Yeast starter

[pingeyeg]

Hey guys, got a yeast starter question. I have made one yeast starter before, but I'm not entirely sure I did it correctly. For one, how long do I need to leave the yeast starter on the stir plate before letting it ferment? I assume 24 hours is enough time for fermentation on that small amount...? For my first one, I left it on the stir plate for 12 hours and then placed it in the refrigerator till I was ready for it. On the day of brewing, I took it out and let it sit until it was close to room temperature till pitching. Since I wasn't sure about the whole process, I did place it on the stir plate for a minute until the foam started to get close to the top. Like I said, not sure I did this right.

 

[earwig]

I like to let it completely ferment out for a few days, put it in the refrigerator, and then decant the liquid off the top before pitching it. Many others are now just letting it ferment for 24 hours and then pitching everything in it at high krausen into the wort. You are fine either way. There are probably 1000 articles and tutorials on this. Check a few out and then just go with the method you think is best.
The only thing I guess I can add is, in my opinion the yeast need at least 18 hours before cooling or pitching.

 

[diS]

In most cases yeast on stirplate (at normal temperature) will achieve maximum growth in 18-24 hours, depending on vitality, available nutrients and inoculation rate.
Mostly I leave it 24 hrs, you can also take FG reading if you got refractometer to see how well it fermented.

 

[Golddiggie]

Yeast age also impacts how fast a starter will be ready. I've been using some older yeast packs (from the start of the year) and they take about 24 hours before they start to show sign on the stirplate (for the first step). I then cold crash for 12-24 hours, decant and either pitch or add the second (or third) step starter sort to the flask. The second (or third) session on the stirplate usually takes off much faster. I always cold crash and decant my starters. I don't want the spent starter volume going into my beer, just the yeast slurry.

 

[pingeyeg]

So, leaving it on the stir plate during fermentation is not a big deal? I guess that's the whole point of a stir plate huh?

 

[kh54s10]

Check out this video straight from Wyeast:

 

[Golddiggie]

So, leaving it on the stir plate during fermentation is not a big deal? I guess that's the whole point of a stir plate huh?

You want the starter on the stirplate during it's fermentation. Once it's finished, cold crash/chill it so that the yeast flocculates to the bottom to make it easier to get a slurry. It makes it easier to decant the spent wort from the yeast. You can then either pitch that into the brew, or add more starter wort, depending on what you're making and the yeast.

I use yeastcalc.com to figure out the starter sizes, and steps, for my brews. With older yeast packs you can get the cell count needed in two, or three, smaller starters (1.5-3L in size) that would otherwise take a HUGE starter (over 20L).

 

[troyh]

The point of the stir plate is to provide oxygen for the yeast so they get strong and multiply. Fermentation is irrelevant in a starter. In fact, you're not really fermenting a starter as yeast don't produce alcohol when in an aerobic (oxygen) environment, only when they don't have access to oxygen (anaerobic). So, yes, keep it on the stir plate until you are done letting them grow, 12-18 hours.

 

[diS]

In fact, you're not really fermenting a starter as yeast don't produce alcohol when in an aerobic (oxygen) environment, only when they don't have access to oxygen (anaerobic).

Are you sure about this?
Yeast will produce alcohol every time when it got sugars to absorb, no matter aerobic or anaerobic environment. After all, we do aerate wort to increase O2 level after what yeast creates undesirable conditions for other microbes (increase alcohol and decrease pH).

 

[Golddiggie]

Yeast use oxygen in the reproduction phase. This is why we aerate/oxygenate our wort before pitching. The better the O2 infusion, the better/faster the yeast will replicate and then get down to fermenting the wort into beer.

 

[troyh]

Are you sure about this?
Yeast will produce alcohol every time when it got sugars to absorb, no matter aerobic or anaerobic environment. After all, we do aerate wort to increase O2 level after what yeast creates undesirable conditions for other microbes (increase alcohol and decrease pH).

If you were correct, bread would have alcohol. ;-)

Yeast produce CO2 in aerobic and anaerobic conditions. But they also produce water in aerobic conditions and alcohol in anaerobic conditions. You could try drinking your starter and see if you get buzzed to prove me wrong. This, of course, assumes you do not put an airlock on your starter, which you shouldn't do.

We aerate wort only at the beginning to get them to reproduce and get strong cell walls, not to ferment the wort.

 

[pingeyeg]

After the cold break/refrigeration, do you need to allow the yeast to warm up to room temperature before pitching or does it matter? I know when I use a smack pack, I allow the pack to reach room temperature before I shake again and pitch. I assume yes, but it never hurts to ask.

 

[Golddiggie]

After the cold break/refrigeration, do you need to allow the yeast to warm up to room temperature before pitching or does it matter? I know when I use a smack pack, I allow the pack to reach room temperature before I shake again and pitch. I assume yes, but it never hurts to ask.

You want the yeast (or yeast slurry) to be as close to the same temperature as the chilled wort as possible. That doesn't change with the yeast.

 

[earwig]

If you were correct, bread would have alcohol. ;-)

Yeast produce CO2 in aerobic and anaerobic conditions. But they also produce water in aerobic conditions and alcohol in anaerobic conditions. You could try drinking your starter and see if you get buzzed to prove me wrong. This, of course, assumes you do not put an airlock on your starter, which you shouldn't do.

We aerate wort only at the beginning to get them to reproduce and get strong cell walls, not to ferment the wort.

Why does the gravity change then? I think you're wrong.

 

[diS]

Well, this is interesting...
As for gravity, water can also decrease gravity since water"s OG is 1.000, I"m just not sure that starter wont have any alcohol, also most texts that cover starter making suggests proper inoculation rate because of shortening time when yeast will create undesirable conditions for bacteria's, with reducing the pH I assumed that is also an increase of alcohol %.

I am open to new facts about this.

 

[troyh]

Why does the gravity change then? I think you're wrong.

Because the sugars are being processed and removed, lowering the gravity. Gravity is a measure of sugar in solution, not a measure of alcohol.

Read pages 24-25 in "Yeast" by Chris White (founder of White Labs):

"...yeast would rather not make ethanol and they only produce it under special conditions, such as high sugar levels or very low oxygen levels. Yeast get more energy from converting pyruvate into water and CO2 in the presence of oxygen. To make yeast produce ethanol we need anaerobic fermentation."

 

[troyh]

Well, this is interesting...
As for gravity, water can also decrease gravity since water"s OG is 1.000, I"m just not sure that starter wont have any alcohol, also most texts that cover starter making suggests proper inoculation rate because of shortening time when yeast will create undesirable conditions for bacteria's, with reducing the pH I assumed that is also an increase of alcohol %.

I am open to new facts about this.

I believe the proper inoculation rate is more to keep the yeast growing at an optimal rate. Too much or too little results in a less growth. You need to hit the sweet spot.

But yeast are biological, not robots, so they don't follow perfect rules. There may be some small amount of alcohol because, of the billions of cells, some are fooled into making it. This is why open fermentation does produce some alcohol (but that wort is usually added to a closed fermenter to finish the fermentation). The reason we put airlocks on fermenters is to put them in an anaerobic state.

 

[diS]

I googled this topic and here are some interesting highlights:

When oxygen is present, the sugar molecules are broken down aerobically into
carbon dioxide and water, plus the energy (36 ATP) that the yeast uses to grow and reproduce.

In the absence of oxygen, yeast switch to alcoholic fermentation. Alcoholic
fermentation is an anaerobic process, which produces alcohol, carbon dioxide and water.
It does not produce nearly as much energy as aerobic respiration processes; it produces a net gain of 2 ATP.
With alcoholic fermentation, yeast can still get energy from sugar, but less energy is derived from each sugar molecule.

http://www.uri.edu/cels/bio/wetherbee/bio105/lab3.pdf


It seems that yeast do produce some ethanol in anaerobic environment, but it will be consumed via respiration:

Under aerobic conditions a diauxic growth pattern is obtained. Initially, glucose is consumed in a respiro-fermentative metabolism, producing, apart from biomass, also ethanol.
The ethanol, subsequent to glucose depletion, will be consumed via respiration. Thus, the overall catabolic conversion of glucose is to form carbon dioxide and water.

Anaerobically, Saccharomyces has a mono-auxic growth. When glucose is depleted, the growth process stops and the heat and carbon dioxide evolution rates drop to zero.
The amount of heat produced is substantially lower during anaerobic conditions, since a large part of the energy available in glucose is maintained as ethanol.

http://144.206.159.178/ft/1034/72823/1245068.pdf


Seems that propagation yeast in aerobic conditions (starter) creates more energy which results in better yeast growth. Ethanol produced in these environment is respirated later in process.
On the contrary, in anaerobic conditions after glucose is consumed, growth stops and energy available in glucose is produced to ethanol.

 

[DRonco]

Fascinating conversation!

Subscribed.

 

[pingeyeg]

Thanks guys for all your feedback and the yeast lesson. I didn't realize there was so much to learn about yeast. Good stuff!

 

[jmcquesten]

Can someone please explain what is meant by a 3 liter starter? Or any size starter for that matter? I use yeast the pitching calculator (Mr. Malty), and I have made plenty of starters, but am just not sure what is meant by 1 L or 3 L. I typically make a starter with 2 cups water and half cup DME. I cool it to room temperature, then pitch a vial of whatever liquid yeast I'm using. I have been making them in growlers and use foil to cover, shaking as often as possible because I don't have a stir plate. For bigger beers, I've repeated my process a second time to increase it that much more. Obviously, what I'm making doesn't add up to a liter. But, if mr. malty says that a 5 gallon batch at og of 1.080 needs a 2.34 liter starter, what should I be shooting for? Is it 2.34 liters of wort with one vial? If so, do i use more DME? Is it my 2 cup starter stepped up to 2.34 liters? Or, is it 2.34 liters of actual yeast after liquid has been decanted (which I see the least likely and almost impossible on homebrew scale)? I find it hard to believe that anyone is really adding 2 or more liters of liquid, or decanted yeast to a 5 gallon batch of beer.
And another question. How much yeast can be figured when using harvested yeast? I know it depends on a lot, strain, pitch rate, type of beer, etc. But, is there any way for me to guesstimate how much yeast i have in the bottom of a mason jar after I've harvested and washed it?

I have had decent luck with my starters so far, but I'm trying to get a better understanding of the process and how far off my pitching rate is from recommended. Thanks.

 

[troyh]

A 3L starter means 3L of wort that the yeast is pitched into. The easy math is 10g of DME per 100ml of wort but the goal is an OG of ~1.040 for a starter you will pitch into a batch of beer, lower (~1.030) if you're stepping up from a smaller amount of yeast. You should chill and decant the wort so you're pitching mostly slurry.

Slurry contains 1-4 billion cells per milliliter depending on various things. You can estimate 2-2.5 billion/ml if you've taken food care of the yeast. The slurry from the bottom of a fermenter is about 75% yeast, 25% non-yeast (dead yeast, proteins, hop solids) so factor that into your math if reusing yeast. FYI, a lab-created vial of White Labs (and I assume Wyeast) has about 5 billion/ml.

I highly recommend the "Yeast" book; fascinating stuff, in my opinion.

 

[jmcquesten]

A 3L starter means 3L of wort that the yeast is pitched into. The easy math is 10g of DME per 100ml of wort but the goal is an OG of ~1.040 for a starter you will pitch into a batch of beer, lower (~1.030) if you're stepping up from a smaller amount of yeast. You should chill and decant the wort so you're pitching mostly slurry.

Slurry contains 1-4 billion cells per milliliter depending on various things. You can estimate 2-2.5 billion/ml if you've taken food care of the yeast. The slurry from the bottom of a fermenter is about 75% yeast, 25% non-yeast (dead yeast, proteins, hop solids) so factor that into your math if reusing yeast. FYI, a lab-created vial of White Labs (and I assume Wyeast) has about 5 billion/ml.

I highly recommend the "Yeast" book; fascinating stuff, in my opinion.

Thanks. I figured it had to be the wort volume before pitching, but wanted to be sure. I usually make a starter with harvested yeast also to make sure it's active. It seems like i might be really over pitching in that situation. Is over-pitching ever a problem (other than when yeast characteristics, phenols and esters, are desired like in hefes and belgians)?
Another question about harvested yeast... I recently started top-harvesting, by using a blowoff tube into a growler to collect the yeast blowoff at krausen, with pretty good results. I read somewhere that this is the healthiest yeast you can harvest with the added benefit of not having to wash it. Can I figure this yeast the same as fresh yeast straight from White labs? If so, why wouldn't everyone do this? Or do they? It seems to be a great way to harvest yeast and save a bit of money. Are there any downsides to this method, provided sanitation is good?

 

[Golddiggie]

jmcquesten, IF you wash the yeast you'll have far less of anything from the previous batch going into the new batch. Also Mr. Malty has a section for pitching a harvested slurry. You'll need to have some more information (or make some guesses) to get the starter sized properly though.

I'm seriously thinking about harvesting the yeast cake from the batch still in process. That way I should still have some of the Wyeast 1882-PC to use until they offer it up again.

 

[troyh]

Top-cropping is supposed to be the best yeast because it flocculates well – high flocculating yeast clump together and ride the CO2 bubbles to the top, so the best yeast are at the top. It's also harvested sooner so they're healthier than the yeast that sat in the trub for weeks.

Again from the Yeast book, he says top-cropping is so superior to washing that it should be the only way to reuse yeast. The yeast we use today are so good because top-cropping used to be the only way breweries harvested yeast. Yet few people do it because, I think, it's harder to do in a carboy as it requires a special blowoff setup like you have or some kind of vacuum.

 

[earwig]

Because the sugars are being processed and removed, lowering the gravity. Gravity is a measure of sugar in solution, not a measure of alcohol.

Read pages 24-25 in "Yeast" by Chris White (founder of White Labs):

"...yeast would rather not make ethanol and they only produce it under special conditions, such as high sugar levels or very low oxygen levels. Yeast get more energy from converting pyruvate into water and CO2 in the presence of oxygen. To make yeast produce ethanol we need anaerobic fermentation."

Ok, but if you let the starter completely ferment out, and allow the krausen to fall, you agree alcohol is produced right?

 

[Golddiggie]

Ok, but if you let the starter completely ferment out, and allow the krausen to fall, you agree alcohol is produced right?

I wouldn't bank on it, depending on how you process the starter. Using a stirplate, you probably won't. Or you'll get minimal alcohol.

IMO, it's a rather moot point for many of us. I use a stirplate for my starters so that I can make a smaller starter, and get it done faster. Plus, it provides constant aeration and degassing of the starter.

I'm also not about to sample/taste/drink the finished starter. I simply decant the spent starter, down the drain, and then either make more or get the slurry ready for pitching.

 

[troyh]

Ok, but if you let the starter completely ferment out, and allow the krausen to fall, you agree alcohol is produced right?

Yeast don't talk to each other and all agree there is or isn't oxygen and agree to either make alcohol or not. Each cell is making the decision on its own and if a cell doesn't have oxygen available at the time it wants/needs it, it may produce alcohol. A minute later, that same cell may make a different decision and not produce alcohol. In general, they're not producing alcohol in an aerobic environment.

So, yes, there's probably some alcohol. But you should hope it's minimal since it only harms the yeast to produce it and to live in it and that makes your starter less effective when you do want the yeast to produce alcohol.