Diary of a Brewer: Mashing Methods

Now that my trial week at BrewDog is over I have returned to Saint Andrews to await word from Nikola (the brewery manager) as to whether or not I will be offered the job. In the meantime I have decided to start learning the science of brewing with the same devotion I gave my university degree. I have been taking notes from Brewing Science and Practice, a book you will note I have mentioned several times thus far in my writing. I figured the best way for me to learn from this book, considering that I have no course outline as when at university, is to document the notes that I take and transcribe them into blog posts for anyone’s interest.

So I’ll begin with a short entry detailing the different types of mashing methods used in brewing.

Mashing is the process of extracting fermentable sugars from malted grains to be converted by carbohydrate metabolism into ethyl alcohol (ethanol), carbon dioxide and heat. The enzymes that degrade the starches into fermentable sugars are effective over a wide range of temperatures, although different temperatures have different relationships between extract yield and incubation time. To maximise the extract yield while minimising the incubation time several different methods of extraction are used. Among these methods are isothermal infusion mashing, decoction mashing, double mashing and temperature-programmed infusion mashing.

1.       Isothermal Infusion Mashing –

This is the mashing method currently used by BrewDog. Coarsely ground malts are mixed with liquor      (63-67C) at a precisely controlled rate and temperature producing a thick porridge-like mash. This mash is then rested at this temperature for 30 minutes to 2 hours. The initial run-off from the mash tun is cloudy and so is re-circulated into the mash tun allowing the bed of coarse grains to filter it clear. Sparge liquor at approx. 80C is then washed through the malt during collection of the wort.

2.       Decoction Mashing –

The malts used in decoction mashing are very finely ground and are mixed with mash liquor at a relatively low temperature to create a very ‘thin’ cool mash. A portion of the mash (usually 1/3) is then removed and boiled before being returned to the original mash, thus raising its temperature. After a rest of about 30 minutes the process is repeated and the temperature is raised again. Depending on the portion of the mash that is withdrawn for boiling the process can be done in either two or three steps, known as double and triple decoction mashing. These rests at certain temperatures allow the enzymes present in the wort to degrade different types of fermentable sugars. This type of mashing, because of the finely ground nature of the malt, requires the use of a lauter tun or mash filter to remove the spent grains from the wort. This process gathers about 2% more extract from the grains than infusion mashing, and was likely employed as a mash method when stringent temperature regulation of the mash was not technically possible.

3.       Double Mashing –

This is a method favoured when there are large amounts of adjuncts (non-malt sources of extract) to be added to the mash as well as nitrogen-rich malts. The basic principal is that two mashes are prepared, one comprised of the adjuncts (as well as 5-10% of the malts) that is heated through a range of temperatures before being boiled and liquefied, while the malt is mashed at a relatively low temperature (35C) favoured by the high nitrogen content malts. After a rest period of an hour the two mashes are combined raising the temperature to about 68C. This temperature is maintained for 15-30 minutes before being raised via steam injection to 73C. Finally the finished wort is lautered to remove the small grains present due to the liquefaction of the adjunct mash.

4.       Temperature-Programmed Infusion Mashing -- 

This method of mashing is essentially a combination of isothermal infusion mashing and decoction mashing. The mash is prepared with finely ground malts (making lautering a necessary process) and is heated through a range of temperature steps similar to decoction mashing but performed by steam injection or direct heating as opposed to boiling portions of the mash. This method allows for the tightest regulation of temperatures and rest times and is favoured by many large breweries.

Obviously the range of techniques described here can all be investigated in enormous detail. I will most likely be describing these methods further in a subsequent post but for now I simply wished to make myself, and others, aware of the different methods breweries use in the production of wort through the mashing process.