Fermenting 9 litres in a FV designed for 20L Litres

[Braufather]

Any issues with doing this? I have a SS brewbucket that i believe is 27 litres volume but want to do a small 9 litres batch instead usual 19l. can i use this anyway? would too much exposure to oxygen be a problem? i can secondary in a corny keg if need be. cheers guys.

 

[terrym]

I sometimes do 12 litres in a nominal 25 litre FV and don't get any issues arising. Oxygen at the beginning of the primary isn't a problem and when the fermentation gets going it will slowly drive out the oxygen in the gas space so it becomes CO2 rich.

 

[Braufather]

thats good to know. going forward i was thinking of buying some 12 litre FV for splitting batches - but it would be cheaper to buy another full size one so may as well do that then.

 

[Hoppyland]

On reading the question, my reaction was that there should be no problem at all - as terrym says the O2 is no problem at first, and you'll generate plenty of CO2 to protect the beer as it ferments. After all, I believe some beer still is commercially produced by open fermentation provided that a top-fermenting yeast is used.
It did make me think, though, about exactly how much CO2 is produced by fermentation, and I came across this:
https://lifefermented.wordpress.com/2014/01/22/how-much-co2-is-produced-from-brewing/

It's a lot more than I thought! I looked it up mainly because I've wondered for some time if I could use the CO2 to purge secondary FVs or storage vessels (I normally keep my beer for a month or so to mature before bottling or kegging it). If a 20l batch of modest-strength beer is going to produce well over 300l of CO2 then I reckon this could be very useful. I presently use a 6 kg welding cylinder of CO2 to purge headspaces, but it seems a shame to throw away so much "free" gas!

 

[Sput]

Interesting, nice link. I sometimes wonder about this when staggering back after getting a lungful of CO2 after opening a long-sealed fermentation freezer.

The question though is how on earth to harvest it (something along the lines of a blow off tube into Star San in a sealed container with a spunding valve that is tightened after the oxygen gets out perhaps??? but any pressure would cause backflow I guess). And then how to store it, especially given that it will need to be under pressure if it's to be a manageable size... Or just leave an open, sanitised Corny keg in a fermentation fridge, let out oxygen now and again and hope for the best?

BTW I also use 7 gal SS Brewtech Brew Buckets for the occasional 10 litre brew and have seen no issues.

 

[Pavros]

I bought a smaller plastic 15l fermenter just for when I split batches or brew the Brewferm kits (which tend to be 8 - 12l).

 

[Pope]

I always brew 10l batches in a 25l FV without it being an issue.

 

[matt76]

I recently brewed a 10L batch in a 25L FV, tasted great when i bottled it. Currently got a small 5L brew in a 15L FV so hopefully it's ok!

 

[braziliain]

Brülosophy did an experiment on this and determined that there was a perceivable difference in the beer. That said, Marshall couldn't tell them apart and it it didn't make bad beer, just different beer.

http://brulosophy.com/2017/03/13/th...pace-during-fermentation-exbeeriment-results/

I quite frequently ferment 10-11L in my 23L bucket and am perfectly happy with the resulting beers.

 

[Hoppyland]

Brülosophy did an experiment on this and determined that there was a perceivable difference in the beer. That said, Marshall couldn't tell them apart and it it didn't make bad beer, just different beer.

Thanks for the link. Very interesting. Of course these Brulosophy trials are not an exposure of irrefutable universal truths! But, they aren't supposed to be. However, they are conducted with a reasonable amount of rigour and certainly deserve a lot of respect. So, I was very surprised that there seemed to be a statistically significant difference between the beers (or at least the tasters perception of them). As you say, though, it seems odd that the author said " I simply could not tell these beers apart, they tasted exactly the same to me, which surprised me given the results. As for the beer, it was alright."
I do wonder, though, if the headspace was in fact the critical variable between the two "otherwise identical" brews. After all, one was 2.5gals and the other 5.5gals. Since they were both in identical carboys, this means that the depth of beer in one was over twice that in the other. Now, it's not obvious precisely how old the beers were on serving, but we have: "Activity was dwindling by 5 days in, so I bumped the temperature up to 72°F/22°C" and then "Following a brief period of burst carbonation, I reduced the CO2 to serving pressure and let the beers condition a few more days before serving them to tasters". This suggests to me that the beer, although it had been fined and cold-crashed, was still very young indeed. It seems to me to be plausible that the perceived difference in the beers might not be due to the headspace, but to the fact that there was more than double the depth of a "young" beer in one container, and that this could have a pronounced effect upon the maturation of the beer. Pure conjecture of course.......