Sunday 26 July 2009

Coming up for Air

I have very little in the way of formal qualifications in brewing. Up until 6 years ago I had very little work experience in the industry. Before that time my job was to count neutrons. Yes, really. That's right, those incredibly small sub-atomic particles that are impossible to see, and actually fairly difficult to detect owing to their lack of any electrostatic charge. You might wonder how I managed to count them. Well I could tell you, but I suspect I'd have to kill you afterwards.

Now neutrons are significantly smaller than yeast cells. Yeast cells can be seen under a microscope and are significantly easier to count. Also, once you counted the yeast cell it is still normally there. Neutrons, on the other hand, refuse to stay where you left them, and in fact, there is some question about their existence anyway. It is something to do with trees falling over in forests when nobody is there. Something to do with blind faith, although to be fair, there is a little more evidence to support the existence of neutrons over that of God.1

I'm not going to brag about qualifications. I don't believe I need to. What I know is that I have learnt and forgotten more than I have managed to retain as a result of working previously in a highly technical environment. Much of this knowledge is highly transferable and my previous scientific and engineering background has primed me to be able to analyse all manor of diverse technical subjects. I believe brewing can be included as a technical subject and compared to some of the esoteric subjects I have dealt with in the past, something of a doddle.

What I know about brewing is that oxygen is good for getting primary fermentation going. Normally this oxygen is incorporated into the beer as a result of the wort falling through the air into the fermenter after flowing through a heat exchanger, where the previously boiled wort is cooled to pitching temperature. The yeast uses this oxygen as part of it's metabolism during the vigorous primary fermentation and hopefully all this oxygen is consumed, leaving an oxygen free beer. The spoilage bacteria don't stand a chance because the yeast has competed for oxygen and nutrients and by now won with style. It's really a numbers game; billions of yeast cells and only a few hundred other organisms.

The beer is often chilled towards the end of primary fermentation. This enables the CO2 that is being produced by our friendly yeast cells to be dissolved and retained in the beer; the lower the temperature the more volumes CO2 that will be retained. At a temperature of 11-12oC the beer will have a carbonation of around 1.1-1.2 volumes at atmospheric pressure. The beer has to have live yeast in it for this to happen, but providing it is given some time, oxygen is not required for this process to occur. The yeast will settle to the bottom of the vessel, along with any remaining precipitated proteins and other particulates, which might include the vast majority of the unwanted micro-organisms. A small amount, around 5% of the original pitching rate of yeast, is allowed to remain in the beer. Some of this process might or might not be performed in a conditioning tank depending on the brewery.

From this point on, the best brewers will work very, very hard to prevent oxygen coming into contact with the beer. For that matter, eliminating air and therefore spoilage bacteria and wild yeasts is also key. Additionally, if the beer is in contact with oxygen for a significant length of time oxidization of the beer can occur, which most beer connoisseurs consider a bad thing to have happen to your beer. Together, spoilage bacteria and oxygen will react with the beer and create off flavours quickly, adding nothing to the quality of the beer; in any way, shape or form.

Once in cask the remaining yeast will add to the carbonation of the beer. Remaining fermentables allow remaining yeast to progress slow secondary fermentation and a very good cask beer will improve in a sealed cask for weeks, months and sometimes even years. If the beer remains in contact with live yeast it will consume some compounds that result in off flavours.

When it is time to serve the beer it is time to vent the beer. The reason for venting is to release excess CO2 and so prevents the beer from being too lively on serving. Failure to do this can result in overfobbing and too much head, if head is not your thing. There is no requirement at this point to allow air to come into contact with the beer in the cask other than something has to replace the beer that is removed. There is no purpose served in letting damaging oxygen and microorganisms coming into contact with the beer. The conditioning has already been done. If this venting can be done through a one way valve, such as a race spile, then things are wonderful.

If at this point in time a non-pressurized CO2 blanket is allowed to rest over the beer, without any air entering, then the beer could actually last for many days or even weeks as this would be no different to it being in a sealed cask. There is no scientific argument that could be applied against this, in my view. Would it still be classed as cask beer? That's for the reader to decide. My view is that cask beer should be matured on live yeast in the vessel from which it is dispensed and have a relatively low carbonation level. That, for me, would be the end of the discussion, but it won't be, and probably shouldn't be.

I like the beer blogging world. I really like all the people who take time to post and comment in this international, largely constructive medium. I do make an effort to understand the things that are being discussed and it can be surprising to find where the best knowledge resides, although the techniques of getting that across might not always be helpful. I care about all who take part and you all mean a lot to me. Sometimes things get out of hand. Discussions develop that become destructive due to entrenched positions where the sides are obviously taking an "I'm not listening" stance. My mother might have said "If you lot don't stop fighting I'll have to bang your heads together"

What is this all about? Check out this post and this post and ensuing comments.


1Sorry, yes I'm taking the piss out of hardcore physicists a little here, who are similar to hard core beer fanatics and sometimes the same thing. Very few of them, physicists that is, can understand my assertion that nobody has actually proved the existence of the neutron. Beer fanatics probably don't care about neutrons despite the fact that neither them nor the beer would exist without such amazing little things. Rather than proof we just have a model for how sub-atomic particles work and so far nobody has been able to run an experiment that disproves the model. Sometimes the model needs to be adjusted a little as more sophisticated experiments are run. But guys, nobody has ever seen a neutron, we can only observe it's effects.

It's true that the robust model we have of the strange subatomic world is fairly indisputable and better than the "God must exist because you can't prove he doesn't" argument. But most physicists simply have blind faith in what previous physicists have learnt. Sometimes the same can occur in the beer world.

Some days though, I do wonder; is that a yeast cell I can see when looking down the microscope, or am I just plugged into a big matrix so I have no way of knowing what is real and what isn't anyway?

You take the blue pill and the story ends. You wake in your bed and believe whatever you want to believe. You take the red pill and you stay in Wonderland and I show you how deep the rabbit-hole goes. Remember -- all I am offering is the truth, nothing more.


Whorst said...

Dave, well done. If people read that exchange on the links you provided, they'll see it was a bit like Galileo being attacked by the Christian Militia. I have never heard of conditioning taking place via exposure to air. It's an oxymoron.

Jeff Pickthall said...

What was it Mrs Schrödinger said? "What have you been up to, the cat's half dead?"

Gazza Prescott said...

Having cellared beers the "real" way, with hard/soft pegs, and using race spiles I can comment on both I feel.

Race spiles almost always result in green-tasting (appley) beer as any fermentation in the cask has been halted or at least majorly curtailed by the lack of exposure to air. The same, if not worse, goes for blanket pressure where, if the beer's not pegged properly first, results in crap green beer with no development of flavour; allow it to condition first then apply a breather and it's fine, but to rack a cask then apply a breather is a recipe for crap beer in my book.

yes, conditioning goes on in a sealed cask, but it's the final phase when the cask is stillaged and then vented that makes all the difference as to what it finally tastes like. I'm no Camra apologist and I support cask breathers, but after many years of experience I feel cask ale needs a day or so soft/hard pegged to gain it's soul.

Unknown said...

Gazza, although I have no doubt that the effects you perceive are real, there is no basis in science for it to be due to air getting at the beer. The amount of air getting at, say, 72 pints of beer through that tiny hole is going to be very small indeed. If it is pegged with a soft spile the only thing that will happen is that CO2 will escape as there will be a small but present positive pressure inside the cask. Eventually air will get in, after a couple of weeks, but by then your beer will be flat.

My guess is that what you perceive is over-carbonation due to slower gassing off. Over-carbonation does seem to drive off volatiles during dispense by hand-pull that can effect the drinking experience.

Beer does not ferment after the cask is vented. Why do you think it does? I'd be interested in the microbiological and fluid dynamics principle when applied to the volumes in question.

Andy said...

Dave, I wonder if part of the confusion with the debate is what we actually mean by "conditioning" I suspect some people incorrectly consider "conditioning" to relate purely to levels of carbonation as you suggested in your reply.

I agree with your definition - that conditioning is indeed the impact of the secondary fermentation on the development of the beer. In fact one of the purposes of that secondary fermentation is to purge out unwanted substances such as oxygen. So the addition of oxygen has no place in the development of better beer flavours (post fermentation). In fact the more careful you are avoiding oxygen uptake while transfering beer at the end of the fermentation cooling stage the less crucial the role of the secondary fermentation itself (but obviously it's still important) Personally I prefer the term maturation of the beer as I think it more clearly defines what we are trying to achieve (which could include hop flavour development from dry hopping)

If it is indeed as Gazza states "the final phase when the cask is stillaged and then vented that makes all the difference as to what it finally tastes like" then perhaps we shouldn't argue too much as it gives brewers an easier get out clause if a publican complains about the beer!!!

A question to the oxygen is good brigade might be: When drinking bottle conditioned beer do you open it a few hours beforehand and vent it?

Unknown said...

Andy, agree 100%

Dry hopping - mmmmm - I like dry hopping. But doesn't it make it a bugger of a job to clean the casks?

Brewers Union Local 180 said...

Pellets mitigate the cask-cleaning problem.

It's the oak chips that are a bugger.

Whorst said...

Comical to say the least. I'm still laughing. Goes to show you can be heavily engaged in the scooping art and still not have a clue about what you're talking about.

Gazza Prescott said...

Maybe I misphrased my reply, but I've had beer which has been stuck under a breather straight away after tapping and it stays very green; maybe it's the Co2 not coming out, maybe it's something else, but all I know from experience is that a beer pegged properly with access to "proper air" not bottled stuff will mature and condition far better.

Obviously some of this is the bugs in the air which are absent in the bottled stuff but it's not all that and, in my opinion, cask beer needs venting to atmosphere to condition properly. Once it's conditioned then you can stick a breather on it and it'll last a week or so but at the cost of flatness and cardboard tastes coming in.

And sausage man is still acting the twat, I see, yet still fails to show that he knows anything about beer whatsoever. Trolling on forums is all well and good, but the moment you show anything that passes as knowledge and/or intelligence will be the day I'll bother reading what you write.

Whorst said...

Prescotti, what in the hell are you talking about?? You've got a pretty big pair of balls claiming I don't know anything about beer. Especially coming from a clown like yourself who doesn't even know how cask ale is conditioned. You can't even explain the science behind your half baked, stupid ideas. Everybody knows you're just trying to save face, after you've clearly hung yourself. Go scoop another 20,000 beers and get back to us.

Unknown said...

Now then both, the words are starting offend me. Please, the issues are fair game, but tone down the language or I'll have to start moderating.

Gazza, I wonder if cask breathers, as made today, incorrectly control the venting off of carbon dioxide. There has been little development of such devices due to their universal condemnation. I'm convinced, as are others, that air is ONLY harmful to beer. Of course, the taste of cardboard is one effect of air.

Actually, I know Wurst has upset Tandleman and yourself quite a lot. Really though, I had a long conversation with him on the telephone a few days ago and really he's not what you make him to be, honestly. Perhaps his piss taking is out of order, but he really does know more than you make him out to.