Fermentation / Batch Size

[dustinthompson85]

Might be a silly question, but is there a general rule for what size fermentor should be used for a specific batch size? Should a 5 gal batch always go into a 6.5 gal fermentor? What about a 2.5 gal recipe. What size should it go into? What happens if you put a batch in a fermentor that is way larger than the batch (1 gal batch in 6.5 gal carboy)? What about the reverse (other than blow off)? Just wondering.

 

[dkeller12]

General rule of thumb is to not have large amounts of head space above the fermenting wort/beer. This could lead to oxidation if you have too much space. So a 5 gallon batch should go into a 6.5 gallon fermentor and be fine. A 2.5 gallon batch should be in 3 - 3.5 gallon fermentor. Now, with that being said, I have heard of plenty of people putting 2 gallons in a 5 and 6 gallon fermentor and having no issues. The issue is more important if you rack into a larger than needed secondary. What I do is use the closest to proper size fermentor as possible and not rack to secondary at all unless aging a beer for a long time. In that case, I would make sure I use the proper sized secondary. Good luck.

 

[HaDaL]

Primary fermenter => Remaining 1/5 of It's volume is necessary- 1/4 volume of it remained empty is good - remaining more than 1/3 of It's volume empty is not recommended.
Secondary fermenter => Just a couple of inch empty space may be necessary- filling it up to the near of It's mouth as much as possible is good- remaining more than 1/6 of It's volume empty is not recommended.