Pitching onto yeast cake

[sar_dog_1]

Hello fellow brewers! Quick but probably silly questions.
First, I wanted to try pitching a new wort batch on an old yeast cake (same day) and I was wondering if there was anything special I needed to do? I am guessing just rack off fermented wort to bottling bucket, sanitize mist over the top , and rack freshly cooled wort onto it. Gently stir, cover, airlock and wait. Is that all there is to it or am I missing something?

Secondly, if that is correct, does the yeast cake become that much thicker during racking the second batch? Anything to worry about there?

Thanks in advance and brew on!!

 

[LLBeanJ]

Sure, you could do that. It would be a severe overpitch, but there are worse things you could do. As far as stirring, you don't have to, and if you do, you don't have to be gentle about it. In fact, you want to be as aggressive as possible.

The cake will thicken some due to trub in the wort, but it won't be that much. Due to the overpitch, there will be little to no new yeast created.

Rather than pitch on the whole cake, you might want to consider just using enough slurry to get the job done with a healthy fermentation. Usually, all you would need is about 1/2 to 3/4 cup of slurry. If I were you, I'd rack my existing beer off the cake, pull out the necessary slurry into a sanitized jar, clean the bucket, add your fresh wort, oxygenate it as well as possible, then pitch the slurry.

What is the expected OG and volume of the new batch?

 

[WoodlandBrew]

Yes, you'll want to pour off about 2/3 of the yeast. Then add the fresh wort and aerate as usual.

The number of yeast cells produced is directly proportional to the amount of extract available and is (mostly) independent of initial gravity and cell count. Roughly 1 billion cells are grown for every gram of extract. This is known as the Balling Observation.

See here for details:
http://www.woodlandbrew.com/2013/03/yeast-propogation-with-aerobic.html

 

[sar_dog_1]

Not sure thr og of new batch. Prolly low 50s. First batch will be 1.037.

Woodland brew is that 1/3 of yeast and trub? Or do I have to wash it first and take 1/3 of yeast and make a new starter? I was hoping to bottle and then brew a new batch to pitch on used yeast cake. If you mean just remove 2/3 of slurry and then pitch new wort on top of that then great! And thanks!

 

[solbes]

If you pitch directly onto a whole cake, be prepared for a fast (or possibly violent) fermentation. Watch carefully to see if you need a blowoff because its going to be all done in 2-3 days with that gravity. Would not recommend this if you use certain belgian yeast strains, as they are hard to constrain even with fermcap-S.

The best yeast is on top (not at the bottom, which is mostly trub). When I do this, I have 2 buckets. One that is clean and sanitized ready to go for the new brew. I take a sanitized 1 cup glassware and scoop 1-2 cups of yeast/trub from the top and into the wort in the 2nd bucket. Shake it up and airlock it, done!

For my up and coming Dopple Bock, I have four 1 quart sanitized jars that have separated into about 2 quarts worth of yeast/trub harvested from my Vienna. Dopple's need a ton of yeast if you are fermenting on the low end of the yeast. It will lager all winter long

 

[LLBeanJ]

Not sure thr og of new batch. Prolly low 50s. First batch will be 1.037.

Woodland brew is that 1/3 of yeast and trub? Or do I have to wash it first and take 1/3 of yeast and make a new starter? I was hoping to bottle and then brew a new batch to pitch on used yeast cake. If you mean just remove 2/3 of slurry and then pitch new wort on top of that then great! And thanks!

For an OG in the low 1.05x range, 1/2 cup (~100ml) of unwashed slurry is all you'll need for a healthy fermentation. Even 1/3 of the total trub would be a major overpitch, though I'm sure it wouldn't hurt anything if you used that much.

 

[stpug]

My process rarely includes pitching new wort on an entire yeastcake. There are extenuating/special circumstances where I would do this, but not when brewing equal sized batches of normal gravities. 1/3 of the yeast cake includes the trub - no need to rinse/wash first.

Also, no need to spray sanitizer on your yeastcake before pitching your new wort on it.

Lastly, THE BIG CAVEAT, if you've never pitched a beer on a yeast cake and the idea sparks your interest then by all means, do it! You'll never have the experience or first-hand knowledge of how beer is made on an entire yeast cake if you don't try it yourself. I've done it twice; both beers came out good; I got to experience the process; and I don't need to do it anymore. Keep fermentation temperatures in check and be prepared with a blow-off setup and you'll be fine.

Cheers!

 

[andrewmaixner]

If you pitch directly onto a whole cake, be prepared for a fast (or possibly violent) fermentation. Watch carefully to see if you need a blowoff because its going to be all done in 2-3 days with that gravity. Would not recommend this if you use certain belgian yeast strains, as they are hard to constrain even with fermcap-S.

This. I dumped a 1.080SG onto a us-05 yeast cake, and the krausen ended up clogging the 3-piece-airlock base which was attached to the blowoff tube -- note that the airlock base is a pretty small hole, so it somewhat nullified the point of the 1-inch blowoff tube. This resulted in a krausensplosion and an hour+ of cleaning the utility room. I still occasionally find clumps of dried yeast and hop matter in random places in that room.

 

[LLBeanJ]

Lastly, THE BIG CAVEAT, if you've never pitched a beer on a yeast cake and the idea sparks your interest then by all means, do it! You'll never have the experience or first-hand knowledge of how beer is made on an entire yeast cake if you don't try it yourself. I've done it twice; both beers came out good; I got to experience the process; and I don't need to do it anymore. Keep fermentation temperatures in check and be prepared with a blow-off setup and you'll be fine.

+1

I've done it myself when I was young and naïve. It worked out fine the 2 or 3 times I did it. At least, as far as I could tell, anyway. But as I gained more experience and knowledge concerning brewing, I realized that it's rarely ever necessary to use the entire cake. I often repitch slurry, but only as much as is needed and no more, which is usually <1/10th of the total cake.

 

[WoodlandBrew]

I would do it the way stpug mentioned. The 1/3 of the cake estimate is worst case not knowing the gravities of the beers and how you brew, but given your numbers 1/10th is probably closer to a typical pitch. (calculations below)

For a 5 gallon batch of 1.037 batch you probably pitched about 140 billion cells. Typical cell growth is 1 billion per gram of sugar, so based on the starting gravity about 2.1 trillion cells would have grown for a total population of about 2.2 trillion cells. ABV would be about 3.5% which would cause some cell death over time. Assuming it was conditioning for 2 weeks it's probably at about 90%. (see: http://www.woodlandbrew.com/2013/01/abv-effects-on-yeast.html ) That's 2 trillion viable cells remaining.

For your next beer assuming your OG comes in at 1.050 you'll want about 200 billion cells. That's only a tenth of the cake. If you are brewing all grain and pouring everything from the boil kettle into the fermenter cell is normally about 1 billion per ml, but if you are brewing extract, or making an effort to separate the protein before adding the wort to the fermenter you are probably more like 2-4 billion cells per milliliter.

&#8230; So 200 billion cells is between 50-200 ml.

 

[solbes]

Calculations above are all good. I try to remember that what I pitch is not entirely yeast slurry though. I generally pitch the watery stuff on top that is at most 50% solids. Add in allowances for trub included in the yeast and I'm guessing no more than 1/3 of a 1 cup pitch is actually yeast, viable or not. So I pitch 1-2 cups for most beers under 1.060. Scale it up from there for ales. And use a whole ton for lagers.

 

[solbes]

Also should mention that I did once try a pitch onto a whole cake. It was my second Belgian, a Tripel (WY3787). Boom went the bucket lid (while I was away from home). What a mess The flavors ended up being just fine, I got the esters and phenols I expected out of it.

 

[WoodlandBrew]

Good point about the percentage of solid material. My numbers are for completely settled slurry. 50% solids is a reasonable assumption if you don't have time to crash it.

 

[william_shakes_beer]

Keep in mind that hops and wort traces from the first batch will carry through the cake to the second batch. Might make recreating difficult if you really like the resuilt. In general going between 2 batches of the same recipie or from a light to a darker beer will be less noticable.

 

[LLBeanJ]

Keep in mind that hops and wort traces from the first batch will carry through the cake to the second batch. Might make recreating difficult if you really like the resuilt. In general going between 2 batches of the same recipie or from a light to a darker beer will be less noticable.

Good point. All the more reason not to overpitch when pitching slurry.