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09-02-2016, 07:20
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https://1.bp.blogspot.com/-_m0IP0gJ6J4/VrSIevS4tBI/AAAAAAAAZN8/uy7dnnb3jmE/s400/John_Richdale_Brown_Ale_1948.jpg (https://1.bp.blogspot.com/-_m0IP0gJ6J4/VrSIevS4tBI/AAAAAAAAZN8/uy7dnnb3jmE/s1600/John_Richdale_Brown_Ale_1948.jpg)
As promised, we’ll be looking at carbonation. Though obviously, as a lifelong CAMRA member, I consider artificial carbonation to be the work of the devil.

You’ll note that the beer still hasn’t quite finished with its time in a tank. Once it was done with the warm tank, it went to the cold tank.

“On its way to the cold conditioning tank the beer is usually chilled by a counter-current chiller which reduces the temperature to 33-34º. This may consist either of a series of concentric pipes; through the inner one flows the beer and through the annular space between the inner and outer tube cooled brine is passed in the reverse direction; or of a machine similar in construction to an enclosed wort refrigerator. The beer passes on one side of the grooved plates and the cooled brine through the other. This plant, like its counterpart the wort refrigerator, gives very efficient heat transfer; it is easily adaptable for changed loads, as further plates can usually be fitted if an increased output is required; and it is easy to dismantle and clean. Alternatively in some installations the beer is blown without chilling into the cold tank, where it slowly attains the temperature of the cold room. In some breweries where it is desired to prime the bottled beers for sweetness only the practice is to put no priming in the conditioning tanks, but to inject it into the beer as it passes through the chiller into the cold storage.”
"Brewing Theory and Practice" by E. J. Jeffery, 1956, pages 338 - 339.
I’ve already explained a little about wort refrigerators. They were an important development in the late 19th century, allowing wort to be cooled much more quickly. Especially in summer, when during warm weather cooling in an open cooler could take many hours, during which time the wort was vulnerable to infection.

I guess leaving it to cool down in the tank used less energy, but took longer.

Now the exciting act of carbonation itself:

“It is at this stage that carbonation takes place. The carbonation may be effected as the beer passes from chiller to cold tank or by carbon dioxide top pressure in the cold tank. In this case assimilation of the gas is slow unless some form of rousing is installed. Finings, if used, would be added to cold tank before running in the beer. A rouser is sometimes installed to assist in mixing-in the finings, but usually the motion of the beer as it enters will give adequate mixing. Without rousing, absorption of carbon dioxide may take two or three days, whereas with efficient mixing it may be complete in about an hour. There is one system which uses the same tank for conditioning and cold storage (sometimes these periods are referred to as warm and cold conditioning respectively) and the tank has a propeller for rousing, so that absorption of the gas in the second (cold) stage is accelerated. When, as is more usual, separate cold tanks are used they are not generally fitted with mixing devices. ”
"Brewing Theory and Practice" by E. J. Jeffery, 1956, page 339.
It’s striking to me that at this point the beer still hasn’t been filtered and could be fined at the same time as it was being carbonated. Filtering only occurred later in the process. But we’ll be getting to that later.

I would have thought that swirling the beer about with a rouser would have knocked CO2 out of solution rather than help it be absorbed. But what do I know?

https://4.bp.blogspot.com/-f7phXUvGX7U/VrSIob44QwI/AAAAAAAAZOA/-BMJKil_cdo/s400/John_Richdale_Nut_Brown_Ale_1948.jpg (https://4.bp.blogspot.com/-f7phXUvGX7U/VrSIob44QwI/AAAAAAAAZOA/-BMJKil_cdo/s1600/John_Richdale_Nut_Brown_Ale_1948.jpg)Carbonation has changed a little over the years. It does still sometimes take place as the beer is being chilled:

"This addition of carbon dioxide can occur whilst chilling beer through a plate heat exchanger and so can take advantage of the turbulence of the beer in creating good conditions for gaseous exchange. A purpose-designed carbonation unit can also be used. This consists of a long pipe usually in the form of U-tube bends through which the beer flows. Carbon dioxide is injected as fine bubbles and the uptake, even in this form, can take a considerable time. The carbon dioxide must be the purest form available and no oxygen must be introduced. The injection unit must be easy to clean and must be cleaned regularly. Carbon dioxide can also be added `in-vessel' but this is frequently less efficient and more difficult to control. A `carbonation stone' is sometimes used to ensure production of fine bubbles of carbon dioxide to aid dissolution in the beer. This technique is sometimes described as `gas washing' and provides an opportunity for the removal of oxygen and unwanted flavour volatiles as well as carbonation. After `washing' the vessel must be sealed to allow pressure build-up and the dissolution of carbon dioxide. There are a number of problems associated with externally added carbon dioxide and it is good practice to avoid this technique as far as possible."
"Brewing Science and Practice" by Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes and Roger Stevens, 2000, page 564.
But note that “externally added carbon dioxide”, i.e. CO2 added by top pressure in the tank, is no longer recommended.

Finally this is how much gas to add:

“Carbonation is usually effected so as to give a carbon dioxide contact after bottling of about two volumes of the gas per volume of beer or 0.4% by weight of carbon dioxide. To allow for inevitable losses during bottling it is advisable to carbonate to the extent of 0.5% by weight, which requires a pressure of 2.6 lb. per square inch at 33° F.; 3.3 lb. at 34º F. and 4 lb. at 35º F.”
"Brewing Theory and Practice" by E. J. Jeffery, 1956, page 339.
The pressure needs to be higher if the beer is warmer because CO2 is more soluble at lower temperatures.

Next it’s how to store your chilled beer.

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