Decoction Mashing
Q: I do countertop partial mashing, putting 4–5 lbs. (1.8–2.3 kg) of grain in a mesh bag and then into 5–8 quarts/liters of hot water in a beverage cooler. When my temperature is 1–2 °F (0.5 to 1 °C) low I drain a couple cups and heat it in the microwave for a minute, and then stir it back in. That usually raises the mash temperature by 1 °F (0.5 °C), and I repeat once more if necessary. I have never heard this method discussed, but it seems similar to decoction mashing. The heated liquid is not taken all the way to boiling. Is there anything wrong with this technique?
— Richard Swent • Palo Alto, California
A: I really like this approach! This is the first time I have heard of your method and cannot think of any huge problems. It is certainly similar to decoction mashing, except that you are heating the wort phase of the mash, as opposed to the grain phase of the mash. The significance of this difference has to do with where the bulk of enzymes reside, and that is in the wort phase. I want to hold that thought for a second and briefly review decoction mashing.
The decoction method begins by removing a portion of the thick mash (the heavy solids that sinks to the bottom), boiling the thick mash in a separate vessel (the “mash kettle” or “maischpfanne”), and returning the boiled portion to the rest mash (the mash that was not boiled). When the rest mash and the decoction mash are mixed, the combined mash temperature increases. Traditionally, the decoction mash method provided a reproducible way to perform step mashes. It also helped degrade cell wall bits associated with under-modified malts. There are also flavor differences attributed to the method, but the two things I want to focus on are enzymes and cell wall degradation.
As malting barley varieties and malting control have both improved over time, the norm these days is well-modified malt with more enzymes. The practical result has been a reduction in so-called mashing intensity; this translates to shorter mash times with fewer rests, and the virtual elimination of the decoction method from new brewery construction. The bottom line is that decoction mashing does not have a clear use in the production of most beers brewed on today’s global scene.
However, for traditional brewers, homebrewers, and craft brewers, decoction mashing is still relevant because certain beer styles are brewed using this method. When it is used, it is important to be careful to boil the thick portion of the mash to protect the bulk of the mash enzymes that partition into the wort phase. However, today’s malt has a much higher enzyme content than malt of yesteryear and the process is arguably more forgiving with modern malt.
So back to removing a small volume of wort from your partial mash method, microwaving it, and returning it to the rest. The only thing that you need to be aware of is that the wort phase is richer in mash enzymes than the mash trapped in your grain bag. As long as you are only removing a small portion of the total, you should have no problems. Modern malt, even “low enzyme” pale malt, can easily handle up to 25% adjunct. So there are ample enzymes for your method.
The reason I jumped so far down the decoction rabbit hole is that it is possible to use a few small bags of grain in your mash with the express purpose of having a pre-determined thick mash ready to pluck from the pot, boil, either in a small pot or in the microwave, and returning to the rest mash. I have never read anything about microwave decoction boiling and don’t know what flavor effects this method would have, but from a practical perspective it may make the process easy if you ever became concerned that you were denaturing too much enzyme by removing portions of wort, heating, and returning.
