Wine fermentation containers and headspace

Question

I'm starting my first attempt at wine-making, so please pardon the noob question....

I have two 6 gallon buckets with airlocks. But the "Winexpert" kit I've got recommends 8 gal for primary, and 6 for secondary. Actually, the box says "no less than" 8, while the enclosed instructions say "up to 8", and say to top off the bentonite+juice to 6 gal with water at the start.

So I am a little confused over managing the volumes.

1: Why the extra 2 gallons of space? Is there that much expansion during primary fermentation? Or is this just to allow for foaming without making a mess? Can I use my 6 gallon bucket?

2: Should air be able to get in during the primary fermentation? I gather that some people ferment with just a cloth or loose plastic cover, while others use a real lid and airlock. I saw primary fermentation of wine, which seems to suggest that opening to stir adds enough oxygen. Am I understanding this right?

3: When siphoning to the secondary, I'm going to have well under 6 gallons because of the lees left behind, right? But I've found conflicting advice on whether/how to top off the secondary container. Is the main reason to do that, excluding Oxygen? What else do I need to know about for this? I did see Fermenter Headspace; Suitable (and cheap!) Containers for Split Batches.

Can I use a 5 gallon carboy for a 3 gallon batch of wine? suggests that extra head space in the secondary isn't very important?

Thanks!

Answer 1

Let me answer your questions

1. You will need that 2 gallons of head space for foaming. Don't use a six gallon bucket.
2. Air is less of a concern during primary because of the volumes of CO2 produced but once the active fermentation has stopped, you need to be sealed in a carboy that is topped just a couple of inches from the bung.
3. You want as little headspace as possible. Just and inch or two below the stopper in the carboy. If you can't fill a six gallon carboy, then get a five gallon one. Do not use a five gallon carboy for a 3 gallon batch for long term storage.