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.
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"
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.