I'm making a 2 gallon Brown ale but my dry yeast pack is for 5 gal. Do I just pitch it all or half or proportionately?
Theoretically it is over pitching, which may lead to reduced yeast character, but you probably won't notice a difference. My concern with pitching half a pack is being able to keep the other half from being contaminated. (Assuming you are saving the other half)
I make 2.5 gallon batches regularly. If it's a high gravity beer, I pitch the whole pack. If it's lower gravity (1.055 or below), I pitch half. I just squeeze all of the air out of the package and tape it up tight. I refrigerate the rest and try to use it within two months. I have never had any issues using the leftover yeast.