Saturday, 19 October 2013

Natural vs. artificial CO2

Just because I've finally laboured my way through Hartley's piece on bottling, it doesn't mean you're off the hook. Far from it. I've just moved on to the next article.

It's from a particular favourite of mine H. Lloyd Hind and was written in 1922. I'm going to give the descriptions of the soaking and scrubbing machines a miss, at least for now. Because I want to look at CO2. And the difference between the stuff was given off during fermentation and that created artificially.

How many times have I seen the argument CO2 is CO2? Usually when someone was poopooing the idea of the CO2 in bottle-conditioned beer behaving differently from that in artificially carbonated beers.

"Of almost equal importance with brilliance is condition, and there are several points which must be considered both for naturally conditioned and carbonated beer. Two may be referred to, viz., natural versus artificial gas and temperature at filling, for both have been neglected in many directions in which their study would be well worth while. Purity of the gas and freedom from air is on essential, whether it is made from coke, chalk and acid, or collected from the square. In either case it can readily be obtained of 99.8 per cent, purity, and the bottler should always assure himself by test or otherwise that it is so. Air in the gas leads to troubles, greyness, development of organisms in the beer or poor condition.
Journal of the Institute of Brewing, Volume 29, Issue 3, March 1923, pages 121 - 122.

Contamination of your CO2 with air has the obvious downside of giving nasties something breather. Not a good idea if you preferred your beer uninfected.

There was one clear advantage of collecting CO2 from your fermenting vessels: you got it for free. Well, free other than the cost of collecting and storing it. And fermentation provided a superfluity: one barrel of beer produced enough CO2 during fermentation to carbonate several barrels.

"The production of the gas is a matter for the brewer and need not be discussed now, but the bottler is very much concerned in its quality and cost. It can be supplied to him at a price lower than that of artificial gas and at the same time give a good return to the brewer for outlay and upkeep. It is not only useful for carbonation, but much to be preferred to pumps or compressed air for moving beer from tank to tank, for the pressure required for the filter and other purposes. For all these there should be ample from the brewery as enough gas can be collected from one barrel of beer to carbonate eight barrels. With such a supply and so often going to waste its utilisation should be worth the closest attention from both brewer and bottler, and the more so when the superiority of the natural fermentation gas over the artificial is realised."
Journal of the Institute of Brewing, Volume 29, Issue 3, March 1923, page 122.

I hadn't realised that they were using CO2 to move beer around the brewery this early. Obviously a good idea, gven the unpleasantness that could be communicated to beer through air.

The following passage brings up a point I had never considered. And the main reason I bothered to use this article. The flavour of COs, or rather the flavour of the impurities mixed with it.

"Carbonic acid from whatever source when perfectly pure is neutral in flavour, and this applies to fermentation gas just as muoh as to artificial gas, with this very important difference. The impurities in artificial gas, other than air which may occur in both kinds of gas, are definitely harmful and objectionable and have to be completely removed before the gas can be used. On the other hand, the impurities in fermentation gas, apart from tho air which must be removed, are not only harm less but the very substances which the beer requires to give it the snap and flavour of naturally conditioned beer. It is sufficient to smell the gas coming from the fermentation of a fairly strong beer to realise how very much superior it is to artificial gas for carbonation. The volatile constituents from the wort and the essential matters from the hops are very pronounced and impart their flavour to the beer into which the gas carrying them is injected. This in itself would be enough to stamp the fermentation gas as superior to the artificial, but when to this is added the experience that in practice it gives a beer with a more lasting and solid head and a beer which drinks fuller, the choice of fermentation gas is more than ever confirmed. Tasteless gas can be much improved by passing through a large cylinder packed with hops.
Journal of the Institute of Brewing, Volume 29, Issue 3, March 1923, page 122.

Now there's a turnup - the impurities in natural CO2 actually enhanced the flavour of the beer. Not just that, Lloyd Hind asserts that naturally-produced gas formed a better head and a fuller palate. Was that just when formed during bottle-conditioning or whenever naturally-produced gas was used? I think he means the latter. And what about passing the gas through hops - what would you call that? Gas hopping??

Remember that bit in the last article about CO2 getting "burned"? Lloyd Hind seems to agree that excessive pressure and heat damaged the flavour of CO2. Though he doewsn't explain why that might be the case.

"The bottler being in the position to command a supply of gas direct from the brewery he must assure himself that it is always of the desired character. It is quite simple to make sure that it contains no more than 0.2 par cent, of air and that it has no undesirabloe flavour or smell such as might arise through unsatisfactory conditions of fermentation which are quite outside of his control. Pure gas will keep indefinitely but to conserve the very desirable and delicate aromas of fermentation gas and make sure that no undesirable changes occur in them the gas must be used fresh, a week's stock at the most should be ample. There is no object in having the gas liquefied when the brewery is near at hand and the gas can be delivered down a pipe to a storage tank. Indeed, the liquefaction of the gas is more or less harmful, no pressures above 250 lb. to the square inch should be used in the storage tanks. Compression of gas means heating it, and however good the cooling arrangements on the compressor may be higher pressure than 250 lb. is to be avoided. Heat entirely ruins the flavour of the gas, and the user must assure himself that it has not taken place. The presence of oil and impurities of that sort must also be avoided, and if the supply pipe is under the bottler's control he should see that it is kept clean."
Journal of the Institute of Brewing, Volume 29, Issue 3, March 1923, page 122.

Wow. I never knew there was so much to CO2. Especially not that there were different types.

Next time we'll be looking at naturally-conditioned bottled beer. Something the brewing professionals keep insisting is superior in flavour to force carbonated beer.


Ed said...

'Gas hopping' is a great find! I wonder how long before Brewdog invent it?

Gary Gillman said...

This makes sense but as always it is a question of degree. For example, say you had a pint of flat strong ale - naturally conditioned, 7% ABV. Assume it tasted fine but lacked even moderate bubbles. I would add enough neutral-tasting petillant water to bring it down to 5%. Guaranteed the ale would taste great. If the bubbles were too "big" a bit of hard swirling would reduce them to size. Result: a pint of excellent conditioned beer, draught style. Would it be as good a pint of ESB or other natually made conditioned beer? Perhaps not but for practical purposes most would be very satisfied with it. I have done this countless times with great success. Another solution is to blend two beers, one flat, one very fizzy. Oops, the Irish used to do that for draught stout, didn't they?


Jeff Renner said...

Some ten years ago or so,
Anheiser Busch made a big deal of supplying super-pure CO2 for serving Budweiser. This seems pretty unnecessary when you consider that a keg is not on tap for very long in the average pub, but it seemed like a good idea to me as a homebrewer, when I may have a keg on for weeks or months, especially strong beers. I have wondered if there is a small amount of O2 in standard CO2 that leads to oxidative staling, or if, when I think it's happening, that it was from the introduction of O2 earlier in my brewing process.

I hate bottling, but the 1.055 extra stout (25% brown malt) that I just kegged will be on for several months. I should have sucked it up (so to speak) and bottled, I suppose. It could have kept and perhaps even improved for years.

GeoffL said...

That's why Jean De Clerck (A Textbook of Brewing, Vol. 2, 1958) recommended tasting the sample water that the CO2 bubbled through as the last of the tests, after calculating the amount of 'foreign' gas in your supply. Taste was the final decider.

German brewers were always restricted from using any CO2 for carbonation not given off during fermentation in their own brewery by their interpretation of the Reinheitsgebot.