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It is generally advised to leave a yeast starter for at least 24 hours to get optimal yeast growth.

If I only have a few hours, is there any point making a starter from my liquid yeast pack?

Is there any harm done by doing a very short starter, or do I just get a lower cell count than a starter left for the optimal duration?

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A short starter is fine. I often have starters that begin stirring when I start the brewday, so they're only going for 8-10 hours max. With appropriate handling, the risk of contamination can be mitigated and reduced to be negligible.

Due to the small amount of wort, lag time with a vial of yeast is at most a couple of hours (assuming a fresh vial.) Yeast cells bud every 3-8 hours depending upon strain, so you can expect at least a doubling in population, typically more, plus this gets the yeast active, reducing the lag time in primary.

Of course, it's ideal to let the starter run for 24h, but even a third of that is better than no starter at all.

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I prefer to give my starters four or five days. Fermentation is usually done in 24 or 48 hours, but I like to cold-crash the starter so that the yeast falls to the bottom. That way, I can decant the beer off the yeast, and pitch just the yeast. If you only give your starter 24 hours, you're forced to pitch the whole starter into your wort. Not a big deal, I suppose but I prefer to pitch just the yeast.

If you can't let your starter ferment for 24 hours, I'd suggest you skip it entirely. Every time you move your yeast from one place to another, you increase the risk of contamination. If you only have a few hours for your starter, it's unlikely to affect your yeast's cell count, and there's some small risk of infection from the procedure. So you're better off to just pitch directly from the smack pack.

You'll almost certainly be under pitching, unless your beer has a low starting gravity and the yeast is very fresh. You can mitigate the effects of under pitching by oxygenating the wort.

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  • How long do you cold crash for? I usually do 8-12 hours but have wondered if that was long enough. – Matthew Moisen Mar 13 '15 at 9:29
  • @MatthewMoisen 24 -36 hours. – FishesCycle Mar 13 '15 at 13:58
  • Is that because less than 24 hours won't crash all the yeast out of solution? – Matthew Moisen Mar 14 '15 at 3:09
  • That's right. Depending on the yeast 36 hours is usually enough time for the beer to clear. – FishesCycle Mar 14 '15 at 15:19
  • If you limit the amount of malt to only what is needed for whatever degree of multiplication is needed, the yeast will settle out in less than 24 hours – 42- Nov 29 '18 at 23:02
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You can always start your yeast, brew the same day and then pitch the 24hr starter the next day. As long as your sanitation is good your wort will be plenty stable in the fermentor for 24 hours.

I routinely let me lager worts sit in the fermentation fridge over night at the intended pitching temp. Then I pitch the yeast the next day.

I don't think there is any value in doing a 6 hour starter. So my answer is to brew and be careful with sanitation then pitch the next day after you get a 24 hr starter rolling.

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  • You and mdma usually are in closer proximity than this. If 6 hours isn't worth it (I agree), how about 10 hours on a stir plate? – Dale Jan 13 '13 at 0:42
  • I'd revise the last statement in my answer a bit these days. When I know I have really fresh yeast (date stamped on package) I find that pitching it into 500mL of starter wort for 6-8 hours works great to have very live and active yeast. I think my mind has changed over the years that "enough" active yeast is better than the "correct" amount of dormant yeast. Yeast labs seem to be jamming more yeast into their packaging since I wrote this answer too; which seems to help the concept of viability starters vs. growth starters. (which is a dumb set of terms if you ask any micro/biologist. – brewchez Nov 30 '18 at 12:05
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There is no magic number because it depends on your wort volume, OG, ambient temp, stir-plate, etc., but a short starter will benefit you as long as it's over 6 hours or so to ensure at least a couple of budding cycles.

In a time crunch, you definitely cannot cold crash and decant—you'll decant a good fraction of your total cell count; defeating the purpose of the starter and likely doing more harm than good. With that in mind, I would keep the volume of the starter to 1L or less because that wort is going to taste stale. And I would not go much above 1.030 with my starter wort (you won't finish fermentation of it anyway in such a short time).

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