (lactose). To run individual sugars would use HPLC which gets expensive, not practical.
Yeast stop reproducing when the system gets to 9% alcohol. Step feeding will not make them restart that type of metabolism/ demand for YAN. Threads like this make me a stronger proponent of organic nitrogen and lots of YAN in the first third of fermentation! ,, (humm where did the post 5-6 weeks back with YAN vs fruit crops go? That is part of the metabolism story.)

Excellent articles @David Violante .

 

[David Violante]

So, am I right in assuming the graph would be slightly different for different yeasts?
Another thought, does step feeding extend the stationary phase?

I completely misinterpreted the second part of the question… I was thinking of step additions of sugar to increase final ABV. I believe that would increase the time of the stationary phase. No new yeast, but it would take longer to get through the phase if you keep adding sugar.

I continue to step feed nutrients to yeast in the first phase, and use GoFerm for better nutrition in rehydration.

 

[dianemaycotte]

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.

The information and article that you posted are fascinating! Thanks!