It’s taken a while to get this one to work. According to the descriptions I have, Brumalt starts with a high moisture content (48%) and is well modified. After a 6-8 day germination the malt is piled up (depths vary according to descriptions) and it’s allowed to heat up to 50C in about 24 hours. After the oxygen is consumed and enough carbon dioxide accumulates it eventually cools down with the whole process taking about 30-40 hours. According to Briggs “Under these conditions rootlet growth ceased, the starchy endosperm became pulpy and the sugars and amino acids accumulated…” The malt is then dried at 65 C and kilned (or cured) at less than 100 C or 212F producing a dark malt at 15-30 or even 40 EBC units and yields a “sugar and melanoidin-rich malt when mashed”
Now this is the tricky part for the small scale home maltster but I’ve recently discovered that the amount of malt used vs. the container size is very important, otherwise you may not reach 50C or it may take a long time, like 3 days. I’ve tried different amounts for different lengths of time in different coolers and containers and I’ve found that 10 lbs in a 5 gallon cooler works perfectly. The cooler mimics the conditions of a larger pile of malt.
Interestingly this technique is mentioned in the London and Country Brewer of 1736 in Chapter 2. “Now when it is at this degree and fit for the Kiln, it is often practised to put it into a Heap and let it lye twelve Hours before it is turned, to heat and mellow, which will much improve the Malt if it is done with moderation, and after that time it must be turned every six Hours during twenty four; but if it is overheated, it will become like Grease and be spoiled, or at least cause the Drink to be unwholsome” Also in this text is this description of the malt near the end of germination: “and when it is fixed and the Root begins to be dead, then it must be thickened again and carefully kept often turned and work’d, that the growing of the Root may not revive,” This quote describes the withering of the roots which is more evident with traditional longer germinations. Purposely withering the malt on the floor was also a common practice when floor malting and this was done by spreading out the malt to a very thin layer of 1 or 2 inches. Just for fun I thought I’d try drying out the malt a little by spreading it out to see if using a somewhat dryer malt had an effect on this process. I was thinking that this hot couching process might be the way to add more colour to my diastatic brown malt. Unfortunately, when the malt has undergone a long traditional germination or has been withered the moisture content will be lower, 27% in my case. I believe that with a lower moisture content the proteolytic enzymes are not as effective as a malt with a higher moisture content when the temperature rises.
I’ve created dark malts before by stewing the malt in my kiln at 50C immediately after germination. 16 hours of stewing seems like the magic number and then drying and kilning as you would for a pale malt. But I wanted to see if I could get a very dark malt naturally with this hot couching method instead of stewing it in my kiln. The second batch uses the same Skagit Valley barley as the first one given to me by Skagit Valley Malting. Both started with a 46% moisture content using 8 hour steeps and 8-12 hour rests. Both were well modified with acrospires reaching the full length of the grain having germinated at roughly the same temperature. The only difference is that the first batch withered for 28 hours before being put in the cooler. To wither I simply spread it out to an inch depth on window screens with space under the screens for air-flow. After withering it had a moisture content of 27.5% whereas the un-withered batch had a moisture content of 40%.
The first batch reached 51 C, its maximum temperature, after 32 hours in the cooler. The malt was covered loosely with dish towels for insulation but allows for some oxygen. (I’ve tried it with an airtight lid but it doesn’t work) I then let it cool down for another 16 hours, for 48 hours total. When I took it out the temperature was at 47 C. It then went in the kiln to dry at 65 C (air on temp). The second batch went into the cooler at 40% moisture having gone through the same germination regime minus the wilting. It was a little faster and reached 51C right around 24 hours, just like the textbook says! I then let it cool down to 45 C for a total of 39 hours in the cooler. This malt was then dried for 12 hours under 50C which also makes a difference due to the fact that the enzymes are still active during this time especially at the beginning.
There’s huge difference in colour due to the difference in moisture content at this “hot couch” stewing phase. Not only are the enzymes more effective with more moisture but continue their activity during the longer drying phase after the “hot couch”. Perhaps if a traditional floor malt was not as dry as my “wilted” malt that this method played a role in adding colour to the diastatic brown malt of the past.
Malt # 1 Withered Malt # 2 Not Withered
- 46% moisture Same
- 5 day germination acros. full length Same
- Withered 1 ” depth on screens 28 hours
- 27.5 % moisture content
- In cooler 48 hours max temp 51 C In cooler for 39 hours max. temp. 51 C
- 4 hours drying at 65 C (air on temp) 12 hours drying (malt temp. 40-50C)
- 4 hours at 205 F 3 hours 65 C (Air on temp) 55 malt temp.
- Not much colour (even after another 3 hours at 200F) . 4 hours 200F (malt temp max 168)
- 3 hours 200F on shallow pan (malt temp 200)