reusing yeast

[Brewhemoth]

Hey guys, I have some questions about what to do next.

after primary fermentation, I racked off into a secondary. left a little bit of beer on top of the yeast, swirled it around and funneled into sanitized screw top glass bottles. I have a few of them. the continue to ferment for another day or two.

question is on re-pitching this. I have heard that washing yeast is not ideal. I have read about scooping off layers of yeast (keeping the middle layer and reusing only that).

can i simply swish the whole bottom layer in my flasks back into solution and re-pitch? do i need to stratify it somehow? how do i know how much to pitch (i don't quite understand that Mr. Malty settings for re-using yeast on the pitch rate calculator).

any suggestions on the approach to take would be appreciated

 

[dinnerstick]

i would just use it as it is, as long as you are confident that you were really clean. it's an easy time to pick up and propagate wild yeast or other unwanted critters, or to have harvested more trub and break than yeast, so until you have harvested a few times and can do it with your eyes closed (not to suggest that it's rocket science; it's easy), keep a close watch on the next batch for signs of infection or poor yeast health. the mrmalty calculator is pretty straightforward. it will never be very precise since you don't know how much of your yeast cake is yeast, but it guides you toward a good starting point. estimate how much yeast cake you have by volume. just get a rough estimate from the jar or whatever the yeast is in: 50 ml, 200 ml, whatever. go to the repitching from slurry tab, leave the sliders (concentration and non-yeast) where they are on the calculator. fill in your batch size and gravity, and it will tell you how many mls of your yeast cake to use. pretty easy.

 

[LLBeanJ]

Washing yeast is okay (yes, there are some concerns regarding growth and yeast health, but I wouldn't be too worried about it until you start getting into multiple generations of washing), but it's more of a hassle than it's worth, in my opinion. In my estimation, it's better to pitch straight slurry or split starters made from clean yeast (I.e., pitch most of a starter into a brew and save off a portion of it for a future starter, which can be repeated ad infinitum).

How long will it be between harvesting and pitching the slurry? If a couple of weeks or less, just pitch it straight. Use the default settings for pitching from slurry that mrmalty provides and pitch just what you need. Unless you have a reason (spoiler alert: you don't), there's no need to deviate from the default settings. They may not be right on, but they will be plenty close enough.

If it's been longer than 2 or 3 weeks since you harvested the yeast, I'd still pitch straight if you have enough according to mrmalty, but if you don't then you should make a starter to increase the cell count.

There are some things to consider when pitching straight slurry, however: The idea is to brew less flavorful lighter beers and pitch the slurry from that onto more flavorful or darker beers, but there is a bit of leeway there. For example, it's okay to pitch slurry from a low-hopped amber onto a moderately or highly-hopped pale or dark beer, but I wouldn't use slurry from a big stout or porter into a blonde ale as some of the roastiness will likely carry over. Same for slurry from an IPA, as some of the hop flavor will carry over, unless you want hop flavor, then it's okay. It's not an exact science, so just be cognizant of what you're doing and how flavors from slurry might carry over into the next brew. Best scenario is to pitch slurry from lighter beers to darker and/or lightly hopped to more hopped. I reuse slurry from time to time, but more often I just split starters so that I'm pitching fresh, clean yeast into every brew.

 

[Sbarnard80]

Very helpful advice (I hope). Rationale makes sense. I just stored my first yeast cake a few weeks ago from a session IPA I did and was wondering about details of having to wash etc etc. I grabbed a good bit of it and was very careful about sanitation. Will use mrmalty to check out how much to use and do a starter and give it a shot with probably another batch of the same thing. Will watch the fermentation closely and be ready to pitch more if needed. Interested to see how this comes out. Thanks

 

[masonsjax]

Pitching yeast from a roasty beer into a lighter one is fine. Roast flavors wont carry over unless you left a lot of the beer in there, I do it often enough. The problem is when you make a really big beer like a barleywine or RIS that could leave you with seriously tired stressed yeast. I plan those beers for the end of a colony's existence in my pipeline.

 

[masonsjax]

Also, you don't necessarily need to harvest into new jars. You can reuse the fermenter by just dumping out or harvesting all but the amount of yeast you need for the next batch.

 

[Brewhemoth]

thanks for chiming in guys! so shall i dispose of most of the beer sitting on top of the yeast bed that has formed in my jars and pitch just the slurry?

 

[kh54s10]

You need to read up. In the middle of your post you described using the middle layer. This in essence IS yeast washing. Many people wash yeast as a normal part of their procedure.

When you look at mrmalty, the slurry part tells you how much of a saved yeast cake will give you the proper amount of yeast cells for your batch. You have to decide how dense it is. If you left a lot of beer on top and swirled it in to loosen the cake that would be a thin slurry. Also if you used pellet hops in the fermenter then your non yeast percentage would be high.

If you plan to pitch onto the yeast cake of a recently finished beer you will not need the whole cake. 1/3 to 1/2 is the generally accepted amount.

As already discussed, If you do not wash your yeast some of the beer flavor from the prior batch will be introduced into the new beer.

Another consideration on how much slurry to pitch is how long it has been since you saved it. The viability of the yeast starts to decrease as soon as fermentation has finished.

BTW, If your fermentation was finished when you transferred to secondary (as it should have been) you should have had no further fermentation, probably just co2 coming out of solution with the agitation and temperature changes.

 

[smccarter]

If you plan to pitch onto the yeast cake of a recently finished beer you will not need the whole cake. 1/3 to 1/2 is the generally accepted amount.

That's what I've done with my last 3 batches. I'll be doin the same for the next two as well. I like the idea of re-using yeast, but harvesting and washing yeast is such a pain in the azz. I simply racked to keg, then siphoned off about 1/2 to 2/3rds of the yeast cake, then pitched directly onto what is left.

What I did though, was to brew 5 batches of beer using new yeast, then brewed the same 5 beers pitching the same beer onto the yeast cake. This will probably become a normal process for me. Hate spending money, and really enjoy simplifying the process.