The mysteries of mashing

I was at Murphy and Son's, purveyors of fine finings to the brewing industry, the other week. The BFBi had organised a technical trade day and I'm always keen to keep up with my CPD. Sadly, as a Collecting Presents Day it was a bit of a flop as a biro and a bottle opener was about it. But on the plus side some of the talks were quite interesting.

In particular the talk on brewing liquor (water) treatment solved one of the mysteries of mashing that has had me perplexed for some time. Back in the day a certain town became famous for making certain types of beer using their distinctive local waters. Pale Ales made from the gypsum rich water of Burton-upon-Trent, Porters and Stouts from hard London water and pale lagers from the soft water of Pilsen are some well known examples.

Some of this I can understand. The dark grains used in stouts and porters lower the pH of the mash to an optimum level, offsetting the buffering action of the high concentration of carbonate in London water. But pilsners and pale ales? Both are made with very similar types of malt so how can very soft water and hard gypsum rich water both be ideal? The answer it seems is the different mashing techniques used. Though the malt may be similar the barley is different. Superior British barley being low in protein means a straight forward infusion mash can be used, with the malt and the liquor being mashed at around 65°C. Inferior foreign barley being high in protein traditionally had a stepped temperature decoction mash, starting at a low temperature and being raised in stages.

I'd always thought the importance of decoction mashing was the 'protein rest' stage where proteolytic enzymes can work at their optimum temperatures, but it must be important for the breakdown of starch too. Brewing liquor for infusion mashes needs to be high in calcium as the calcium stabilises the α-amylase enzyme required for starch breakdown at high temperatures. With the complex process of temperature rises it seems decoction mashing removes this need and allows our continental cousins to make pale beers with low calcium water.