How much space to leave in primary fermenter?

[ThePrisoner]

How much space should be left when doing the primary fermentation in:
- a 15 gallon basket type demi john?
- a 1 gallon jar?

 

[Lodestone]

Head space isn't as important in primary as it is in secondary and tertiary. I personally plan primary batches on what I know I will have available for secondary. If I know I am only going to have a 3 gallon and and 1 gallon for secondary the primary will only be 4.5 gallon in a 5 gallon carboy. Most ciders don't have large amount of krausen unless you have fruit of some sort in primary (not recommended fruit should be added in secondary to preserve flavor). I find a half gallon space to be more than enough to prevent any blow out. But if you are truly worried about it you can use a blowout tube instead of an airlock.

 

[Maylar]

I can't speak about big fermenters, but here is an example of two 1 gallon jugs a day into primary. I've learned to leave enough space for the krausen so I don't get overflow.

 

[ThePrisoner]

Can you sterilise and reuse wine bottle caps for a still cider?

 

[m00ps]

the OG and yeast selection also depends on amount fo headspace needed. For me, roughly 20% headspace is usually pretty good for an OG below 1.060. Cooler fermentation will make it less vigorous. The shape of the vessel plays a role too. Anything which taper in at the top will need more room it seems (not just volume wise). I think this is because there isnt as much surface area for the krausen at the top

use fermcap if you are worried about headspce

 

[Frognostic]

I haven't used a gallon jug for primary fermentation in a while but my memory of it is foam going through the airlock.

I use plastic buckets covered with sanitized tea-towels secured in place with elastic bands fill up it just over half way.

I rack it into the glass jug when the fermentation has died down enough to not send foam through the airlock and fill it up as much as possible without the liquid actually touching the bung.