gillmang wrote:That is very interesting. It raises a number of questions in my mind:
- to what extent is a well-conducted mash different from a wash (a mash which is filtered to remove all solids)? I always understood a wash and and mash to be different and a mash was a hallmark of bourbon production
- does furfural have a burned taste? If so this may explain the confusion of this congener with a burned mash flavour (which the old writers sometimes called "empyreumatic" - from what I can tell it means burned vegetable matter).
M'Harry (1809) indicated that simple agitation would do the trick. Also, he (or other early writers I have read) advised adding some kind of soap or fat to the still so the oiliness would preclude sticking.
On furfural: from
this site it has the aroma and flavor of caramel, maple-like, sweet. Referencing Mosciano, Gerard P&F 17, No. 4, 33, (1992). This does not correspond to "empyreumatic" which specifically refers to tails. Lee, Paterson & Piggott, Origins of Flavour in Whiskey state furfural has the flavor of marzipan.
It must be remembered that most of those old mashing protocols obtained low conversion of starches to sugars. They had relatively poor control over heating, practically non-existent temperature measuring equipment, and almost no scientific knowledge of gelatinization and saccharification.
I'd say that it was American whiskey production where distilling on the grain (ie using mash instead of wash) became dominant. The Scots had particular reasons (and problems with mash) due to the geometry of their stills. This geometry arose out of the excise tax which was based on the size of the still. So it was better to have a smaller still that ran fast. Therefore, a short boiler with a large surface area. This was very different from the Irish stills or the French brandy stills for that matter.
In spite of all that, you can end up with a nice crusty blackened layer of burnt grain on the bottom of your direct fired still and have some mighty fine whiskey. Distill off a nicely acidic whiskey/fruit wash and it'll clean right up.