Yeast Life Span and Nutrient Needs

[Raptor99]

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:

In the accompanying text I found this comment:

The bulk of sugar fermentation takes place after cells enter the nondividing state due to nitrogen limitation and/or ethanol accumulation. The viability and vitality of yeast in the stationary phase are relevant factors to help achieve full fermentation.

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:

Positive regulators of the chronological life span are indicated in green and pro-aging factors are indicated in red.

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.

 

[Raptor99]

I just found a good overview in this article: How Does Wine Fermentation Work? — Bruliam Wines Yeast need oxygen, protein, and nitrogen before the ethanol levels get too high so that they can build up their "armor" to withstand higher ethanol levels. In other words, during the growth phase the yeast need to prepare themselves for the stationary phase.

The chart at the beginning of the article also shows the brix level vs. time. During the growth phase, the sugar levels don't change very much. Then once the stationary phase is reached, the majority of the sugar is digested within two days!

My takeaway from this is that slow or stuck fermentations might be caused by an unhealthy yeast population which is unable to cope as the ethanol levels rise. An ounce of prevention is worth more than a pound of cure, so I want to do everything I can to ensure a healthy yeast population in the early part of fermentation. Take good care of your yeast, and they will do the rest.

 

[nodor]

Thats scary. It seemed like I understood what was being said even though I didn't know half the words lol

 

[Rice_Guy]

I think you mean TONSA as in Total Organic Nitrogen staged addition

. . . .. 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,

, , oxygen is also a nutrient, sterols and vitamins are required nutrients.

An excellent post! ,,,, Have you looked into the Scott Lab Handbook about nutrition?

 

[winemaker81]

This explains why the overnight starters produce such a quick ferment, as a large portion of the exponential growth takes place in the more ideal environment of the starter. I was certain this was true, but this article confirms it.

 

[Raptor99]

I think you mean TONSA as in Total Organic Nitrogen staged addition

TOSNA is one protocol for SNA, but there are others: Nutrients in Mead Making - Mead University — You To Brew

Have you looked into the Scott Lab Handbook about nutrition?

I looked at that a while back, but not recently. I'll have to read through that again. Thanks for the suggestion.

 

[David Violante]

Great post... thank you... I'm appreciating the additional readings too ~

 

[David Violante]

As I got caught in this rabbit hole, I found the following diagram and study. Thank you @Raptor99 for this information. Immensely helpful! I took the information from the study you cited and added the phases to the top of the below study. I believe that they are counting cells as being present, even if not alive, which is why the death phase does not show a decline in cell numbers.



Main phases of wine fermentation. Evolution of the main fermentation parameters during wine fermentation on a synthetic medium containing 200 g/L-1 glucose/fructose and 330 mg/L-1 assimilable nitrogen, with the commercial wine strain EC1118 at 24°C. Dark blue: fermentation rate; light blue: ethanol; red: cell number; green: nitrogen; and purple: sugars.

Marsit, Souhir & Dequin, Sylvie. (2015). Diversity and adaptive evolution of Saccharomyces wine yeast: A review. FEMS yeast research. 15. 10.1093/femsyr/fov067.

 

[BarrelMonkey]

This explains why the overnight starters produce such a quick ferment, as a large portion of the exponential growth takes place in the more ideal environment of the starter. I was certain this was true, but this article confirms it.

And also why you need to carefully build the tirage culture for secondary fermentation in sparkling wines. Even if you're using a rockstar yeast like EC-1118, it won't be happy if you just pitch it into a 10-11% alcohol environment.

Thanks @Raptor99 and @David Violante for the references!

 

[sour_grapes]

Thank you for this, David.

I don't know why the legends and units are missing from the version upthread. (I was perplexed about what the solid dark-blue line was. It is fermentation rate.) Here is the full version, along with the caption:

Main phases of wine fermentation. Evolution of the main fermentation parameters during wine fermentation on a synthetic medium containing 200 g L−1 glucose/fructose and 330 mg L−1 assimilable nitrogen, with the commercial wine strain EC1118 at 24°C. Dark blue: fermentation rate; light blue: ethanol; red: cell number; green: nitrogen; and purple: sugars.​

ETA: That is weird! My newly inserted version is missing part of the legend at the bottom, yet it is visible in the source file...

 

[David Violante]

Paul, I took the original graph and overlayed the timeline at the top of the phases, with the legend descriptions below the color legend. Zero idea why I didn’t include the fermentation rate in the color legend. That was a great find!

 

[David Violante]

So for some reason I’m now up in the wee hours and thought, what better time to find out how yeast know when 1/3 of the sugar is depleted and to move from exponential growth to a stationary phase. It turns out there’s a lot of research on this, potentially from other wee-hour folks.

Multilevel response of the yeast genome to glucose
This article discusses glucose sensing and signaling pathways related to genome transcription and cell regulation, and movement between favoring growth and stationary (fermentation) phases.

Glucose repression in Saccharomyces cerevisiae
Glucose is the primary source of energy for the budding yeast Saccharomyces cerevisiae. [However] When glucose is accessible the yeast prefers a fermentative metabolism despite presence of oxygen, and represses respiration, use of alternative carbon sources as well as gluconeogenesis.

Glucose depletion rapidly inhibits translation initiation in yeast
In S. cerevisiae, the action of glucose as a signaling molecule affects a diverse number of biochemical pathways. Glucose depletion leads to an almost complete inhibition of translation. This inhibition is specific to either glucose or fructose as the carbon source, and it occurs very rapidly after carbon source removal. Readdition of glucose causes a rapid reversal of this inhibition.

@BigDaveK you had a few postings about how much sugars yeast use for growth and metabolism vs. fermentation. It occurred to me to look at the above table and see the sugar reduction calculation and graph during the growth phase as a starting point.

Now I can start my day. LOL

 

[BigDaveK]

@David Violante thanks for those links, I only had 1 of 3.

I found from a couple sources that yeast produce 2.5 gr ethanol for every 6 gr of sugar. (From memory, don't quote me.) I thought I was getting closer to an answer that would give me some level of satisfaction, if even a little. BUT a month or so ago one of my wines opened my eyes to what I think is a bigger question. My ground cherry juice (before sugar) came in at 1.060 and it didn't really taste that sweet. After some research I found that ground cherries have sugar alcohol (polyols), not sugar, and yeast don't use it. I ignored that SG and calculated sugar to add for 1.090, and had a successful fermentation. Because of that I started researching ALL my ingredients and found quite a few discrepancies between the SG and the "official" sugar content of those ingredients. Since then I had 3 wines where my sugar addition was based on ingredient sugar content and not SG, and they were all started between 1.140-1.145, all successful and the alcohol isn't noticeable. So the bigger question I wrestle with now is how much sugar is in my must? And how much alcohol is in my early wines where I put 100% faith in the SG? I now test SG and Brix of my virgin ingredients and the readings can be far apart! There are components, and non-fermentables, affecting the density of the SG and the refraction of the hydrometer. So my current procedure is to research ingredients, take my measurements, and make an educated guess for sugar addition.
This hobby just gets more fun, funner, and funner-er.

 

[winemanden]

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

 

[Raptor99]

@David Violante Thanks for sharing the articles! I haven't had a chance to read them yet, but I was wondering what controls the glucose level. For example, with a flower wine most of the sugar comes from sucrose. Where does the glucose necessary for the exponential growth phase come from? I think that yeast have an enzyme that breaks down sucrose into glucose and fructose. Given that, when will the glucose run out? Is it when the sucrose has all been broken down? Then all that remains is the fructose?

 

[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 imagine it might be a liiiitle different, but I can’t imagine it would be much different. I think other factors may also play a role like temperature, using a nutrient starter like GoFerm, I imagine there are others.

I would think step feeding does indeed extend the stationary phase, as you’re adding more sugar up to the point where they can no longer live in the alcohol environment they’ve created.

 

[David Violante]

@David Violante Thanks for sharing the articles! I haven't had a chance to read them yet, but I was wondering what controls the glucose level. For example, with a flower wine most of the sugar comes from sucrose. Where does the glucose necessary for the exponential growth phase come from? I think that yeast have an enzyme that breaks down sucrose into glucose and fructose. Given that, when will the glucose run out? Is it when the sucrose has all been broken down? Then all that remains is the fructose?

Oh boy… I’m going to have to save this for another wee-hour-a-thon. That’s a great question.

 

[David Violante]

@David Violante thanks for those links, I only had 1 of 3.

I found from a couple sources that yeast produce 2.5 gr ethanol for every 6 gr of sugar. (From memory, don't quote me.) I thought I was getting closer to an answer that would give me some level of satisfaction, if even a little. BUT a month or so ago one of my wines opened my eyes to what I think is a bigger question. My ground cherry juice (before sugar) came in at 1.060 and it didn't really taste that sweet. After some research I found that ground cherries have sugar alcohol (polyols), not sugar, and yeast don't use it. I ignored that SG and calculated sugar to add for 1.090, and had a successful fermentation. Because of that I started researching ALL my ingredients and found quite a few discrepancies between the SG and the "official" sugar content of those ingredients. Since then I had 3 wines where my sugar addition was based on ingredient sugar content and not SG, and they were all started between 1.140-1.145, all successful and the alcohol isn't noticeable. So the bigger question I wrestle with now is how much sugar is in my must? And how much alcohol is in my early wines where I put 100% faith in the SG? I now test SG and Brix of my virgin ingredients and the readings can be far apart! There are components, and non-fermentables, affecting the density of the SG and the refraction of the hydrometer. So my current procedure is to research ingredients, take my measurements, and make an educated guess for sugar addition.
This hobby just gets more fun, funner, and funner-er.

Dave that’s great information and a very intriguing process. I’m interested to see the outcome of a study where one fermentation is based on straight SG as we have been taught and use, and another with changes to sugar content based on your process. The outcome would be taste and alcohol level. Very interesting…

 

[BigDaveK]

I think that yeast have an enzyme that breaks down sucrose into glucose and fructose. Given that, when will the glucose run out? Is it when the sucrose has all been broken down? Then all that remains is the fructose?

Actually yeast have 10 (ten!) enzymes that break down sucrose. Little chemical factories! Yeast are also glucophilic - they prefer glucose to fructose something like 10 to 1. Residual sugar will most probably be mostly fructose.

 

[BigDaveK]

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 don't believe step feeding extends the stationary phase. Most of the yeast reproduction is done in the first day or two, depending on conditions. When I make my dessert wines my first feeding will be around 1.020, well past the stationary phase. I'll feed to about 1.060 and feed a second time when it reaches 1.020 again. Sometimes I feed a third time.