Yeast Lifecycle Factors

[Raptor99]

In an earlier post, I raised the issue of how the yeast "knows" to switch from the exponential growth phase to the stationary phase. How does the yeast know when to stop reproducing? I can't find that tread right now, so I will start a new one here in the Wine Making Science forum where it belongs. I spent some further time studying this article: https://www.researchgate.net/public...ife_Span_and_its_Impact_on_Food_Fermentations. I will share what I have learned so far.

The article confirms that most of the ethanol is produced during the stationary phase:

The bulk of sugar fermentation takes place after cells enter the nondividing state due to nitrogen limitation and/or ethanol accumulation.

It also notes that the cells enter the nondividing (stationary) phase due to "nitrogen limitation and/or ethanol accumulation." That means that especially for hard cider or a low alcohol wine, it is important to get the nitrogen level right so that is is neither too high nor too low. We want the cells to stop dividing at a certain point, which is dependent on the amount of sugar in the wine.

The article describes two types of yeast life spans, which are replicative live span (RLS) and chronological life span (CLS). The RLS is due to the fact that the yeast cells can reproduce a limited number of times before they will stop dividing. The CLS describes the fact that individual yeast cells will live a certain amount of time, depending on conditions, before they die. There are some implications related to stuck fermentations. How do you prevent the cells from dying before all of the sugar is digested?

The only intervention that has proven useful to extend life span from yeast (both the RLS and CLS) to primates to date is dietary restriction (DR); i.e., reducing a particular or the total nutrient intake without causing malnutrition [1,18]. When the number of calories is lowered, this intervention is referred to as calorie restriction.

If we are facing a situation in which the yeast cells are dying during the stationary phase before the sugar is gone, the problem might be too much nitrogen, which reduces the chronological life span (CLS) of the cells. High alcohol wines are more likely to have this problem, because the increasing ethanol level is harmful to the yeast.

My takeaway is that I will try to calculate the correct amount of nutrients for each batch of wine. Either too little or too much can lead to problems. For a detailed explanation of YAN see this article: Advanced Nutrients in Meadmaking and the spreadsheet created by the author: You must create a copy of the spreadsheet to edit it. This is what I use in making mead, and I have started to use it for wine and cider as well.

 

[BigDaveK]

I'm there with you, doing a lot of reading. Yeast are incredibly interesting and complex and it seems everything plays a part and nitrogen is just one piece. Oxygen is extremely important at the beginning for the increase of yeast biomass and stronger cell walls to deal with higher ethanol. And I don't remember the article mentioning the Crabtree Effect where the yeast will start producing ethanol very early to poison the environment for competing microbes. And pH is important. And temp is important. And yeast strain is important. And yes nitrogen and carbon is important.
I'm not disputing what you're saying, just that there's a whole lot going on.
Incredibly interesting creatures.

 

[Raptor99]

@BigDaveK Yep, it's complicated. I appreciate the research papers that you have shared on the forum.

The specific question that I was wondering about is what causes the yeast to stop reproducing and shift from exponential growth to the stationary phase. That seem important from a wine making perspective. We want to see the shift at the right time, neither too early nor too late. While I'm sure that there are other factors, the one mentioned in this study is having the optimal nutrient level.

As I quoted above,

The only intervention that has proven useful to extend life span from yeast (both the RLS and CLS) to primates to date is dietary restriction (DR); i.e., reducing a particular or the total nutrient intake without causing malnutrition [1,18]. When the number of calories is lowered, this intervention is referred to as calorie restriction.

It does not list the other factors they studied, but their conclusion starts with "The only intervention..." So I want to pay attention to that.

 

[BigDaveK]

The problem with scientific papers is that there are so many variables to wine making and generally each paper concentrates on one or two variables. That's not a bad thing, we just need to read more. I don't think we'll have all the answers any time soon but with luck we'll have fewer questions.
Here's a couple more for you. Don't know if I posted these. I saved so many. Good thing I enjoy this because I'll be reading for a while to come.

https://pubmed.ncbi.nlm.nih.gov/18215224/
https://pubmed.ncbi.nlm.nih.gov/32309422/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC134739/

 

[winemanden]

The problem with scientific papers is that there are so many variables to wine making and generally each paper concentrates on one or two variables.

Another problem is that work done for scientific papers is done under controlled laboratory conditions. Most home winemakers don't have facilities like that!

 

[Raptor99]

Another problem is that work done for scientific papers is done under controlled laboratory conditions. Most home winemakers don't have facilities like that!

True, but controlled laboratory studies are helpful to understand the underlying mechanism. The exact numbers might be different in real world conditions, but the effects of low vs high nutrient levels is probably similar.

 

[Rice_Guy]

Another problem is that work done for scientific papers is done under controlled laboratory conditions. Most home winemakers don't have facilities like that!

Well, you don’t need to have a lab setup to use journal research. A good paper will point a direction. The method of papers is to reduce the variation and ask if I change one thing X, what happens? This has been extremely useful in the factory since it gives a predictive model of the world. With a model I can go to a programmable controller and say if one sensor reading changes I should respond by changing one effect Y. , ,,, . (besides industry probably is funding/ providing free ingredient and in my case reviewing papers to judge if they ring true)

The worst case of poor modeling I have seen was a customer building a new product using one fifty pound bag of rice flour. One might think that is extremely clean,, but oxidation over a year of testing meant that they were trying to control with one control parameter when they should have had at least two.

If honest I would have to say patent 4,649,055 comes from reading the journals and just applying pHd modeling in a factory.

 

[sour_grapes]

If honest I would have to say patent 4,649,055 comes from reading the journals and just applying pHd modeling in a factory.

Perhaps TOO modest!

 

[Rice_Guy]

An example of using the journals/ ,,, and not all articles are created equally useful for wine at home. The fungicides Boscalid and Difenoconazole change metabolic pathways so that strawberries aren’t as flavorful, ,,,, I guess in my home garden I will not use fungicides and make a gallon of wine, and then compare flavor with wine made from grocery store strawberries.
https://pubs.acs.org/doi/abs/10.1021/acs.jafc.2c08157#
Next for laughs, I could try organically grown Marquette against vines treated with Mancozeb or Ralley or Benolate or Captan. . . . etc