Good point and you should run half the cake out the fermenter tap** before brewing on top of it. Otherwise there is too much yeast and it's party time for the yeast. Aim for maybe 1 cup or 250 mls yeast slurry left. That is plenty. Using a whole yeast cake has negative benefits and one is a huge mess.If you have to do it its a good way to save heaps of time, but that is usually taken up cleaning out the fridge after the krausen explodes out of the top of the fermenter and coats the fridge and floor lol
So you're brewing the same brew twice in a row? That's a pretty good way to get a comparison. You must love your house beer though!! What is it?I have never noticed off flavours, a very slight difference sometimes better sometimes not. I brew 42lts and the beer that goes ontop is the same as the one that came out. Also when I get to do a side by side the first one has been in the keg for 7-10 days longer so that would affect it to.