When the fine DeWolf-Cosyns malts reached the US, I was puzzled by the difference between their Aromatic and Biscuit malts, both of which are about 25 degrees Lovibond in colour. After some investigation, I found that the difference was that Aromatic was high-kilned, produced like Munich malt and that Biscuit was toasted malt.
In response to a series of posts on the Homebrew Digest, I have put together the following article which describes the differences in production between pale malts (such as Pale Ale and Pilsner), high-kilned malts (such as Vienna, Munich and Aromatic) and roasted malts (such as Biscuit, Victory(TM), Chocolate, Carafa(R), Black Patent and Roasted Malt). This article will center mostly on high-kilned malts and then describe the production differences between them and the other types of malt.
There are two parts to kilning: the "drying phase" and the "curing phase." The temperature of the curing phase is what distinguishes Munich (usually about 8 Lovibond) and Aromatic (25 Lovibond), but it's the drying phase that distinguishes pale malts from "high-kilned" malts like Vienna, Munich and Aromatic [DeClerck, p.182].
For the production of high-kilned malts like Vienna, Munich and Aromatic, the initial temperature during the drying phase is higher (about 50C). Furthermore, the ventilation is considerably lower. As a result, the moisture content of the malt only drops to about 20% in the first 24 hours [DeClerck, p.197]. Typically, high-kilned malts take about twice as long to make as pale malts [Malting and Brewing Science, p.177]. Clearly there is a significant amount of enzyme loss in the production of high- kilned malts, but this higher temperature drying is important for the production of high levels of soluble sugars and amino acids which are later utilized in the production of melanoidins via Maillard reactions and Amadori rearrangements [Malting and Brewing Science, p.105]. It's these melanoidins that give high-kilned malts their colour and characteristic aroma.
Interestingly, the temperature profile of Vienna malt kilning looks more like Pilsner rather than Munich malt (from fig.79 on page 198 of DeClerck).
During the initial hot, wet heat, the malt effectively converts right in the husk. Alas, all the enzymes are denatured during this period. Because the starches in the crystal malt have been converted to sugars, crystal malts do not require mashing and can be steeped in hot water for use in extract brewing.
Biscuit and Victory are often called "toasted" malts. Really the difference between these and the much darker Chocolate and Black Patent is time and (mostly) temperature. There is some disagreement between maltsters whether damp or dry malt should be used in the roasting drum [DeClerck, p.244], but most maltsters use dry malt similar to Pilsner or Pale Ale malt. In the barrel roaster they make Biscuit, Victory(tm), Chocolate, Carafa(R), Black Patent and Roasted Malt. They also start with dry barley and make Roasted Barley and Black Barley in the roaster.
Incidentally, Aromatic malt still has enough enzymatic power to convert itself, but Biscuit has essentially no enzymes left and must therefore rely on other malts' enzymes for conversion.
Victory is a trademark of Briess Malting Co.
Carafa is a registered trademark of Mich. Weyermann GmbH.
Al Korzonas, Palos Hills, IL
Author of "Homebrewing - Volumes I and II" to be published in late fall `97 and `98 respectively.