Imperial malt
This was manufactured in a similar way to amber malt, but at the very end of the process oak or beech wood was added to the furnace to raise the temperature from 240 to 270º F.
Crystal malt
This was another malt finished in roasting drums rather than a standard kiln. The difference being that after germination the grains were soaked in a sugar solution or water and then roasted.
Unlike today, maltsters didn’t make multiple different shades of crystal malt. I’m sure that it did some in various colours, but this would between one maltsters product and another’s.
Its use was principally in Mild Ales and Stout. In the former, around 5% helped fill out the body. While between 5% and 25% was recommended in the latter.
Brown malt
Not left on the withering floor as long as other malt and spread in the drying kiln no more than 1.5 inches (37.5 mm) thick. Initially the heat was moderate, but when all the moisture in the malt was gone, the heat was suddenly increased by adding oak or beech wood to the fire. The sudden heat caused the grains to swell by 25%. The smoke from the wood gave the finished malt a smoky flavour.
The deliberate addition of wood to create smoke and allowing it to come into contact with the malt is very different from 18th century practice, where every attempt was made to prevent this happening. Though with the much-reduced proportion of brown malt being used in Porter and Stout - a maximum of 20% - the smoky effect would have been much less than in a beer made from 100% brown malt.
The method of making brown malt was changing, for a variety of reasons, one of which was the high risk of a fire.
"it was formerly the custom to dry brown malt also on ordinary kilns, with wire floors, but the labour on these was of a most disagreeable and exhausting character, and brown malt is now generally dried in wire cylinders."
The presence of diastase in older forms of brown malt is explained by the way it was produced. Diastase is much more sensitive to heat when moist. By first removing all the moisture from the malt at a low temperature, the diastase was not damaged as much by the finishing high heat.
Other coloured malts were produced in a very different way. To get the desired aroma in the malt, it needed to be heated to 160º F while it still had a moisture content of between 12 and 15%. If the moisture content was below 7 or 8%, the aromas would not be formed and all.
Though London brewers remained loyal to the malt behind the 19th-century Porter revolution, it was rarely present in Stouts brewed outside the capital. I have seen examples of its use in other styles, such as Mild Ale and Burton Ale, but these are relatively rare.
Black malt
Roasted like coffee and often made from inferior quality malt, though use of a better-quality malt produced a better end result. The final colour was not black, but a chocolate brown. Because it was readily absorbed water, it didn't store well.
Most breweries had adopted black malt to colour and flavour their Stouts in the second half of the 19th century. It was invented in 1817 specifically for the purpose of colouring Porter when burnt sugar was made illegal the previous year.
Some brewers mashed their black malt separately from the bulk of the mash in a small tun. The reason was simple: spent grains contained black malt fetched a much lower price than those with just pale malt. I know from Derek Prentice that this was still the case at Truman’s London brewery in the late 1960s and early 1970s.
While its use wasn’t totally restricted to Stout, black malt wasn’t very common in other styles. It does turn up in beers such as Mild or Burton Ale. Though usually both of those styles usually used a combination of crystal malt, invert sugar and caramel for colouring purposes.
Black malt gave between 60 and 70 lbs per quarter – significantly less than other malts.
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