Decoction mashing: conventional and unconventional applications of a historic technique
As mentioned in last month’s blog, I have a fascination with brewing techniques that have been fading from use for decades, and that many brewers would consider historic or archaic.
Usually time-consuming, technically demanding, and requiring specialised equipment, traditional practices such as decoction mashing, top cropping yeast, and cask ale have faded from use in modern brewing in favour of techniques that are more time and resource efficient, and less dependent on the vagaries of individual human skill and experience. \
The reason that archaic brewing methods survive at all is not because of their efficiency or utility, and never solely for the cultural significance of the tradition itself, but because old ways of brewing uniquely shape the way beer looks, tastes, smells, and feels in ways that are not replicable by modern methods. They are methods of brewing that are better understood by their impact on flavour and culture, rather than in columns on a balance sheet.
Let’s have a look at decoction mashing. In brewing parlance, ‘mashing’ is the process of combining water, crushed grain, and heat to create a porridge-like mash. With sufficient hydration, various enzymes that form during the germination of malted grains switch on within specific temperature ranges and act as catalysts for the reduction of big, complex proteins into medium-weight proteins and amino acids, and long-chain carbohydrates (starches) into sugars. By controlling temperature, pH, time, and cofactors such as the concentration of particular mineral ions in the water, brewers can exert a great deal of control over the mashing process so that the sweet liquid produced - called ‘wort’ - will ferment into beer that meets specifications for alcohol content, flavour, texture, and appearance.
A simple, effective, and widely used mashing technique is called ’step infusion’, where mashing takes place in a single vessel with a series of short rests at progressively increasing temperatures. Mashing might start at 63ºC for a 20 minute rest, with heat then applied to bring the mash up to 72ºC for a 10 minute rest, then heated again to 76ºC to reduce viscosity and denature most of the enzymes. This process will typically take 60-90 minutes and is very simple to plan and execute, even for new products.
Decoction mashing is different. Two vessels are required. Mashing starts in the mash tun, and then the thickest third of the mash is drawn off into a secondary vessel called a decoction kettle. There, it is stirred and heated, with one or two rests at various temperatures before being boiled for anywhere from 10 to 40 minutes. While the decoction is being boiled, something special happens. Maillard reactions between amino acids and sugars form melanoidin compounds that intensify malty-bready flavours, and darken the colour of the wort. This is the same chemical process that creates a flavoursome crust on bread and, while the mash is boiling, an aroma similar to baking bread noticeably intensifies. Immediately after boiling, the decoction is returned to main mash, raising the temperature and activating different enzymes. This process can be repeated two or three times, depending on how many temperature steps are required. The time involved in drawing, heating, and boiling multiple decoctions means that a decoction mash can take hours longer than a step-infusion mash.
Decoction mashing was developed hundreds of years ago in Central Europe as a way of getting predictable results with no thermometers, and to get the most out of the local malted barley, which was traditionally made with a shorter germination time that necessitated more processing in the brewery. Despite the presence of thermometers in breweries today and the availability of modern malts that don’t require special treatment, decoction mashing is still widely used in Southern Germany, and is a legal requirement for traditional beers in Czechia. While there is certainly great reverence for tradition, these decisions are also about flavour: the rich aroma coming off the boiling mash that carries through into the final product, adding something more without making the beer heavier or hard to drink in a session.
Long Time Lager is our original, flagship product for decoction mashing. The mashing process builds flavour and colour above and beyond what would otherwise be provided by the single type of malted barley this beer is made from. I recently switched from using a conventionally grown ‘under-modified’ pilsner malt with similar specs to the original malts used for decoction in Central Europe, to a fully-modified pilsner malt that’s also certified organic and regenerative. The reason for the change is to improve head retention and foam quality on the beer, and I just couldn’t seem to get there with the under-modified malt, no matter where I tweaked the process. The next batch of Long Time with the new organic malt is in tank now and is coming together nicely, but it’s too soon yet to properly assess the impact of the change. It’s just starting cold maturation and should be on tap by late July.
Given its history, decoction mashing is almost exclusively associated with Central European-style lagers. Naturally, that led me to wonder what would happen if the technique were used to make other kinds of beer. What other beer styles demand a malt presence broad enough to balance high hopping rates without being loud or overbearing, can benefit from a touch of extra colour, and need a crisp, bright finish? Hello, decoction IPA. I wonder where else this question might lead us?
We’ve got a Double IPA on tap at the moment (had cans, but they sold out) called ‘Beyond the Coast’, and it underwent a double decoction mash. I wrote a bit about it in last month’s edition so won’t cover old ground except to reiterate that it’s a belter - the colour and malt presence are heavily influenced by the maillard reactions in the decoction boils and, at 8.5%, it’s the biggest beer we’ve made so far.
Given my vintage, I wistfully remember the IPAs of the 2000s and 2010s: generally maltier and a little darker in colour, and way more bitter, with hops that leant more into pine and citrus rather than tropical fruit. The crystal malts that were used for caramel flavour and deeper colour could sometimes be an issue: consumed fresh, these beers could be wonderfully balanced gold-amber glasses of caramel/toffee, resinous, citrusy, bitter goodness, but age would morph those pleasant malty notes into overly sweet, papery oxidised flavours that masked the hops. As a response to this issue, IPA recipes reduced or dropped crystal malts entirely, making the next generation of IPAs leaner and paler. I like Beyond the Coast, because decoction has recreated some similar flavours and darker colour of the circa-2010 IPAs with a lower risk of instability and rapid oxidation. We’ll definitely be doing more IPAs and potentially other beers with decoction down the track.
