when reusing yeast do you need to up in alochol?

A couple of brew together, and we are trying to figure out if after we rack a beer off a yeast and then add a new wort to the cake: Do you need to go up in alcohol when doing?
We are making ~5% wheat beers. We aren't sure if this going up in alcohol is a general rule, only applies to high alcohol beers, or is just misinformation.

No, you don't have to change the starting gravity when reusing yeast. 99% of brewers brew the exact same beer with their harvested yeast, often for a dozen generations or more.

might want a blow off tube if you making wheat beer on a whole yeast cake.Good luck

Actually, I'd recommend dumping out 2/3 of that yeast cake before re-pitching on it. Yeast generate esters during the growth phase. In some styles, those esters aren't desirable, but you want them in a wheat beer to generate the banana, clove, or bubblegum flavors.

Pitching directly on an entire yeast cake sidesteps the growth phase, leaving little opportunity to produce those esters.

Better even than just guesstimating would be to wash the yeast (instructions here), and prepare a new starter culture. It's very easy to do.

To figure out how much yeast slurry to use, you can go to the pitching rate calculator at Mr Malty and use the calculator to determine how much slurry you need, assuming that your washed yeast is 20% or so non-yeast solids.

I think you'll have better results in a wheat beer this way.

+1 to what jds posted.

GT

A possible source of confusion is, many people like to brew a smaller beer and then pitch a barleywine or some other big beer on the cake. Basically, a 5 gallon starter.