A Modern Lager Brewery - mashing

We're now at the very heart of Lager brewing: decoction mashing. A process that was very different to the mashing schemes usually practised in the UK.

"Mashing.—For the primary mash, cold water is used, and usually, after half-an-hour's stand, boiling water is added, to bring the heat up to 90° F. The most recent practice is to make this mash at such a temperature, and leave it standing for such a period as will conduce to a slight acidification taking place, whereby proteolytic activity is encouraged, with the consequence that a better digestion of the proteins into their permanently soluble form of peptone is obtained. As has already been pointed out, many other variations of the decoction system are practised, with a view to saving time and fuel, but, with the possible exception of the Kubessa modification (in which the three grist constituents, grits, flour, and husks, are dealt with separately), there is little doubt that the original three-mash method, with certain modifications, is still the most generally favoured. That system usually consists of about one-third of the total mash being transferred to the mash copper, and there gradually raised to the saccharifying temperature, then rapidly boiled for a certain period, after which it is slowly returned to the mash tun, where it raises the temperature of the mash to 127° F. This is repeated a second time, when the resulting heat of the mash will be 150° F. On the third occasion, the muddy wort is separated from the more solid portion of the mash, and this is treated in much the same way, the final temperature being about 167° F.

The manipulations in the mash copper vary according to the class of malt in use and the type of beer brewed, and constitutes one of the many points which only a thoroughly competent lager brewer can determine; where, however, a laboratory, provided with a polarimeter, exists, the adjustment of the mashing operations, to give a wort of definite specific rotatory power, should not be difficult.

After the mash has been raised to its final temperature, it is transferred from the mash tun either to the clearing tun, which in many cases is fitted with a water-jacketted bottom, or, as is more general nowadays, to the mash filter, from whence the worts are drawn off into the wort copper, and there boiled with the hops. In brewing lager, the wort is not left in contact with the hops in a hop-back, as is the case in an English brewery; the vessel, through which the wort at this stage simply passes on its way to the pump, is provided with a strainer, only slightly smaller than the vessel itself. The newer forms of this apparatus are fitted with leaching and pressing arrangements. In this connection, it should be remembered that the major portion of the insoluble matters has been precipitated while boiling the mashes, and has been left in the clearing tun or mash filter as the case may be. An open type of receiver, fitted with cooling coil and float valve, is sometimes employed."
Journal of the Institute of Brewing, vol. XVII, 1920, pages 493 - 494.

From the description, it sounds like the first two decoctions were with the thick mash, the last one with the thin mash. This wasn't just a random whim. Most of the enzymes were in the liquid part of the mash. By boiling the thick mash the maximum quantity of enzymes was retained. By the time of the third decoction, this didn't matter as the whole mash was raised to mash out temperature by the final decoction.

Decoction mashing, as practised in Bavaria, was a bit more complicated than just a triple decoction. There were many different methods of even just triple decoction. Most big Bavarian towns had their own specific method.

I'm not sure what effect not having a hop back and not leaving the hops in contact with the wort after boiling would have. The more commercially minded UK breweries pressed the hops in the hop back to squeeze every last drop of wort. Though I'm inclined to believe that this wouldn't have been exactly top-class wort.

Fermentation next time.