reader question: British ale fermentation techniques

Reader and Berliner Weisse brewer Scott hit me with this recently, and it was too chewy to not repost here:

So I recently came across this thread on Homebrew Talk (

Anyway, my initial question has less to do with the subject of the thread (ferm temps) but more to do with something one of the responders noted.   His premise was that for lack of a better term “head pressure” during fermentation didn’t allow full expression by some of these British yeasts.  He advocated an “open” or “semi-open” fermentation.  I was wondering what your thoughts on this subject matter?  Would a closed environment have an off affect than an open free release of gases environment?

The short answer is … okay, it’s not that short, and it does have a few buts.

The not-short answer

Open or semi-open fermentation systems with English ale strains (or any yeast, for that matter) will produce a different result than a closed, airlocked system – I don’t think it’s fair to say the effects of closed system are totally negative for English strains (more on that later).

The ready access to atmospheric oxygen that an open, non-pressurized fermentation affords the yeast cells promotes growth, which in turn encourages synthesis of (particularly ethyl acetate and isoamyl acetate). All other things being equal, a closed system will produce a lower, less complex ester profile.

Open fermentation is a great trick to have in the playbook for tweaking the profile, not only of English ale styles, but just about anything – Weissbiers and Belgians, natch, but it’s also still practiced by some lager brewers. Anchor Steam and Sierra Nevada Bigfoot are both still done in open tanks.

Now, leaning heavily on Brewing Yeast & Fermentation by Messrs. Boulton & Quain, I arrive at a Sir-Mix-A-Lot-video level of buts:

First But

A major environmental factor that also affects yeast behavior is fermenter geometry: it’s important to remember that when discussing these open systems, the fermentation is conducted in broad, shallow tanks versus the tall, narrow and deep modern cylindroconicals. (I’ll plug JD’s excellent experiment again here, which demonstrates the effects of geometry on flavor in a Weissbier fermentation).

In a tall, narrow tank, the fermentation tends to be more turbulent, which (again, all other things being equal) creates a faster rate of fermentation. In a broad, shallow tank, the fermentation rate tends to be slower, leading to less scrubbing of volatile aromatics by escaping CO2; it also tends to promote lower attenuation (the tradeoff is that it’s much easier to keep highly-flocculent strains in suspension and at their work in a shallow vessel than it is in a tall one).

In an open-system with a  top-cropping strain (like many English ale yeasts are), the traditional method is to skim yeast from the surface; because – as Boulton & Quain write – isohumulones selectively bind to cell walls, this practice reduces bitterness levels in the finished beer.

All of that sets the stage for some fairly significant differences in sensory profile; some of the variance is probably strain-dependent (3068, for example: highly manipulatable), but overall I’m not sure the changes would be that dramatic in a closed vs. open system on a homebrew scale without also adjusting the fermentor depth … a bucket or carboy is taller than it is wide, which, I would guess, would mitigate the effects somewhat.

Second But

Speaking of depth – the headspace pressure is one of the factors attributed to ester suppression in a closed system; however, pressure is exerted on cells not just by gas in the headspace of the fermenter (which is escaping through an airlock anyway …) but by the density of the wort as well as the height of the fermentor. So depth again – shallower fermentation vessels mean less osmotic pressure on the cells. The pressure being gradually burped through the airlock during active fermentation in a closed system shouldn’t be enough to reach the levels required to actively suppress the formation of esters and other volatiles.

Third But

Boulton & Quain, everybody:

Regardless of the pros and cons of traditional versus deep fermenters, the industry has made a decision, and in the vast majority of commercial breweries beer is fermented in large-volume vessels. Thus it is reported that only 5% of total beer production is now produced by top fermentation.


… the Whitbread Brewery in the United Kingdom installed cylindroconical fermenters with capacities of 1200 hl and wort depths of 6 m. Using these vessels, ales were produced that were considered analytical and organoleptic matches for similar beer fermented in traditional shallow open vessels.

Being a good Luddite, I will go through the motions of shaking my fist and grumbling that things aren’t as good as they used to be (which reminds me, I need to order the 20th anniversary edition of Bleach … damn kids and their Skrillex). But it does raise the point that odds are good that a lot of the classic English ales we’re drinking today aren’t fermented the way they used to, and reminds us that yeast is a living organism and will adapt (or can be made to adapt) to new conditions.


Man, I need a beer and an experiment. I propose that, first, we all get a beer (or at least a coffee and an IOU to yourself for a beer); then anybody that cares to join me in conducting a split batch of some sort with an English ale strain – closed vs. open/non-pressurized, or perhaps tall and narrow vessel vs. broad and shallow. This is opportune, as I have a pack of 1469 that needs to get used. I’ll detail that brew session and results in a future post, everybody can share their results in the comments, and we can perhaps build a little compendium of flavor effects on various British strains.


26 thoughts on “reader question: British ale fermentation techniques

  1. The place I work at (Brauhaus Faust) also uses open fermentation for all of its beers. I would add another variable to the mix: open fermenters allow brewers to physically remove unwanted substances (hop resins/tannins/leftover cold break) from the krausen layer. I think that all of our lagers share an uncommon ester profile that is most likely derived from our shallow primary fermenters. It definitely gives us a “house flavor” that differentiates us from the modern day, standard German lager.

    Here’s a link to an album with a couple of shots of our open lager fermentation:

    • Awesome, thanks for the comment. A couple of the sources I consulted also cited a reduction in bitterness due to isohumulone binding to yeast cell walls, which would then get removed along with skimmed yeast in an open fermentor … so that further changes the character of the finished beer.

  2. Footnote: Osmotic pressure is governed by the molality (i.e. moles solute/kg of solvent), the van’t Hoff factor (i.e. the nature of the solute) and the temperature. The hydrostatic pressure, however, experienced by the yeast depends on the pressure in the headspace, the density of the liquid and the depth of the yeast below the surface of the liquid. Nerd up.

  3. Well you know I’m in. I am planning to get identical fermentation chambers (read: buckets) and lid one and not the other. I hope to brew this in the next couple weeks, will probably use 1968.

  4. Dang – day late and a dollar short. Yesterday I just brewed my last in a series of brews using WLP037 (Yorkshire Square). Being the Yorkshire square strain, I had to give the open-fermentation thing a try. They were all fermented in buckets with a paint-strainer bag over the top to keep out any unwanted macroscopic guests. Once the krausen fell, I lidded them up as normal. Maybe the next time I need to fill up my English Ale pipeline I’ll brew some split batches between a BB and an open bucket.

    I’m not sure I buy the whole “access to atmospheric oxygen” thing, since an active fermentation is pretty much going to be blanketed with CO2, even in a shallow vessel with little-to-no headspace. My money is on pressure, since pressurized fermentation is purported to minimize ester production.

  5. Thanks for the 15 minutes of fame again by linking to my geometry experiment. We’ll have to do some fishing in repayment – email me.

    So experiment – English yeast
    Just when I thought I was out, they suck me back in…

    What kind of headspace do you want to test?
    I was thinking 1 6 gallon batch spilt two ways.
    2 6 gallon carboy – 1 with foil, one with airlock.
    2 5 gallon carboy – 1 with foil, one with airlock.
    1 6 gallon carboy, 1 5 gallon stainless steel rectangle fermentor filled with 3 gallons.

    Whitbread 1099 yeast
    I’ll do a Whitbread X from 1917 recipe via.

    Served on beer engine, co2, or bottled.

    You let me know fermenter and serving preference (beer engine).

  6. I made this experience: I brewed an ESB, a Weizen and a Pils and fermented side by side, one semi-open and another colsed. The only beer I got a significant difference was the pils: a hint of ester an no sulphur aroma in the open fermented beer, and a hint of sulphur and no ester in the closed fermentation.

    • Interesting results. That makes me think that WY2007 has potential for a really nice IPL fermented open and on the warm end of it’s temperature range. I picture that Bud-like apple ester would be really nice with Nelson Sauvin and some fruitier hops like Citra and Meridian.

      • Agreed! I never used Meridian, but I made a nice IPL with NS and Citra. In both beers (the Pils and IPL) I used the strain 34/70 (WY2206 & WLP830).

  7. Brewing this either Sunday or Monday.
    10 gallon batch split between ale pails. Closed vs open.

    Golden Promise 98%
    Simpsons Medium Crystal 2%
    1.25 oz Northdown (45 min)
    1.00 oz Northdown (20 min)
    0.50 oz Northdown (5min)
    Wyeast 1968

  8. We’re really talking about “open fermentation” and comparing buckets and carboys to 18′ tall conical fermenters? If you think there’s a difference between lid on and lid off in a 2′ tall plastic bucket, you’re only deluding yourself. For all practical purposes, all homebrew fermentations outside of a pressurized and sealed conical are open fermentations. Any changes in yeast character are better explained by chance than anything else.

    • Thanks for the comment! The purpose isn’t to compare buckets and carboys to commercial-size cylindroconicals (although the above quotes from Boulton & Quain are comparing commercial-size cylindroconicals to commercial-size Yorkshire squares and other traditional open systems) – I agree that the fermentation dynamics on such different scales would be quite different.

      I’d also concede that, at least for some strains or families of brewing yeast, as a determining factor in flavor and aroma, fermenter pressure and depth take more of a backseat to factors like temperature, O2 levels, and pitch rate.

      But if changes in yeast character can be best explained by chance instead of fermenter geometry or pressure, then given adequate process control and consistency, a homebrewer should be able to produce identical beers in separate vessels with and without a lid/airlock, or of different depths.

      However (acknowledging anecdotal evidence and the possibility of looser process control than I think) that has not been my experience – particularly with English, Hefeweizen, and a few Belgian strains – and I have found the quality and type of difference in yeast character between open vs. closed homebrew fermentations has been pretty consistent across strain, style, and batch; so I remain a believer.

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