The history of beer and the history of brewing technology are separate subjects, while clearly interrelated. In Part I we discussed that until at least the 1930s some newly-built breweries, both top- and bottom-fermenting, employed a double system of cooling the boiled wort.
(Wort is the sugar-rich extract of a barley-based mash. It is boiled with the aromatic and resinous hop, and then fermented with yeast to produce beer. The starch of the malted barleycorn must first be converted to fermentable sugar to permit production of alcohol, unlike the case, say, for wine fermentation. The sugar is ready-made in the grape envelope).
See the Comments where a brewing specialist usefully pointed out that a shallow surface cooler, apart from partially cooling wort, separates well the trub (or sludge) in wort. This is various lipids, proteins, hop debris, and other coagulants whose removal produces a clear wort, generally favoured for fermentation.
The question of sludge separation, the related cold and hot break removals, the reasons therefore and how it was and is done, is far from simple. This is why we have brewing schools and brewing technologies.
Here, I simply want to explain what the 1930s-era Malayan Breweries Ltd. in Singapore and Marine Brewery in Brussels had in mind, as well as older breweries using similar methods, when using the open cooler + heat exchanger.
A representative of the Singapore brewery told a reporter that open cooling, which used purified air in that case, had a beneficial impact on the beer.
Exactly the same thing was stated in 1930 by the great brewing engineer Dr. Leopold Nathan. Nathan was the Swiss-based designer of the cylindro-conical fermenter. Today this equipment is used all over the world in breweries of all scales.
He wrote that year in the Journal of the Institute of Brewing that surface coolers, used in the right conditions, produced an especially fine palate for lager. He explained this meant “volatile” substances in the wort detrimental to flavour, that resulted in an “onion” taste, were removed by the atmosphere.
See especially p. 539, bottom-left corner.
The beneficial effect was greatly assisted by cold, dry, snowy weather as the always-present risk of infection was minimized. He felt lager would not succeed in the U.K. using the traditional open cooler, as its climate was often foggy and humid. The volatiles would condense back into the wort due to these conditions.
His fermentation system had an enclosed tank that received and cooled hot wort over aluminium plates prior to fermentation in what is now called the “conical”. At the time, even for lager brewing his system, some 40 years in the making and now viewed as revolutionary, was just coming into use internationally.
Further, his system had a way to vent fermenting beer of these volatiles, by a scrubbing action of carbon dioxide – I discussed this in earlier writing.
While similar surface coolers were used in the U.K. and in 1870s Australia as noted, the problem of these volatiles was not quite the same. The infection risk remained, but the other was much less important.
The reason is the “onion” taste, a perceived defect in pale Continental beer discussed since the late 1800s, resulted mainly from dimethyl sulphide. DMS as it is known arises from use of very pale malts suitable for lager. His article noted that different materials were used in U.K. brewing, which implied that the problem was not acute there.
The malts used for ale and porter were kilned darker than for lager malt, with the result the volatiles of concern were produced in much lower concentrations. The onion taste did not appear.
Still, the infection risk remained for any form of beer produced, hence Dr. Nathan’s proprietary system that avoided the risks in question.
Traditionally, as Dr. Nathan alluded, long aging in large casks or tanks was employed to allow the objectionable volatiles to escape. Sometimes success was partial though. The use of krausen or newly-fermented beer to carbonate the old also potentially countered the beneficial effect of long aging.
Nathan’s system produced “clean” lager in much less time, with less risk of infection, than the old pan cooler-based and lengthy aging systems.
Even though Nathan fermentation was still quite new, period literature shows lager breweries had other alternatives to the double cooling system noted. These included deep hot wort receivers and various forms of filtration both before and after chilling in the heat exchanger, which itself was undergoing improvement notably by being enclosed.
While 1930s breweries had different options to chill and clear the wort, quality considerations for many still mandated use of the open cooler + heat exchanger (or refrigerator) system.