Splitting Yeast?

Quick yeast question. I fairly new to brewing. I am doing a small batch of an amber ale (2.5 gal) for various reasons. I have a wyeast packet that I will use for this beer. Can I use only half of it in the wort and save the other half in a sanitized mason jar in the fridge? If so, how long will the yeast remain viable for use in a later batch? And will that "half packet" of yeast be sufficient for a full 5 gallon wort later? Thanks for the insight.

Check with MrMalty.com's Pitch Rate Calculator to see how much yeast you need, chances are it's the whole pack or more. What you can do is make a starter, which you should do anytime you use liquid yeast, that's twice the size that MrMalty calls for. After it's done, chill and decant the liquid, pour half the slurry into a sanitized jar to fridge and save for later, and pitch the other half of the slurry into your batch. I do this quite a bit to get the most out of each pack of yeast.

I would say pitch the whole thing--it will make sure you have plenty of yeast for your fermentation, and you can always buy another yeast packet, or harvest your yeast and reuse on the next batch. Otherwise, you could make a starter, (See this thread), use half of it in this batch and save the rest for the future. I think John Palmer says you can store yeast in the fridge for up to a couple of months, although I've never reused yeast myself after longer than 2-3 weeks. Does anyone have thoughts on how long you can store yeast in the fridge before it goes bad?

NordeastBrewer77 said:

After it's done, chill and decant the liquid, pour half the slurry into a sanitized jar to fridge and save for later, and pitch the other half of the slurry into your batch. I do this quite a bit to get the most out of each pack of yeast.

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Just realized that I do the same thing but in a different way. I use half a vial of yeast to make the necessary starter and save the other half of the vial for a future starter.

Your way sounds like it'd take less time since you're working with more yeast up front and splitting it in half later.

sidepart said:

Just realized that I do the same thing but in a different way. I use half a vial of yeast to make the necessary starter and save the other half of the vial for a future starter.

Your way sounds like it'd take less time since you're working with more yeast up front and splitting it in half later.

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Six in one hand...... I just find it easier since I wash and save yeast in jars anyway. I also usually use Wyeast, so using half a pack would be a PITA. When I get a new pack of a yeast I use often, I take the yeast I'm saving and make a ~2L starter so I can save a few jars. Combining that with washing some yeast, which I usually only do with dry strains, one can make a few bucks spent on yeast go a really long way.

So one option for me would be to pitch the entire packet, and then would I be able to simply brew another batch of the same beer and ferment it on the yeast cake from this one?

Not necessarily the same beer, although you certainly could. Depending on the yeast strain you can brew several different styles. For ex, I use White Labs WLP007 Dry English Ale yeast for ESBs and IPAs...you could also use it for ambers, stouts, etc. Usually you want your yeast strain to match your beer style--a dry strain with higher attenuation for a drier beer, an English yeast strain for an English beer style, etc. But there's no reason you can't make something different off of the same yeast cake.

sidepart said:

I use half a vial of yeast to make the necessary starter and save the other half of the vial for a future starter.

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I do the same thing with the White Lab vials and have used the other half of the vial 2 months later without any obvious problem. If your LHBS has decent turn-over you should be able to pick up vials with expiration dates 2-3 months away. I just bought one yesterday (Sept 12th) that is good until December. I'll use half of it this weekend and the other half... sometime before December.

EDIT: I also do 1 gallon size test batches and split the vials into 1/4ths for those.

JStew said:

So one option for me would be to pitch the entire packet, and then would I be able to simply brew another batch of the same beer and ferment it on the yeast cake from this one?

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This is actually the easiest option if you're brewing a beer that you'd like to use the same yeast for. Right now I'm using WLP007 for a few brews. I split a vial into two yeast batches. The first made an Oktoberfest, a Surly Bender clone and (soon) a Russian Imperial Stout all on that same cake. The other half of the vial I'm going to use for a Wet Hop IPA and a Milk Stout.

People have told me that you probably don't want to brew a dark beer and then pour a light beer onto the cake. Similarly if you get a lot of hop trudge, I've been told that it may not be a good idea to rack a malt forward beer onto a cake that was originally used for an IPA. I don't really have this issue since I pour my beers through a strainer into the bucket.

Anyway situations like these prompt people to actually save that yeast cake and wash it for later...but I haven't really had the patience for this. I have 2 jars in my fridge right now...haven't really been excited test and see if they'd ferment honestly. Good luck though. Saving money on yeast is fun. Pretty soon you start looking like some kind of scientist...with Erlenmeyer Flasks, stir plates, petri dishes and microscopes.

Your best bet is to wash the yeast from this batch, and use the right amount of yeast for your next batch using that yeast. Pitching on a yeast cake isn't the best habit to get into.

BigRob said:

Your best bet is to wash the yeast from this batch, and use the right amount of yeast for your next batch using that yeast. Pitching on a yeast cake isn't the best habit to get into.

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Agreed. An entire cake is a gross overpitch for most batches of beer. Overpitching can cause issues like thin mouthfeel, yeast-y flavors, among other things. Your best best is to always use a pitch rate calc like the one I linked above to gauge how much yeast you use per batch.
When reusing yeast from a batch, it's best to wash part or all of the cake and use some washed yeast to either pitch or make a starter. Mr Malty has a calculator that can help you with starter size and with how much washed slurry to use per batch.