Stopping (slowing) Fermentation early

[Benjybo]

I'm a Engineer by training who has now found myself running a long standing (20 yr+) brewery in the UK. I have no background in brewing, but have strong background in everything else it takes to run a brewery. I've therefore set out to learn everything I can about about the brewing side.

There's one thing that I am confused about however, and this is our (and many other breweries around us) policy of stopping fermentations by skimming (open tops) and applying cooling before a beer has fermented out (typically somewhere between 1012 and 1010... 3-4 points above where we expect it to finish.. ( however no brewers I have spoken to seem to have done a forced attenuation to check this point)).

Now I understand this policy for cask beers, where we are looking for further fermentation to take place in cask, but this policy doesn't generally change when we are brewing beers for bottle or keg. In fact many times we split a brew 50:50 bottle and cask.

All the reading I have done ( brewing elements yeast for example) talks about fermenting out, and letting the yeast 'clean up' the beer. My feelings are that by continually stopping (slowing) fermentations at 1010 (maybe 1012 if they are fast) we aren't letting the yeast do this and are also leaving a relatively unstable beer in bottle with high levels of fermentables (we aren't bottle conditioning bit do generally sterile filter)

I have spoken to our brewing consultant (who is pretty old school) and others and no one else seems to see a problem with stopping early ... Although it seems to be against all the reading I have been doing. In fact I can't find anything at all about stopping fermentations early.. Except in relation to cask. Our own head brewer learnt on the job so does it this way as it is the way we always have done. I'm now finding myself in disagreement with our brewing consultant who is more than aware that I have no brewing background.. So doesn't really rate anything I have to say in the subject.

The general argument against fermenting out is that it will effect the mouth feel etc, but again should we be relying on fermentable to provide this? Or adjusting receipe / mash temps etc to increase non fermentable sugars? My reading suggests the latter.

Anyway I am just after some thoughts as to whether I'm missing something here? Or are we (and others around us) just blindly brewing in the way they always have.. Without thinking to adjust things for bottle or keg.. And letting the beer finish fermenting properly.

Thanks for your help!

[mpilchuk]

Benjybo,
Interesting. We don't generally stop fermentation as a rule, at least in my history as a home brewer (21yrs) and a pro brewer (1yr 5 months). I let my beer ferment out and allow the yeast to clean up the beer before I keg it. We don't bottle. In home brewing, you take a gravity reading and don't bottle until there is no further gravity drop. if you bottle before that, you can create bottles that explode when the beer is allowed to further ferment. Most of the home brewers that I know (and myself at my brewery) are continually making different beers (and we don't do casks the way they are supposed to be done, we add sugar). In the UK, from my 3 months there in the brewing world, they seem to make the same beers over and over and I would not see the need for an attenuation test in that case. I was at Gadds brewery and happened to see one of the brewers doing an attenuation test. I had been in the UK 5 weeks in training and had not run into this. It wasn't even mentioned in my training. I spent a lot of time trying to figure out how real ale re-fermented in the cask in the UK. I know when I had done it as a home brewer, I added sugar. I didn't see any sugar being added in the UK.

I'm gonna have to get myself making a real ale by stopping the fermentation. I usually fill a few pins off of a beer batch that I'm going to keg so add sugar, but I'm gonna start doing smaller batches just for cask. I only have 4 pins and a few firkins so it can't be all that big a batch, almost home brew really.

If you don't bottle condition, how do you get carbonation into the beer? Also when you say skimming, are you just referring to taking yeast off the top of the FV?

I really enjoyed most of the real ale I had when I was there, but I have to say, you guys aren't so good at bottling beer. I didn't find the bottled beer as good as the stuff on hand pull.

[jwalts]

Stopping the fermentation early sounds like a recipe for diacetyl and acetaldehyde to me, but sterile filtration should prevent bottle bombs as long as the downstream processes don't introduce yeast or bacteria (e.g. from equipment that touches both ambient air and beer during bottling). UK brewing practices are somewhat of a black box to me, so take my advice with a grain of salt, but my first impression is that you're exactly right: stopping the fermentation early is a procedure for cask production - where the yeast will have another chance to consume residuals sugar and reduce undesirable compounds - and shouldn't be practiced for production of packages that don't utilize refermentation.

Joe

[Alphaacid]

Large breweries will stop fermentation early to keep on schedule, hence all the acetaldehyde in most lagers found around the world.

Let the yeast do it's thing, then let it sit. Pick up a copy of Yeast, I can't remember who wrote it

[ghobbs]

I totally agree with jwalts on this.

When we're casking our beer, we crash the beer early, as you do, saving those residual sugars for the second fermentation in cask. The warm conditioning period we allow it after it's racked allows the yeast to go to work on the sugars increasing the ABV and the carbonation, but also mopping up any undesirable fermentation by-products.

For our carbonated products (kegs, bottles and cans), we ensure we're fully fermented out (we don't filter) and run diacetyl tests before crashing the beer. I would be concerned with off-flavours coming through from not allowing the yeast to finish doing its job. You may find you need to tweak the mashing schedule to compensate for a drier product, but with this approach it should be more in-line with your finished cask beer disregarding the difference in carb levels and serving temp.

I'd be interested to know whether your bottle/keg beers taste sweeter than the cask counterparts? And presumably the conditioned cask is also higher in ABV? If you want to know what the terminal gravity is without running a dedicated forced fermentation or attenuation limit test, you could always pull a gravity sample from a finished and conditioned cask to give you an idea of whereabouts you're finishing up - we put a cask aside from every batch and run a chem and sensory analysis on it after a week or two (depending on ambient temp) before release to sales.

[wailingguitar]

Not letting beer reach terminal gravity is a disaster waiting to happen. If you stall fermentation early, unless you pasteurize or sterile filter your beer there will be living yeast hanging out. If you then force carb and bottle or can the product, the day it gets warm that yeast is going to get happy with the remaining sugars. Congratulations! Your beer is now over carbonated!

Even for cask products I would argue that it is best to let the beer reach terminal gravity before filling casks. The reason is that the yeast has time, as you noted, to clean up after itself for one, and for two you then have a precise way of determining how much fermentable sugar (in the form of corn sugar or what have you) that goes into the cask for a more consistent degree of carbonation.