Yeast "colony" - does it need to stay intact in some way?

[Brandon M]

I'm making mead for the first time, time, and a lot of pages recommend fairly vigorous shaking or stirring until it gets below a certain SG and the yeast switch from multiplying to conversion of sugars to alcohol.

When people use the phrase "yeast colony," that implies to me a specific location within the larger batch of must, containing a high number of yeast cells all living happily together. This makes me nervous about really stirring up to oxygenate .

Is there any reason to let the yeast be undisturbed - so that a colony within the larger volume of must remains intact? For example, does a lot of the fermentation happen in the lees at the bottom? Or is this generically a term to the yeast spread throughout the entire volume of the must liquid? Just trying to figure out the science of it all.

 

[ChuckD]

The yeast are in suspension spread throughout the must, in the cap, and on the bottom. The lees have a lot of dead (dormant?) yeast cells as well. You need to stir it up during the first third (at least) of the fermentation cycle because this is when yeast are multiplying. They need oxygen for this process.

 

[winemaker81]

Adding on to @ChuckD's comment, the protocol I'm currently using is to make an overnight yeast starter. This gives the yeast the opportunity to form a larger initial colony in an environment that is more to the yeast's liking. When inoculating, the protocol calls for swirling the starter to mix up any sediment, then gently pouring the starter down the inside of the fermenter, so it spreads as little as possible.

The yeast is now in a food-richer but environmentally less friendly environment, and the yeast will reproduce better if the starter doesn't spread a lot.

However, after 24 hours fermentation should be well underway, so begin stirring or punching down, as Chuck said.

There are numerous protocols for starting fermentation; however, I've been using this one for over 2 years and every ferment has taken off quickly.

 

[Rice_Guy]

When people use the phrase "yeast colony," that implies to me a specific location within the larger batch of must, containing a high number of yeast cells all living happily together. This makes me nervous about really stirring up to oxygenate . - - Is there any reason to let the yeast be undisturbed

Yeast colony is an unusual term for wine making. Colony is usually applied to organisms which form a mat such as mold or Acetobacter, ,,, both of which require oxygen so they float on the surface of a medium or a wine. When I look at yeast under the microscope they appear as individuals or possibly a mother cell with a daughter budding off.

The graphic in David’s message below is a picture of what happens in a fermentation. In the scale of a home fermentation, one to ten gallons the population will be relatively uniform throughout the carboy. Yes yeast is heavier than wine or beer so there is a slightly higher concentration the lower one goes in the carboy/ tank. In a factory setting we will keep the mixture suspended via nitrogen bubbles sparged in the bottom of a tank or via mechanical agitation. As senescence happens the separation is high enough that we see a dust layer in a carboy called fine lees. On a one week old basis the yeast lees will be substantially alive and can be used to start another fermentation as with Skeeter pee or a beer. ,,, You should expect some live yeast in suspension under six months therefore it is normal for wineries to filter any time they back sweeten. Long hold times as six months or a year allow the yeast to starve or metabolic byproducts like alcohol poison the yeast.

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.

View attachment 96883

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.

Calling yeast a colony forming organism is technically incorrect! Check the author’s qualifications. They probably never took a microbiology course or looked through a microscope.

 

[Hazelemere]

I'm making mead for the first time, time, and a lot of pages recommend fairly vigorous shaking or stirring until it gets below a certain SG and the yeast switch from multiplying to conversion of sugars to alcohol.

When people use the phrase "yeast colony," that implies to me a specific location within the larger batch of must, containing a high number of yeast cells all living happily together. This makes me nervous about really stirring up to oxygenate .

Is there any reason to let the yeast be undisturbed - so that a colony within the larger volume of must remains intact? For example, does a lot of the fermentation happen in the lees at the bottom? Or is this generically a term to the yeast spread throughout the entire volume of the must liquid? Just trying to figure out the science of it all.

leave yeast undisturbed at the very start of fermentation even from a starter. Pour on top of a must so they can reproduce with exposure to oxygen and then each day stir them into the must and more. If they are super active after 24 hours your can stir them in even more. Usually after 48 hours you are good to go with vigorous mixing especially if you add nutrient at the start especially nutrient containing vitamins that the yeast seem to love e.g. RC212 loves nutrient.

 

[Brandon M]

Thanks, all. To summarize the various answers:

1) "Colony" is a misnomer: commonly used, but factually incorrect. If someone says "colony," just grin and ignore it. They mean well.

2) The yeast are everywhere in the must. Not clustered; maybe higher concentration at the bottom if the bubbling has settled down, but generally everywhere.

3) It probably makes sense NOT to stir the rehydrated yeast into the must - leave them up top with the O2 for a while, with conditions closer to their initial rehydration "nursery," and they'll distribute themselves as they begin to multiply.

4) Once they're kicked off and happy, stirring or shaking is not bad at all, and helps (until they get past the initial reproduction stage at least).

5) (Not explicitly said here, but I gather this from other posts) Don't stir O2 into the must once the first third or so of the sugars have been consumed. The yeast are mostly past the multiplication phase where O2 is needed; oxygenation will begin to cause oxidation of the ethanol and lead to lower quality results.

Did I get all that basically correct?

 

[Ohio Bob]

5) (Not explicitly said here, but I gather this from other posts) Don't stir O2 into the must once the first third or so of the sugars have been consumed. The yeast are mostly past the multiplication phase where O2 is needed; oxygenation will begin to cause oxidation of the ethanol and lead to lower quality results.

You do want to push the cap down so it doesn’t grow spoilage mechanisms.

 

[David Violante]

Brandon, yes, well done!

Another step to a healthy fermentation I like to do occurs when I’m ready to pitch the yeast starter. I will slowly move the conditions of the starter to those of the must. I will add a small amount of the must to the starter, usually not more than a quarter to a third the current volume of the starter, and let it sit. I will repeat the process a few times, and then pitch the whole thing as a ‘colony’ into the must. It will disperse on its own and when there are active signs of fermentation I’ll stir it all up to get uniformity, oxygenation, some CO2 release, and cap punch down.

 

[winemaker81]

5) (Not explicitly said here, but I gather this from other posts) Don't stir O2 into the must once the first third or so of the sugars have been consumed. The yeast are mostly past the multiplication phase where O2 is needed; oxygenation will begin to cause oxidation of the ethanol and lead to lower quality results.

Points #1-4 are well written, but this one is off. As Bob said, you need to punch down the cap to avoid spoilage organisms growing on it, and this applies to juices as well.

During fermentation, O2 is not a problem. During punch down/stirring, it's impossible to avoid introducing O2, so don't worry about it.

The wine is safe from O2 while heavily outgassing, but once the outgassing slows down or stops, O2 then becomes a serious issue. How do we know where the dividing line is?

The short answer is "we don't", so we take precautions, such as eliminating excess headspace shortly after fermentation ends, and adding K-meta, which binds with O2 and renders it harmless.

 

[winemaker81]

Yeast colony is an unusual term for wine making. Colony is usually applied to organisms which form a mat such as mold or Acetobacter, ,,, both of which require oxygen so they float on the surface of a medium or a wine. When I look at yeast under the microscope they appear as individuals or possibly a mother cell with a daughter budding off.

It's interesting -- Scott Labs, AWRI, and Lallemand don't use the term "colony". But it seems like everyone else does -- various research papers, nature sites, etc. Correct or not, "yeast colony" is a commonly used term.

 

[Brandon M]

The short answer is "we don't", so we take precautions, such as eliminating excess headspace shortly after fermentation ends, and adding K-meta, which binds with O2 and renders it harmless.

Does K-meta kill yeast or bacteria? Or is it purely an oxidation prevention?

 

[winemaker81]

Does K-meta kill yeast or bacteria? Or is it purely an oxidation prevention?

K-meta may kill or stunt non-commercial yeast and other microbial life, and it renders many contaminants harmless by combining with them. Anti-oxidant is just one part that it plays.

 

[Brandon M]

Points #1-4 are well written, but this one is off. As Bob said, you need to punch down the cap to avoid spoilage organisms growing on it, and this applies to juices as well.

During fermentation, O2 is not a problem. During punch down/stirring, it's impossible to avoid introducing O2, so don't worry about it.

The wine is safe from O2 while heavily outgassing, but once the outgassing slows down or stops, O2 then becomes a serious issue. How do we know where the dividing line is?

The short answer is "we don't", so we take precautions, such as eliminating excess headspace shortly after fermentation ends, and adding K-meta, which binds with O2 and renders it harmless.

So maybe this is better?

5) Once the first third or so of the sugars have been consumed, intentional oxygenation may be harmful. Punching down a fruit cap is still necessary - but not oxygenation. The yeast are mostly past the multiplication phase where O2 is needed, and moving into the anaerobic fermentation phase; oxygenation will begin to cause oxidation of the ethanol and lead to lower quality results.

 

[winemaker81]

So maybe this is better?

5) Once the first third or so of the sugars have been consumed, intentional oxygenation may be harmful. Punching down a fruit cap is still necessary - but not oxygenation. The yeast are mostly past the multiplication phase where O2 is needed, and moving into the anaerobic fermentation phase; oxygenation will begin to cause oxidation of the ethanol and lead to lower quality results.

IMO, and maybe only IMO, no.

It's overthinking the subject and for most beginners, it's an unnecessary complication that produces nothing more than unnecessary worry. There's a lot of misinformation about O2 and winemaking, and on a regular basis we have people concerned about racking their wine because exposure to air will immediately ruin it. Read through the Beginners forum -- you'll find a fair number of initial posts that start with something like, "I did X. Is my wine ruined? Should I throw it out?"

Are you going to do anything different because the yeast no longer needs extra O2, or are you just going to punch down/stir as usual? If something is NOT changing your actions, it's not something to worry about.

Again, once fermentation is complete, O2 becomes a serious enemy to avoid. I say "avoid" because most things in winemaking work best in an avoidance situation -- once you have to fix something, it's a lot more difficult or even impossible to mitigate.

Note that K-meta is both a preventative and a cure, as much as a cure will work in a given situation.

 

[cmason1957]

So maybe this is better?

5) Once the first third or so of the sugars have been consumed, intentional oxygenation may be harmful. Punching down a fruit cap is still necessary - but not oxygenation. The yeast are mostly past the multiplication phase where O2 is needed, and moving into the anaerobic fermentation phase; oxygenation will begin to cause oxidation of the ethanol and lead to lower quality results.

I'm not sure that's any better, I think (and it's just my opinion) that O2 is needed all throughout the ferment, maybe less as we go. but newly budded yeast, which happens throughout the entire process needs that oxygen to keep going. Now punch-downs should not be so vigorous as you get nearer to completion, but only becasue it doesn't take as much effort later on. It's after fermentation that we need to worry more about O2, not during.

 

[BigDaveK]

Just a couple points -

I'm making mead for the first time, time, and a lot of pages recommend fairly vigorous shaking or stirring until it gets below a certain SG and the yeast switch from multiplying to conversion of sugars to alcohol.

Yeast are amazing creatures and bullies when it comes to surviving. They don't at some programmed point switch from multiplying to ethanol production. Because of the Crabtree Effect the bloodthirsty little guys start making alcohol very quickly to kill competitors and make the environment as inhospitable for interlopers as possible.

When people use the phrase "yeast colony," that implies to me a specific location within the larger batch of must, containing a high number of yeast cells all living happily together. This makes me nervous about really stirring up to oxygenate .

If there's a yeast colony you're living in it. They're everywhere.

Kudos for your curiosity and thirst for knowledge but I agree it's very easy to overthink.

 

[sour_grapes]

I tend to think that "colony" is a fine term to use. It's just that the colony is the same size and shape as my fermentation vessel!

 

[vinny]

Brandon, yes, well done!

Another step to a healthy fermentation I like to do occurs when I’m ready to pitch the yeast starter. I will slowly move the conditions of the starter to those of the must. I will add a small amount of the must to the starter, usually not more than a quarter to a third the current volume of the starter, and let it sit. I will repeat the process a few times, and then pitch the whole thing as a ‘colony’ into the must. It will disperse on its own and when there are active signs of fermentation I’ll stir it all up to get uniformity, oxygenation, some CO2 release, and cap punch down.

I make my starters from my must. I take about a cup and water it down around 50% and pitch the yeast to that. Just mentioning it for interests sake.

 

[winemaker81]

I make my starters from my must. I take about a cup and water it down around 50% and pitch the yeast to that. Just mentioning it for interests sake.

the starter methods described in this thread have one important thing in common -- they all work.

Something to consider is that there's no reason to pick one method and stick with it. Try different ideas and go with what is best liked. Or keep switching around. Also consider that the method we're most comfortable with is probably the best one to use.

 

[Hazelemere]

Thanks, all. To summarize the various answers:

1) "Colony" is a misnomer: commonly used, but factually incorrect. If someone says "colony," just grin and ignore it. They mean well.

2) The yeast are everywhere in the must. Not clustered; maybe higher concentration at the bottom if the bubbling has settled down, but generally everywhere.

3) It probably makes sense NOT to stir the rehydrated yeast into the must - leave them up top with the O2 for a while, with conditions closer to their initial rehydration "nursery," and they'll distribute themselves as they begin to multiply.

4) Once they're kicked off and happy, stirring or shaking is not bad at all, and helps (until they get past the initial reproduction stage at least).

5) (Not explicitly said here, but I gather this from other posts) Don't stir O2 into the must once the first third or so of the sugars have been consumed. The yeast are mostly past the multiplication phase where O2 is needed; oxygenation will begin to cause oxidation of the ethanol and lead to lower quality results.

Did I get all that basically correct?

If you are fermenting juice in a carboy from a white wine or red from pressing then you can aerate mid ferment e.g. SG 1020 to 1030 is good without oxidation so you can bentonite the white to remove protein and keep the red fermentation active. Tannin in the red protects it from oxidation. Sulphite in the white protects it from oxidation. Bentonite strips all sulphite so once you rack off of bentonite sediment you have to resulphite. If you are fermenting red wine grapes in a primary fermenter you need to stir them up at least once a day top to bottom to prevent hydrogen sulphide formation due to absence of oxygen. Once the wine is cleared of all slude after pressing e.g. ~SG 1.000 and maybe one extra racking you can leave alone at room temperature to finish MLF and then rack and sulphite to prevent contamination by aerobic bacteria or molds. The wine on the left is uncrushed hand destemmed Cabernet Sauvignon at SG 1.060 started last Saturday. The wine on the right is uncrushed hand destemmed Petit Verdot at SG 1.050. It has more liquid because the berries are softer than the Cabernet. This is RC212 with nutrient containing vitamins. The ferment is strong and health. I stir the must once a day in the morning.