Sunday, 17 April 2011

"Do you believe force carbonation gives a different kind of fizziness as opposed to bottle conditioning?"

In the comments on my previous blog post, Dom of Thornbridge brewery asked: "Do you believe force carbonation gives a different kind of fizziness as opposed to bottle conditioning?". This is the sort of question that is so innocently placed that it must be a trap, but nevertheless, I'm going to have a stab at answering it.

I'll preface this by saying that I'm going to talk in broad-brush terms, employing generalities to which there may be exceptions. However, what I say is what I think, and it's born of experience and education, although perhaps someone more expert than may might chime in with an opinion. It's also appallingly geeky, for which I don't apologise, but I do warn you that unless you find the title of the post interesting, the next 400 words will be a tad dry.

My gut feeling is that force-carbonating and bottle-conditioning do produce different types of fizziness. There may be some overlap between them – bottle-conditioned beer can be overcarbonated, and a filtered beer that is undercarbonated is particularly lifeless, and vice-versa - but in the main, they are different.

My drinking experience tells me that bottle-conditioned beers generally have a finer, softer carbonation than force carbonated beers. That's not to say that it's always preferable – I find the supersaturation of CO2 in many Belgian beers a bit hard to deal with, but again, this is a fine, small-bubble type of carbonation, whereas I find force carbonated beers tend to have larger, rougher bubbles. This is my experience, but there's also a bit of science behind it.

When sparkling wine is made, it can gain carbonation either from being fermented in a large closed container (tank, cuve close, or Charmat method), or it may be refermented in bottle (the so-called methode Champenoise). While both of these processes make fizzy wine, the methode Champenoise is generally accepted to produce smaller, more persistent bubble than the tank method. That's the science – I don't know exactly why, but I'd guess it's something to do with ratios of gas to liquid, and overall pressures producing a certain style of saturation, but that's only a guess.

One other thing I've learnt from homebrewing: the way a beer carbonates has a definite gradient to it. When you bottle a beer with a bit of sugar and live yeast, the yeast eats the sugar and produces CO2 in the the tightly capped bottle. What I've found is that the yeast produces CO2 faster than the beer can absorb it. So after two days, the beer is a riot of barely-dissolved CO2. In fact, I'd guess that the CO2 to conditioned the beer is produced within three days of capping the bottle – the rest of the conditioning process is about the CO2 dissolving into the beer.

Of course, what is actually happening in the bottle is just one thing. How the beer arrives in the glass is another. You can always pour a non-BC beer a bit more roughly, knocking the gas out of it. This does two things (for me) – it makes it less gassy (duh), and it makes it more tasty. It's more tasty because when the beer hits the tongue, if you've knocked a lot of the gas out of it, it doesn't erupt in a riot of bubbles, more beer stays on your tongue, and the flavour is more apparent.

So yes, I do think that force carbonation gives a different sort of fizziness than bottle-conditioning, and that's why.

Geek-out over.



  1. Hahaha, you are right in my opinion, different but not always better...but sounds like you want a fully fledged fight from people with a post on this topic :P

  2. It's nonsense of course. It's not the method of carbonation that determines the fizziness. That is in the past, and unless we're being homeopathic about this (saying that beer has a memory), or that some kind of bubble time travelling is involved, we can discount it.

    Levels of dissolved CO2 being equal, it's the details of bubble formation that are going to be important.

    It's probably significant that force carbonated beverages will often have been filtered and contain less in the way of particulates to act as bubble nucleation sites. I can see how this might contribute to the reported difference in mousse consistency and mouthfeel reported by some.

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  4. While it doesn't go into detail about force carbonation versus bottle refermentation, Mark Denny's book: Froth, The Science of Beer has an entire chapter devoted to bubbles.

    Think the nucleation site comment above is a good one, though things like beer viscosity/density play a major role, as do the surfactants responsible for bubble formation.

    Robert MacPherson and David Srolovitz are the gurus to read up on in the field of bubbles...

    Agree with StringersBeer... it's perhaps not so much the method of carbonation itself, but what is left in the beer and the molecular impact that has on the geometrical dynamics...


  5. Stringers - isn't that a bit like saying "there's no difference between nitrates and organic compost, they're all chemicals"? Clearly the chemistry (and/or physics) of the beer as a finished article is what we're talking about, but that doesn't mean we can't say that production method X has a tendency to produce flavour profile Y.

  6. Stringers - I'm happy to admit that I'm only speculating, although reading my post and your response, it's clear that the question I'm answering is actually "Is there any difference in the perceived carbonation in bottle-conditioned vs force-carbonated beers?", and that's not strictly the one that Dom posed. As I say above, there clearly is a qualitative difference, if not a quantitative one.

    I can see that filtration would have a huge difference on the beer, and as you and Kelly point out, there are more dynamics going on in carbonated beer than just the amount of dissolved CO2. It's clearly also about how the CO2 leaves the beer that produces the impression of fizziness, and that's hugely affected by the physical properties of the beer. Do I believe force-carbonation gives a different kind of fizziness as opposed to bottle-conditioning? No. Does bottle-conditioned beer have a different sort of fizziness compared to force-carbonated beer? Yes, clearly.

    I wonder how that applies to cava vs champagne (or as I shall now refer to it, bottle-conditioned wine)?

  7. Dominic, Thornbridge18 April 2011 at 13:48

    The question you answered is the question I was asking, Zak. Sorry for placing the question maliciously. I was feeling mischievous.

    And you'd be right. Whilst CO2 is indeed the same compound whether applied to the beer through the bottle conditioning process or through force carbonation, CO2 must be given the opportunity to dissolve in the beer - tight bonding of the CO2 solution takes time. So poorly executed force carbonated beer can indeed be described accurately as 'coarsely carbonated' when its bubbles are annoyingly large, and a bottle conditioned beer, done well, is something to behold.

    I congratulate you on your convictions, dear fellow. Yours is a bottle of something nice the next time I see you.

  8. Completly agree with you. Is it maybe even a case of its quite hard and expensive to get 100% pure co2 to carbonate a beer with, where as yeast will only produce 100% co2?

  9. One of the local brewpubs in this part of Virginia uses a German method of natural carbonation called "spunding" - basically when the primary fermentation is about 1 degree Plato from the target gravity, the fermenter is sealed, thus all the CO2 produced by the yeast carbonates the beer rather than escaping through an airlock. I find that the fizz of the beer is less spiky (thoroughly untechnical term I know) than force carbonated beers.

  10. Therefore, the next logical (interesting?) question would be:

    Do you believe that the yeast strain used to bottle condition a beer impacts the kind of fizziness?

    Based on Dom's response above, the obvious answer would be no. But, Kelly says:

    "it's perhaps not so much the method of carbonation itself, but what is left in the beer and the molecular impact that has on the geometrical dynamics..."

    Something like Brett, for example, being able to break down and consume long chain sugars and starches, would that change the 'build up' of the beer sufficiently to change the appearance of the carbonation?

    And ... is there not variation in the amount of CO2 produced as a product of fermentation depending on the yeast strain doing that fermentation? Brett being accepted as one that produces less CO2 than ale strains for example.

    Then there's variation in attenuation from one strain to another. That’ll change the amount of CO2 surely etc etc ...

    One question I’ve always had is about krausening. Why is that the krausened beers (I’m looking at you Marble and Moor) appear to have a much softer, more cask-like carbonation that bottles primed with sugar? Does the type of sugar impact the type of carbonation?

    Suddenly I feel the need to quote Zak:

    "It's also appallingly geeky, for which I don't apologise"

  11. Dom - but surely then there's a gradient where FC and BC beers become equal? And does temperature during the period when the CO2 dissolves make a difference to the final result? And yes, you did a good job of making me squirm, and yes, I did back-pedal a bit!

  12. Phil - carrying on with your analogy, there's no demonstrable difference between nitrates (in an "inorganic" fertiliser) and the nitrates contained in lovely organic manure. Of course lovely organic manure contains all kinds of stuff other than nitrates, and is usually applied as part of a system very different from those which rely on "chemicals".

    ZakAvery - I'm sure that you can tell the difference between force and naturally carbonated beverages - I'm not suggesting that you're deluded. But we can be pretty sure that it's not how the CO2 got in that's making the difference. Otherwise we'd be having to throw out an awful lot of post-enlightenment science. Let's not do that without some more convincing evidence.

    I don't believe that yeast sits at the bottom of a bottle giving out a tiny stream of bubbles like a microscopic carbonation stone, which CO2 then accumulates in the headspace, gradually dissolving back into the beer. The poor little beggars would inflate and explode rather - like tiny little balloons.

    As I remember (and here I'm going back to my childhood... childhood... childhood...) is that CO2 produced by yeast is converted to hydrogen carbonate by yeast enzymes (carbonic anhydrases) fairly quickly. i.e. it is dissolved pretty much as it is produced.

    What happens to it then depends on all kinds of things - pressure, temperature, pH - that kind of stuff - and it can start coming out of solution again. And perhaps dissolve again. The non-enzymatic reaction is relatively slow.

    Incidentally, carbonic anhydrase in saliva is part of what makes carbonated drinks fizzy. The reaction goes the other way (hydrogen-carbonate -> CO2) more quickly in your mouth than it does in your glass.

    Bottom line, at equilibrium, CO2 dissolved in beer can be completely described by a relatively simple system. Bubble formation, on the other hand, is quite a wiggly thing.

  13. Dominic, Thornbridge18 April 2011 at 19:58

    Zak, it's certainly to possible to carbonate a beer slowly and get a similar bubble/mouthfeel combo. Carbonisation units in grown-up breweries and packaging plants atomise the CO2 as finely as possible to help dissolve the beer. Temperature and pressure have influences on dissolved levels but I don't think they have much relation to bubble size. A more grown-up brewer might know.

    Mark - Krausening is a separate and more interesting topic, something you should research yourself. Or I might e-mail you about it soon. And Brett's not often used to carbonise beer. One thing that is accepted is that the yeast strain used to condition a beer generally doesn't affect the beer flavour (except if it was Brett...)

    Velky Al - There are German breweries that collect CO2 during fermentation and then inject it back into the maturing product. This is considered fine by the Reinheitsgebot. Although, I like the idea of Spunding better for some reason!

  14. Stringers - on that evidence, I think it's fair to say that I have only a broad-brush understanding of the topic.

  15. Krausening is something I've "studied" (in the loosest possible definition!!), but for homebrewers it's pretty much a non-starter because we don't brew enough (or enough of the same beer) to really make it possible.

    The priming yeast strain might not affect the flavour of a beer (unless its brett), but could it change the carbonation appearence in the ways I wrote about above? Im guessing Im just taking things a bit too far and unless you're using something extreme like brett, the difference in things like CO2 production per unit of fermentation would be so small that you'd never notice them.

    Ahh beer, such a simple beverage!

  16. Stringers and Kelly are on the money when it comes to the science. That said it is impossible to quantitatively measure people's experiences of carbonation in beers. CO2 must obey Mr Boyle, even in beer. If you use mineral water as your model, Pellegrino has a much lower carbonation than Tesco value and hence is less aggressive on the palate. Equal levels of CO2 in beer can feel different because of what is dissolved in the water and ethanol. If you add N2 to the beer you vastly reduce the gassy sensation of the beer even at the same level of CO2.

    Intensively filtered, high adjunct, high gravity-brewed lager with 2.2 vols CO2 = Gassy

    Bottle conditioned unfiltered barley wine with 2.2 vols CO2 = smooth

    Strong highly hopped, rough filtered, IPA style beer with 2.2 vols CO2 = soft and creamy

    Famous Belgian Tripel made by Monks = 3.3vols CO2

  17. I was told recently that sparkling water is the best way to hydrate whilst on a session due to the bubbles? Can the scientific minds of Mssrs Ryan, Driscoll and Howe confirm if I've been correctly informed?

  18. Jesus, this is geeky and I love it! Although the only word is really, fully understand is 'bubble'...

  19. Dominic, Thornbridge19 April 2011 at 09:28

    Stuart - thanks for putting it better. I was going to use the v/v example but couldn't be bothered checking...
    Fletch - did West Lancs CAMRA tell you that? Or a 'Sports Scientist' (widely regarded as the lowest form of science, close to 'Religion' etc)?

  20. No, no thank you Dom.

    Mark, carbonated beverages do cross the stomach lining faster than flat ones. I suppose it depends what kind of session you are having. Sex and excersize are seldom improved by a bloated stomach or flatulence. If you are drinking beer which is less than 8% ABV you should be getting enough water to keep you hydrated while you are drinking, it is when you stop you need to keep the fluids up. Salts are then probably more important than CO2. If you stick to beer at 3.4% ABV or less you are hydrating more than you are dehydrating.

  21. Stuart, thank you kindly. New rehydration rules are as follows: peanuts with pints at the pub, San Pellegrino with a dash of Gatorade for post-Trappist drinking, and pineapple juice pre... I'll leave it there!

  22. Force carbonation is a combination of the lbs of pressure and the temperature of your beer. The colder it is, the less lbs you need. When you are force carbonating, you need to shake the keg until you can no longer hear the hiss of your c02 tank, which usually takes a few minutes.


Sorry about the word verification - the blog was getting spammed to bits.