The Decoction or Thick Mash Method

American Handybook of Brewing 1902

According to Thausing, modern beer in Germany and Austria is brewed according to the decoction method with three mashes, while formerly three different systems were distinguished and known as the Vienna, the Bavarian and the Bohemian.  This distinction has become obsolete, since at present in Austria, especially in Vienna, as well as in Bohemia and Germany the decoction method with three mashes is universally employed.  Here and there slight changes are made in certain breweries in regard to the temperature periods and the time of boiling the mash without, however, any perceptible differences in results as to the character of the beer. 

The initial or doughing-in temperature is about 28° to 30° R. (95° to I00° F).  If hot water is run in, it should be done slowly and while keeping the mashing machine moving, so that this proceeding will take 15 to 20 minutes. 

Three parts of the whole mash are successively boiled and called the first, second and third mash, each for 10 to 45 minutes.  In Bohemia, where pale beers are the vogue, boiling is often restricted to 10, 15 or 20 minutes, in Vienna generally 30 minutes, in Bavaria often 45 minutes. 

As to heating the mash in the kettle, experience shows that this should not be done too quickly, but that on the other hand, it is not only a waste of time, but also may impair the quality of the beer, if the mash is left for a prolonged period at low temperature, i. e., heating it too slowly.  This heating is governed to a certain extent by the qualities of the malt.  The method of heating is most important with the first mash, which, in the three-mash process, is run into the mash kettle at a temperature of 28° to 30° R. (95° to 100° F.), and there frequently raised to 40° to 45° R. (122° to 133° F.) by the remaining water. 

This thick mash is then raised in 20 to 30 minutes to 6o° R. (167° F.) and in 10 to 15 minutes more to a boil. To prevent scorching, the stirrers must be kept going until boiling begins. Where imperfect stirring devices are in use the temperature is not uniform throughout the mash, but higher at the bottom and near the sides than is indicated by the thermometer in the mash. 

Enough of the thick mash was run into the pan to bring the total mash in the mash tun (first mash) to 40° to 42° R. (121° to 126° F.) by pumping it over.  The mash should be pumped neither too fast nor too slowly.  What is said about heating the mash applies here as well.  About 15 minutes may be taken for this work.  

The mash having been well worked through, a sufficient quantity is again run into the mash kettle so as to bring, upon return, the total (second) mash to 50° to 52° R. (144° to 149° F.)  Part of the first mash having remained in the pan the second mash generally has 50° to 55° R. (144° to 156° F.) at once upon reaching it and can be so heated that it comes to a boil in 15 to 25 minutes, according to the malt.  

The first two mashes are thick mashes.  By keeping the mash machine going while the mash runs into the pans, much of the thick part of the mash passes into the pans. Brewers formerly were particular to boil very thick mashes, thinking thereby to make the beer very full to the palate.  The third mash is generally a “lauter” or thin mash. Before running it from the tun the mash is allowed to rest for a while, permitting the solid parts to settle to some extent, whereupon the mash is run off so as to get as much clear mash as possible into the kettle.  Brewers used to put a strainer before the outlet and, in some brew- houses, to drain off the “lauter” mash through the false bottom.  At present, the distinction between thick and “lauter” mashes is not often made, and frequently three thick mashes are purposely boiled.

The third mash is brought to a boil as quickly as possible, usually in about 15 minutes. The quantity is to be taken so that the main mash reaches 6o° R. (167° F.) by pumping up the “lauter” mash from the pan. This last operation is called “final mashing.”  It is followed by pumping the mash into the strainer (Lauterbottich), where it is kept in motion for some time by crutches or stirring machine to enable the grains to settle uniformly.  

The decrease of diastatic power in the decoction mashes according to Lintner is considerable.  (Zeitschrift f. d. ges. Brau- wesen, 1888, p. 317.)  If this power at 28° R. (95 o F) is designated as 100, it was found to be 61.1 at 42° R.(126 o F), 26.8 at 49.8° R.(144 o F), and only 26.8 during the straining period (167o F).

The mash having been brought from the mash-tun to the strainer (Lauterbottich) is left to stand.  Then the wort is strained and the grains sparged, using the same general precautions already described for the respective processes in the production of American lager beers.

The wort is generally boiled in the kettle until it shows a good “break”,  then one-half of the hops is added, and after one hour’s boiling the second half, which is boiled for an hour to an hour and one-half more. Total length of boiling with hops, two to two and one-half hours.  Sometimes one-half of the hops is added as soon as the wort boils, one-quarter after one hour, the last quarter one hour before running out.

According to Thausing (Malzbcreitung u. Bierfabr., 1898, p. 609) the amount of hops used for the different types of beer is generally given per hectoliter (about 25 gals.) of wort, mentioning the saccharometer indication of the wort.  For Bavarian beer, to one hectoliter beer of 12.5 to 14.5 per cent, hops to the amount of 0.20, 0.28 to 0.30 kg. are used.

For Vienna beers the quantities of hops per hectoliter used are as follows (1 kilo = 2.2 pounds):
For 10.5 per cent sacch. indication      0.20 — 0.22 — 0.26 kg
For 11.5 per cent sacch. Indication      0.25 — 0.28 — 0.30 kg
For 12.5 per cent sacch. indication      0.30 — 0.33 — 0.36 kg
For 13.5 per cent sacch. indication      0.32 — 0.36 — 0.40 kg
For 14.5 per cent sacch. indication      0.38 — 0.40 — 0.42 kg
For 15.5 per cent sacch. indication      0.40 — 0.45 — 0.50 kg

For Bohemian beer the quantities of hops per hectoliter are as follows:
For 10.5 per cent sacch. indication      0.30 — 0.35 — 0.40 kg.
For 11.5 per cent sacch. indication      0.35 — 0.40 — 0.43 kg.
For 12.5 per cent sacch. indication      0.42 — 0.46 — 0.50 kg.
For 13.5 per cent sacch. indication      0.45 — 0.48 — 0.55 kg.

The boiling of the wort in the kettle, as well as the mashing in the mash pan, is as a rule still accomplished by means of direct firing, but steam heating is more and more taking its place in breweries of modern construction, since brewers have become convinced that the claims as to superior quality of beer from fire-boiled worts rested on prejudice. The amount of coal needed in steam heating compared to fire heating for the boiling of mashes and wort is about two to three.  The amount of steam, according to Thausing, needed for this work, based on actual tests, varied from 36 to 54 kg. per hectoliter wort, which, based on an evaporating effect of 7.5 kg. would mean 4.8 to 7.2 kg. of coal per hectoliter, or about 13 to 20 pounds per American barrel, which figure is to be increased by 50 per cent in case of heating by direct fire.

nota bene   oR is degrees Réaumur – an obsolete French scale with 0 as freezing and 80 as the boiling point of water.

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