Day 141

No Microbiology lab today–which we only found out when we arrived, so a bit of an annoyance. On the other hand, it gave us more time to rescan our notes for Packaging, since it was time for Doug Pengelly’s “Fun Quiz #1” today. The quiz actually turned out to be a fair reflection of what we have learned over two classes, and the fun part was that we got to mark someone else’s quiz.

Then it was back to learning. Today we continued with carbonation, which not only gives beer its friendly foam head and sparkling bubbles, but also protects the beer from exposure to air after fermentation by forming a layer of gas on top of the beer. Let evil air get into your beer and it can produce stale oxidized flavours in a matter of hours. And there are many ways air can get into the beer: during transfer from the fermenter to other tanks, during filtration, during bottling or kegging, putting a badly fitting cap on the bottle…

We talked about the concept of equilibrium: in a closed container such as a bright beer tank, the pressure of CO2 in the space above the beer and the pressure of the CO2 in the beer will gradually equalize; how long that takes depends on a number of factors, including the surface area of the beer (a smaller surface area will slow down the movement of CO2), temperature, the pressure differential between the two areas, and whether the container is being agitated.

How much CO2 is in your beer? In North America, we talk about “volumes of beer”, as in “there are 2.5 volumes of CO2 in that pale ale” (meaning there is 2.5 times as much CO2 in that bottle as there is beer). Just to make things confusing, Europeans measure CO2 content by mass (grams of CO2 per litre of beer) instead of volume. So just in case sometime during our brewing career we decide to get on the phone and talk to someone in Europe about how much CO2 is in our beer, we derived the formula for conversion from volume to mass. I won’t go through the whole derivation. The short answer is:

 x ( m/V) =  y

x = number of litres of CO2 per 1 L of beer (North American measure)
m =mass of 1 mole of CO2 = 44.0 g
V = volume of 1 mole of CO2 at 20°C = 22.414 L
y = number of grams of CO2 per litre of beer (European measure)

So if I want to tell Hans in Germany that my new stout has 2.5 volumes of CO2, I would quickly calculate:

2.5 x 44.0 g/22.414 L = 4.91 g/L

and tells Hans my new stout has 4.91 g/L of CO2.

We also looked at a couple of pieces of brewery testing equipment: the carbonation tester, which as its name suggests, tells you how much gas is in your beer; and the air tester, which finds out how much evil air has snuck into your beer.

The air tester actually utilizes a chemical reaction that we first heard about last week when we learned the Bad Thing that might occur if you are cleaning a tank that is still filled with CO2: apparently the CO2 will instantly combine with the water in the caustic solution to form carbonic acid. The carbonic acid will then react with the caustic soda to form sodium carbonate, a solid. Poof! What was a large amount of gas inside the tank is suddenly transformed into a few grams of powder on the bottom of the tank. Bang! The resultant vacuum inside the tank will literally cause the tank to implode. Haul that twisted piece of metal out of the brewery and getcherself a new tank.

The air tester uses the same reaction, only on a much smaller scale and without the implosion: you basically fill the glass tester with caustic solution, then vent the gas from a bottle of beer into it. The CO2 will react with the caustic and precipitate out. If there is any air (i.e. nitrogen and oxygen)  in the bottle, it will not react with the caustic, but will simply bubble through the caustic and collect in the top of the tester for you to see. Hopefully you don’t see any air. If there is air, you then take samples from beer along your production line to pinpoint where and how air is entering the beer.

No classes tomorrow. Instead, we’re all off to the Master Brewers Association of Canada (MBAC) annual conference. Includes lunch, and rumour has it that there might be samples of beer at the seminars. If so, it could be the Best. Conference. Ever.

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3 Comments on “Day 141”

  1. Canageek Says:

    This is why I am in favour of using M/L for everything, the math is much simpler then either mass or volume %.

  2. Ben H Says:

    What is the mass fraction of carbon dioxide in beer?

    • Alan Brown Says:

      The amount of CO2 in the beer can vary enormously depending on style. For instance, CO2 in cask ales is likely around 3-4 g/L, in bottled ales is 4.5-5 g/L and in wheat beer can be as high as 6-10 g/L.

      The other factor, likely unimportant if you are rounding to only 2 significant digits, is the specific gravity of the finished beer. If the FG of a cask ale is 1.016 and it has 3 g/L of CO2, the mass fraction of CO2 would be 3.0/1016 = 0.00295 = 0.003 (0.3%)

      A wheat beer with an FG of 1.008 and 9 g/L of CO2 would have a CO2 fraction of 9/1008 = 0.0089 = 0.009 (0.9%)

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