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Home Brew Forums > Home Brewing Beer > All Grain & Partial Mash Brewing > Pitching on Yeast Cake - Approx. how much will this effect my OG reading?
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Old 03-29-2008, 07:16 PM   #1
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Default Pitching on Yeast Cake - Approx. how much will this effect my OG reading?

So i'm pitching a Rye Pale ale on top of a IPA batch that used US-05 yeast. Considering i feel like i should have a pretty clean yeast cake with very little hop debris/cold break, how much do you think it would effect my OG reading?

I am only doing PM batches so i do use top off water thats why i cant just take a reading before going into my primary.

Would an +.01 be out of line? more or less?

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Old 03-29-2008, 07:23 PM   #2
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I think you can drain your wort into the fermenter, add the top off water, mix well, and get an accurate gravity reading. The yeast cake shouldn't affect it to much at all.

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Old 08-04-2012, 11:38 PM   #3
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I know this is an old thread, but I just did a partial boil extract batch and poured it right onto part of a yeast cake that I had just transferred another batch off of. So, I ended up with this same question.

Does anybody have a different opinion than was previously given in this thread, or was RichBrewer on the money?

Any thoughts would be great. I'm not worried about my batch, but when the predicted OG was 1.060 and my measurement came out at 1.090, I knew something wasn't quite right. I also probably fell prey to the mistake of not thoroughly mixing in the top-off water.

Like I said, it was an extract batch, so I'll just make my ABV calculations based on the predicted 1.060 OG and not stress too much about the disparity in my reading. It just seemed like an interesting aspect of the process and piqued my curiosity.

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Old 08-05-2012, 03:28 AM   #4
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Quote:
Originally Posted by signpost View Post
I know this is an old thread, but I just did a partial boil extract batch and poured it right onto part of a yeast cake that I had just transferred another batch off of. So, I ended up with this same question.

Does anybody have a different opinion than was previously given in this thread, or was RichBrewer on the money?

Any thoughts would be great. I'm not worried about my batch, but when the predicted OG was 1.060 and my measurement came out at 1.090, I knew something wasn't quite right. I also probably fell prey to the mistake of not thoroughly mixing in the top-off water.

Like I said, it was an extract batch, so I'll just make my ABV calculations based on the predicted 1.060 OG and not stress too much about the disparity in my reading. It just seemed like an interesting aspect of the process and piqued my curiosity.
If you used all the extract and had exactly 5 gallons of water, your gravity CAN'T be off. It is almost certain that it was not mixed well enough to get accurate gravity reading. Any time you do an extract beer, you can basically be 100% certain that your gravity is correct so long as you use all the extract and have a 5 gallon batch.
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Old 08-05-2012, 04:17 PM   #5
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Quote:
Originally Posted by Braufessor View Post
If you used all the extract and had exactly 5 gallons of water, your gravity CAN'T be off. It is almost certain that it was not mixed well enough to get accurate gravity reading. Any time you do an extract beer, you can basically be 100% certain that your gravity is correct so long as you use all the extract and have a 5 gallon batch.
So, no thoughts on my actual question?
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Old 08-05-2012, 06:03 PM   #6
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So, no thoughts on my actual question?
well in round numbers if we assume the yeast cake to be finished beer gravity and 10% of the total batch volume...your og will be lowered by roughly 10% times the attenuation rate of the yeast...say 80%.

Sooo, 80% of 10% would be roughly an 8% lowering of your new batch OG...of course actual mileage may vary or in other words RDWHAHB and don't get tangled in the numbers...it's only beer.
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Old 08-05-2012, 08:25 PM   #7
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Pitching onto a yeast cake doesn't change the original gravity at all. The specific gravity is a measurement of dissolved solids in the wort. The small amountof beer in the yeast cake when blended with the new wort may drop the gravity slightly, but I would say less than one point.

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Old 08-05-2012, 08:39 PM   #8
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FYI - in the Yeast book they advise against pitching on a previously used yeast cake, saying it wont be as good.
They say that is a good example of over pitching yeast.

You can still get ok beer, but they say it will be better tasting if you dont pitch on a yeast cake.

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Old 08-05-2012, 09:54 PM   #9
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Originally Posted by Mikethepoolguy View Post
Pitching onto a yeast cake doesn't change the original gravity at all. The specific gravity is a measurement of dissolved solids in the wort. The small amountof beer in the yeast cake when blended with the new wort may drop the gravity slightly, but I would say less than one point.
Yes. Items in suspension, in this case yeast cells, do not affect the gravity. Items in solution, in the case of brewing being sugars, are what affects the gravity.
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Old 08-05-2012, 10:00 PM   #10
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Quote:
Originally Posted by ArcLight View Post
FYI - in the Yeast book they advise against pitching on a previously used yeast cake, saying it wont be as good.
They say that is a good example of over pitching yeast.

You can still get ok beer, but they say it will be better tasting if you dont pitch on a yeast cake.

While pitching on yeast slurry may be technically overpitching, it is very unliikely to cause any negative effects. While I have seen this warning a number of times I have yet to hear of a case with any specific problems caused by doing so nor have I ever encountered a problem in the many times I have done it myself.
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