Making a starter: volume versus gravity

[bdh]

So I was getting ready to make a starter when I realized I'm getting really low on DME (probably only have about 1-2oz left). I was shooting for a 1L starter, but with only 1-2oz of DME that would only give me a gravity in the 1.010-1.020 range.

This got my wondering, if you keep the amount of DME constant, is a gravity of 1.040 optimal to give you the maximum amount of yeast growth, or would you be better off with a larger volume, lower gravity starter.

If you do the starter 12-24 hrs before pitching, it seems like there should still be plenty of unfermented sugars left over, so does that imply the cell count is volume limited? Then again with a low gravity starter I could see funky flavors getting spit out if the yeast are stressed for sugar.

Any ideas?

 

[NordeastBrewer77]

Generally, a 1.040 starter is ideal. To get this, use 1g of DME for every 10 ml of water. So, for your 1L starter, start with 100g of DME, then add water up to ~1L. This will get you right in the area of 1.040.

 

[bdh]

Yes, I know 1.040 is 'ideal'/the standard everyone uses. Right now I only have at most maybe 2oz (~50g) of DME, which will not give a 1.040 1L starter.

My question was more out of general curiosity in the sense that most starter calculator guidelines assume a gravity of 1.040 and then tell you what volume to make (essentially a cell count versus volume curve with a fixed gravity starter). What I was curious about was what the cell count curve looks like if you keep the amount of fermentable sugars the same (i.e. fixed amount of DME) and then vary the volume of the starter (and likewise the starting gravity).

 

[NordeastBrewer77]

You won't produce as much yeast in a lower gravity starter. Not sure of the exact curve, but why not just buy more DME? Also, in a pinch, you could use Malta Goya (the drink in the ethnic foods aisle), it's hopped wort, unfermented. Just boil it, cool, and pitch yeast as normal.

 

[broadbill]

Regardless if you go lower volume to get 1.040 or go with a lower gravity at 1L; less fermentables means lower yeast numbers.

 

[bdh]

Regardless if you go lower volume to get 1.040 or go with a lower gravity at 1L; less fermentables means lower yeast numbers.

Is this really true? Less fermentable sugar less alcohol, sure, but is sugar depletion really what is limiting the cell count you get out of a starter? The general rule of thumb I've always heard is to pitch your starter within 12-24hrs when the yeast are in peak fermentation so they're all charged and ready to go to town on your wort. If they're in peak fermentation, that implies there's still plenty of sugar floating around in the starter. Also, yeast cell count is supposed to top out in a starter after 12-24hrs (http://www.mrmalty.com/pitching.php), which means something besides a lack of sugar (oxygen?) is limiting yeast growth.

A lack of oxygen seems to make the most sense to me since one of the reasons to use a stir-plate is to help oxygenate the starter, and some sites (http://morebeer.com/brewingtechniques/library/backissues/issue2.3/kingtable.html) claim a 1.020 starter gives you more yeast since you can dissolve more oxygen into a lower gravity starter (with the advantage of a 1.040 starter being that it's close to the gravity of most beers so the yeast don't have to adjust as much when they're pitched).

 

[NordeastBrewer77]

Is this really true?

Pretty much, yeah.

 

[ipsiad]

Yeast growth is limited by a lot of factors: oxygen, nutrients, accumulation of waste products (e.g. ethanol), pH, osmolarity, etc... A 2-liter 1.020 wort probably does give you more viable cells than a 1-liter 1.040 wort, because the final concentration of waste products will be lower. Probably not twice as many yeast, but more. However, the yeast are adapted to the environment they are grown in. If you then pitch these yeast into a much higher gravity wort, they may not perform as well as they should due to osmotic shock.

That's the theory anyway, and it makes sense to me. Also, if the yeast companies recommend propagating in a 1.040 wort, there's probably a really good reason for it. That gravity likely strikes the best balance between final cell count, yeast health, and brewing performance.

 

[Denny]

FWIW, most yeast cos. grow in about 1.020 AFAIK.

 

[SpeedYellow]

... However, the yeast are adapted to the environment they are grown in. If you then pitch these yeast into a much higher gravity wort, they may not perform as well as they should due to osmotic shock.

That's the theory anyway, and it makes sense to me. ...

Actually, White & Zainasheff call that a myth in their book Yeast. (pg. 133) Recommending against high-gravity starters (which stress the yeast), they say "Brewers should not believe the myth that yeast become acclimated to high-gravity fermentation from a high-gravity starter."

 

[ipsiad]

FWIW, most yeast cos. grow in about 1.020 AFAIK.

Weird that they recommend we use 1.040 then. Maybe they use continuously fed cultures that maintain 1.020 constantly to keep the yeast in exponential growth phase. Or maybe at the lower gravity, the necessary starter volumes become too big to be practical for homebrewers.

Actually, White & Zainasheff call that a myth in their book Yeast. (pg. 133) Recommending against high-gravity starters (which stress the yeast), they say "Brewers should not believe the myth that yeast become acclimated to high-gravity fermentation from a high-gravity starter."

I think it depends on what is meant by "high gravity." I suspect what they mean by this is don't use a 1.100 starter to grow yeast for a 1.100 beer. It's definitely not a myth that yeast adapt their physiology to the environment they're in (I've studied biology long enough to know that). But there are limits. What I was saying/speculating is that in a low stress environment, such as a low gravity wort, yeast won't produce as much trehalose (for example) as they would in a moderate gravity wort, because they don't need to. Take those yeast and pitch them directly into a high gravity wort, and they may not tolerate it as well as yeast that were grown in a moderate gravity wort.

 

[helibrewer]

Volume is a big factor for starter growth, you want 25-50 million cells per milliliter for your starting population. That's why the yield, when using a single smakpak is higher with a 2L starter (50 mil/ml) versus a 1L starter (100 mil/ml). Yeastcalc.com has growth curve graphs that will show you the volume effects...it's all about the initial cell concentration.

 

[Slowfro]

I've always had the 1.040 number in my head as the rule of thumb from reading something somewhere some time ago, but when I first started making starters after washing yeast (many many batches ago) I went off the simple round figures of 1/2 cup of DME in 1L water and it's worked great for me. Doing the math that gives you about a 1.022 starter.

 

[bdh]

It's definitely not a myth that yeast adapt their physiology to the environment they're in (I've studied biology long enough to know that).

Haha, very true... In fact they adapt enough to fill 72 pages worth of a microbiology review article (as of 10 years ago) (http://www.ncbi.nlm.nih.gov/pubmed/12040128).

From a practical brewing standpoint I wonder how much of an impact this has on flavor. Under-pitching is definitely noticeable, but pitching yeast from a 1.040 starter into a 1.100 beer would be a pretty large shock as well regardless of how many yeast you threw in. It would be an interesting experiment to do a split batch on a high gravity beer with a 1.040 starter in one fermenter and a high gravity starter in the other fermenter (perhaps doing a multi-stage starter to bump up the gravity in stages).

 

[Denny]

Haha, very true... In fact they adapt enough to fill 72 pages worth of a microbiology review article (as of 10 years ago) (http://www.ncbi.nlm.nih.gov/pubmed/12040128).

From a practical brewing standpoint I wonder how much of an impact this has on flavor. Under-pitching is definitely noticeable, but pitching yeast from a 1.040 starter into a 1.100 beer would be a pretty large shock as well regardless of how many yeast you threw in. It would be an interesting experiment to do a split batch on a high gravity beer with a 1.040 starter in one fermenter and a high gravity starter in the other fermenter (perhaps doing a multi-stage starter to bump up the gravity in stages).

It's much more important to pitch a large quantity of healthy yeast. The yeast will be healthier in a lower gravity starter. I can tell you from much experience that there's no problem pitching a 1.030 starter into 1.100+ wort, if you've grown enough healthy yeast.

 

[bdh]

It's much more important to pitch a large quantity of healthy yeast. The yeast will be healthier in a lower gravity starter. I can tell you from much experience that there's no problem pitching a 1.030 starter into 1.100+ wort, if you've grown enough healthy yeast.

Right, I was more just curious about if you had two starters with essentially the same number of healthy yeast but one was a low gravity starter and one was a higher gravity starter if you could notice a difference between the two batches. This is all purely speculation, but I could see two reasons why higher gravity starters don't give you as many healthy yeast:

1) Yeast just can't be that healthy in higher gravity wort.
2) The osmotic shock from moving yeast from a low gravity vile to a high gravity starter stresses out/kills lots of your yeast and gives you a smaller number of healthy yeast.

If it's the osmotic shock that's making unhealthy yeast, then making a series of increasingly higher gravity starters gives the yeast time to adapt and makes the shock of going into your high gravity wort less. If, instead, yeast are just never all that healthy in a high gravity wort then yeah, there's no point in trying to do a higher gravity starter - just stick with a lower gravity starter and pitch as many healthy yeast as possible.

Anyway, I'm sure the yeast co's have probably all looked at this and decided the lower gravity starter is better, but I'm still kind of curious to try.

 

[Denny]

If it's the osmotic shock that's making unhealthy yeast, then making a series of increasingly higher gravity starters gives the yeast time to adapt and makes the shock of going into your high gravity wort less. If, instead, yeast are just never all that healthy in a high gravity wort then yeah, there's no point in trying to do a higher gravity starter - just stick with a lower gravity starter and pitch as many healthy yeast as possible.

Anyway, I'm sure the yeast co's have probably all looked at this and decided the lower gravity starter is better, but I'm still kind of curious to try.

You seem to be making the assumption that there is a shock from yeast going into a higher gravity wort. That's the thinking that was around 15 years ago, but it's been pretty much discounted.

Info from mrmalty, including a quote from Dave Logsdon, former owner of Wyeast...

"Q: If I'm making a high gravity beer, shouldn't I make a high gravity starter so the yeast become acclimated?

No. In general, starter wort should be between 1.030 and 1.040 (7 - 10°P). If you're trying to revive a stressed yeast, like culturing up yeast from a bottle conditioned beer or from an old slant, use a lower gravity starter wort around 1.020 (5°P). Lower gravity starters are easier on the yeast, but result in less growth. High gravity starters result in more growth, but are more stressful for the yeast. Exceeding the higher end of the range is stressful on the yeast and should be avoided.

Logsdon says, "Generally, you'd use the lower end of that range [1.020 SG, 5°P] for coming off a plate or slant or very old yeast. Yeast don't get used to a high gravity environment, and the high osmotic pressure can really stress the yeast. Don't forget, you want to increase healthy cells in a starter more than you want to increase the number of unhealthy cells."

http://www.mrmalty.com/starter_faq.php

 

[TrubHead]

In the few times washing and reusing yeast (new brewer here), I've observed some washed yeast strains starting quickly and others not. Could the OG of the harvested yeast be a factor in how "resilient" (for lack of better wording) they are for the next starter? I'm having particular issue with S-04.

 

[Denny]

I think it has more to do with the strain of yeast. For instance, some hefe strains don't repitch well. Maybe S04 is similar.

 

[bdh]

You seem to be making the assumption that there is a shock from yeast going into a higher gravity wort. That's the thinking that was around 15 years ago, but it's been pretty much discounted.

Well there's definitely going to be a shock of some sort. Rapidly increasing the osmotic pressure difference across the cell membrane will cause the yeast to lose a lot of water in a hurry. The yeast can compensate to a degree by increasing intracellular salt concentrations, changing the makeup/number of ion channels, glucose transporters, etc... but all that takes time.

I agree that just tossing a tube of yeast into a high gravity starter isn't the best idea since now you're introducing this shock earlier before you even grew up a large yeast population in the first palce, but what I want to know is whether you can (and if you can whether the effect is enough to be noticeable in the finished beer) limit this shock to an extent by slowly increasing the gravity of the starter. At some point though you're going to hit a gravity where the yeast just aren't happy no matter how long you give them to adapt.

 

[TrubHead]

I think it has more to do with the strain of yeast. For instance, some hefe strains don't repitch well. Maybe S04 is similar.

I'm thinking that too. Might see how the washed S04 does with more time in the starter.

 

[TrubHead]

Well there's definitely going to be a shock of some sort. Rapidly increasing the osmotic pressure difference across the cell membrane will cause the yeast to lose a lot of water in a hurry. The yeast can compensate to a degree by increasing intracellular salt concentrations, changing the makeup/number of ion channels, glucose transporters, etc... but all that takes time.

I agree that just tossing a tube of yeast into a high gravity starter isn't the best idea since now you're introducing this shock earlier before you even grew up a large yeast population in the first palce, but what I want to know is whether you can (and if you can whether the effect is enough to be noticeable in the finished beer) limit this shock to an extent by slowly increasing the gravity of the starter. At some point though you're going to hit a gravity where the yeast just aren't happy no matter how long you give them to adapt.

Think this is why when brewing those much higher gravity beers, more sugars are introduced after the OG has dropped a bit. Think each strain has it's limits and peculiarities.

 

[junior]

In the few times washing and reusing yeast (new brewer here), I've observed some washed yeast strains starting quickly and others not. Could the OG of the harvested yeast be a factor in how "resilient" (for lack of better wording) they are for the next starter? I'm having particular issue with S-04.

This may be off topic, but how much of the washed yeast slurry do you normally use for a 2L starter?

 

[TrubHead]

This may be off topic, but how much of the washed yeast slurry do you normally use for a 2L starter?

Current equipment is limited to smaller batches (3.5 gallons max) so don't need a big starter. Used two 12 oz beer bottles of washed yeast which was about 3/8 - 1/2 inch in height for a 750 ml starter.

 

[junior]

Current equipment is limited to smaller batches (3.5 gallons max) so don't need a big starter. Used two 12 oz beer bottles of washed yeast which was about 3/8 - 1/2 inch in height for a 750 ml starter.

Trub, Thank's for the reply, I have been trying to get an answer to this question for a long time. Once again thank's for the info.

 

[TrubHead]

Trub, Thank's for the reply, I have been trying to get an answer to this question for a long time. Once again thank's for the info.

Glad to assist. Don't have a stir plate so swirled the flask every couple hours or so and in less than 36 hrs the krausen was foaming and lots of bubbles could be seen rising.

 

[junior]

Glad to assist. Don't have a stir plate so swirled the flask every couple hours or so and in less than 36 hrs the krausen was foaming and lots of bubbles could be seen rising.

Trub, Thank's, just ordered a fan to make a sir plate.