Wort Boiling (1947)



by A. Slator, Ph.D., D.Sc, F.R.I.C., and J. H. St. Johnston, M.A., F.R.I.C.

Claims are sometimes made that worts boiled in fire-heated coppers produce better beers than those from steam-heated coppers.  The fire heating is said to have a greater cooking effect on the worts than steam heating, and this has an influence on the resultant beer.

The temperatures of the worts boiling in the two types of copper show some differences. Measurements made in wort boiling in a fire-heated copper showed 213°-214° F. in the upper part of the copper and 218°-219° F. in the lower part, about an inch from the surface of the copper.  In the case of a steam-heated copper (Worssam heater, steam pressure 70 Ib.), temperatures 214°-215°F. were observed throughout so long as the circulation was efficient.  The difference in temperature of the bulk of the boiling worts was therefore only slight.

Measurements of the surface temperatures showed greater differences.  These measurements were made by means of a thermo-electric couple (copper and constantan), the wire being soldered on to the metal surface of the copper at the place where it was desired to take the temperature.  The other junction was immersed in cold oil contained in a vacuum vessel.

The temperature on the inner surface of the copper in contact with the boiling wort averaged 240° F. at the bottom of the copper over the fire.  With a bright fire, temperatures 247°-252° F. were observed at this place.

Temperatures taken in a similar manner on the surface of a steam-heater gave figures 227°-231° F., which are definitely lower than the highest figures obtained on the surface of a fire-heated copper.

If there is a difference in the quality of the beer from worts boiled in these two ways it is to these differences in temperature one would look for an explanation.

A method of boiling worts by steam and at the same time getting a cooking effect by super-heating part of the wort has been devised by H. Ullmann and the Aluminium Plant and Vessel Co., Ltd. (Eng. Patent No. 498081, 3rd January, 1939; this Journ., 1939, 237).

The plant consists of a plate-type heat exchanger through which the wort is circulated by means of a centrifugal pump from the receiving vessel or copper and back again.  The wort is under pressure in the heater and the temperature is raised to the neighbourhood of 240° F.  The pressure is maintained by a throttling device at the exit of the heater and as the super-heated wort passes into the vessel the wort boils and the evaporation takes place.  In the pressure circuit is also included a vessel in which the hops can be placed and the hops extracted by means of the hot wort passing through them.  The arrangement is such that the hop extractor can be used or cut out as desired.

A small-scale plant of this type was loaned to us by the Aluminium Plant & Vessel Co., and installed in a small experimental brewery of capacity about 4½ barrels.

A comparison was made between beers brewed with the aid of the super-heater and those brewed in the usual way using the gas heated copper.  The external heater which was constructed with 36 plates holds about 13½ gallons of wort or, with the connecting pipes, about 20 gallons.  If the extractor is included another 25 gallons is introduced into the circuit, making 45 gallons in all.  The steam pressure of 40 Ib. is reduced to 11 Ib. before it enters the plates.

The wort, which is circulated at a rate of about 1 barrel per minute is under about 32 Ib. pressure and enters the heater at a temperature of 214° F. coming out at 240°-250° F. Throughout the boil therefore a proportion of the wort, 25 or 45 gallons, is at this high temperature.

It was found that by using this heater the evaporation was 20 per cent, in 2 hours and that the boiling could be carried through successfully without using heat in the copper. If the hop extractor is not used it is necessary to have the hops in a cage in the copper to prevent the hops being sucked into the connecting pipes when the wort is circulated.

A number of brews of pale ales, mild ales and strong ales were made, sometimes using the hop extractor and sometimes not.  The worts were fermented in an aluminium F.V. and then passed into a “union” consisting of one cask and a feeder.  The resultant beers were promising from the point of view of flavour, they showed a rather lower pH and rather more colour than the corresponding brews where the wort was boiled in the gas-heated copper.

It was, however, soon found that the loss in preservative value of the hops was abnormally great.  The wort boiled by means of the super-heater showed considerably less hop resin than wort boiled in an ordinary way.  This was confirmed in a striking way when a heavily hopped strong ale of O.G.1103 was brewed, the worts being boiled by means of the external heater.  The ale when about six weeks old began to develop undesirable bacteria and go off.

The method of boiling was then modified, the wort being boiled by means of super-heater for about an hour, using only a small quantity (about 1 Ib.) of hops in the extractor.  This serves to prevent troublesome fobbing, which occurs in wort boiled without hops.  After an hour’s superheating the whole of the wort was passed into the copper, the rest of the hops added and the wort boiled for another hour.  By this method there is no abnormal loss in hop resins and at the same time some superheating of the wort has taken place.  By retaining the hop extractor in the circuit a larger quantity of wort is maintained at the high temperature.

As a general result we are satisfied that the method of boiling had a favourable effect on the higher gravity beers.  Strong ales brewed in this way have a pleasing robust palate and sound keeping quality.  With lower gravity beers the effect is considerably less.  The results are of some general interest to brewers, though it does not necessarily follow that the conclusions given here apply to other types of beer.

We desire to express our thanks to the Directors of Messrs. Bass, Ratcliff & Gretton, Ltd., for permission to publish these results.

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