OK to pitch new wort onto sediment in primary?

I have a beer ready to come out of primary and I am going to brew a new beer that will use the same yeast strain. Is there any reason I can't just rack the finished beer to secondary and pour the new wort into the primary? The primary is about 10 days old so I don't figure there is a huge risk of autolysis, right?

Many people do this but there are a couple things to keep in mind. There is a lot of dead yeast cell and hop debris in the current yeast cake. Is the second beer you want to brew similar to the first? Will the remaining hop debris cause your new batch different flavors than you want? Are the gravities similar as you may stress out the yeast with a big difference? Did the first beer turn out as you had hoped with a healthy fermentation and no off flavors?

I do practice the re-use of yeast but I don't just re-pitch onto the cake for all the reasons above. I prefer to harvest, wash and save. If I ever get a beer that doesn't turn out like I expect it to I just dump the yeast and start fresh.

Do it and tell us how it turns out! Note that when you rack onto an old yeast cake, you are starting your next beer with a lot of yeast. Esters and aromatics seem to be correlated with yeast reproduction. Since you have more yeast to begin with (several times more than you probably originally pitched with your smack pack / tube / starter), there will be less ester and aromatics production. Those are characteristics of some beers, but not others. If you have a clean, neutral yeast, or are going for that in your beer, it should work well.

I did this recently with two batches of hefeweizen in a row. (Wyeast Weihenstephaner 3068?) The ester/phenol production was fine. The second beer came out nice and cloudy with plenty of banana and clove but the trouble was really all the extra trub. It took up more than a 1/2 gallon out of 3.5 gallons! The bottles had lots of trub in them too. The fermentation took off like a rocket though and I don't know if any less than 2.5 gallons of headspace would do either. Next time I'll wash the yeast for more repeatable results.

Good to know the flavors came through fine. I've never racked onto a yeast cake, but from what I've read about ester production, hefeweizen would certainly be a style I'd be cautious about brewing this way. Sounds like maybe it isn't that much of a concern after all.

Make sure you have blow off on airlock. I do this all the time and it works as long as beer s are similar in style. I keep a ipa going on the same yeast. After the second time I dump some out and pitch again. After three times I start over.
I have spoke to breweries about this and they go up to 10 times with the same yeast. But they also have the exact same recipe.
Do a search on this topic and there are plenty of good pages of reading.

Blow off is key though. It will be very active

Pitching onto an entire cake will undoubtedly be a massive over pitch and may not give you the desired effect. As another poster stated, ester and phenol production happens during the reproductive phase, which won't happen with an over pitch like that. I'd suggest washing the cake and using something like MrMalty to gauge how much of that washed slurry you should pitch.
As far as autolysis.... not likely in ten days, or ten weeks.... ten months, maybe. The myths of autolysis happening in the typical homebrew setup have long since been disproven.

I've taken your (collective) advice and done a yeast wash. I took about half the trub/cake and washed it and collected about 8 oz of milky-colored yeasty liquid. I'm now curious how much of that to actually pitch?

sideshow_ben said:

I've taken your (collective) advice and done a yeast wash. I took about half the trub/cake and washed it and collected about 8 oz of milky-colored yeasty liquid. I'm now curious how much of that to actually pitch?

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As a rough guide, the yeast in the fermenter will be about 6 times the recommended amount to pitch for a beer of the same gravity.

I will generally use about a quarter of a cake (I assume some yeast has died) when I repitch into a similar gravity beer.

Check out this site for some good info on how much slurry to pitch. Also, many times I will take ~150 ml of yeast solids after being washed and pitch that into a brewing starter the same way I'd pitch a smack pack. Seems to work well, but there's def more accurate ways to ensure you're pitching enough slurry.

Well I tossed in one cup yesterday at noon and 24 hrs later I have vigorous fermentation.