New personal landspeed record

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vasie

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My recent brew schedule has allowed me to brew every two weeks--got some kegs to fill. This has afforded me the chance to pitch new wort on my previous batches yeast cake. On my last batch I pitched a 1.050 wort on a nice thick WLP001 yeast cake and that puppy took off in less that two hours! Damn, that must be a new landspeed record--at least for me. :rockin:

I had to move the fermenter directly into the bathtub filled with cold water to kept the temperature under control. Other than ruining my stick-on temperature strip, I think that all went well, though it was still a bit on the warm side ( around 75 ). I figure that If I leave this wort on the yeast for a month, my yeast army should be able to take down any Diecytl formed during those vigourous 48 hours of churning, burning, fermentation. Anyone else had one take off like this? Everyone figure that a month will be long enough to clean it up a bit?
 
You have to be careful when racking onto a yeast cake from a previous batch, you likely way over pitched and that can cause some issues. Its best to brew a small beer say in the 1.035 to 1.040 range, then rack a really big beer say in the 1.070 range onto it.
 
I've had 30-minute lag times before when pitching onto existing cakes. Damn thing had krausen before I could finish aerating it.

Don't worry too much about overpitching. Dispite Waldo's warning, it's usually no big deal. The worst thing you'll have to deal with is a very vigorous fermentation that heats up the wort to the point where you need to cool it down somehow to keep it in the range. Some people also like to empty out the cake, wash the yeast, then pitch a portion of it back...there's a worry that pitching onto a cake like that skips the initial ramping-up period in the yeast's fermentation process, which supposedly can rob the beer of certain esters that are created by that process. Personally, I've never really noticed any problems other than the heat issue, but that doesn't mean it's not real.
 
This is quoted from http://www.mrmalty.com/pitching.php#E

If you've brewed more than one batch, I'm sure you've noticed that there is a huge pile of yeast in the fermenter at the end. If (and that is a big 'if') you've got excellent sanitation all the way through the process and have provided proper yeast nutrition (including O2), you have a gold mine of healthy yeast ready to reuse. Of course, you don't want to reuse the whole thing. I know a number of people dump a new batch on top of the yeast cake, but you're not going to get the best beer that way. Yeast do need some growth to result in the right kind of ester profile, etc. While too big a pitch is better than too little, it is pretty easy to figure out how much you need and pitch just that.
There are about 4.5 billion yeast cells in 1 milliliter of yeast solids (solids with no excess liquid). According to Fix, in a slurry, only about 25% of the mass is yeast solids. Of course, if there is a lot of trub in there, you have an even lower percentage of yeast solids. The bad thing is that you can't tell how viable that yeast is, unless you have the equipment to properly test and count it. So this is where it gets a little bit like black magic. There are a number of factors that affect the viability of a given pitch of yeast. How old is the yeast? How stressful was their last fermentation? Have they had the proper environment and nutrients for successful reproduction or are they too scarred and tired to go on?
When the yeast is fresh and healthy off an previous batch, viability is maybe around 90%+. It goes down from there fairly quickly without proper storage and it also really depends on the strain of yeast. Unless you're going to get into testing viability, you're going to need to make some educated guesses and keep good notes on the results. This is where being a yeast psychic really helps. Start in a range of 80 to 90% viability and you probably won't be too far off. Use the Pitching Rate Calculator™ to help figure out how much of that yeast you need. If your yeast viability is much lower than 90%, you should probably toss the yeast. If you really want to use it, you might consider pitching it in some starter wort to get the still viable cells active. When they're in solution, decant that active part of the starter into another vessel, hopefully leaving the dead cells behind.
 
I have tried it once and my wort was going in about 30 minutes. I was amazed how fast it started. The bad thing was that I lost around 1/2 gallon in the blowoff. Now I just wash the yeast and add that to the new wort.
 
Yes, over-pitching can occur, and it can be a problem for SOME beers. As Evan says, it is often not a problem -- this would pertain mostly to beers where a clean flavour profile is desired. It would be especially true in hoppy American ales where the hop flavours dominate the beer.

Over-pitching will become a problem, however, for beers where the yeast contribute to the flavour profile. Good examples would be a hefeweizen, Belgians, and fruity English ales. A major component of the flavours in these beers comes from esters produced by the yeast. These flavours largely develop right at the beginning of the fermentation process when the yeast are reproducing (adaptive phase). If you overpitch, the yeast mostly bypass this phase, and the ester/flavour profile suffers.

As one poster suggests, it is best to use the correct amount of yeast for your beer (gravity and yeast/beer style are the important considerations). Jamil's pitching rate calculator is a great tool to help, although you don't need to follow it religiously to make good beer - just get in the ballpark.
 
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