As far as I know, no academic or other histories of porter have canvassed a 1760 book which describes in some detail the kilning of brown malt. It was by an anonymous author and published in 1760, in London. The impressive title (yet abbreviated) is The Compleat Dealer’s Assistant: Or, The Maltster’s and Mealman’s Useful Pocket Companion. The author claimed a 50 year history in the malting trade in England.
Certainly his book shows extensive experience and appears technically and historically credible in all material respects.
Other 1700s accounts exist of brown malt, e.g., by William Ellis, and Thomas Hale, but not in this detail.
In the description of brown malt, which you can read here under “Of drying Brown Malt”, The Compleat Dealer states that the “popped” form, which gets most of his attention, was one of a series of brown malts. Two other browns are also described in more summary form, these received progressively longer drying at an overall lower heat. One can infer they retained more fermentable extract, as he said brewers preferred brown malt closest to amber because, buying at the brown price, they would “run away with the profit”.
Here is a partial quotation:
Some Brewers chuse this very high blown, others in a middling way, but now (for the sake of interest) they will have it dried (if possible) as close as fine amber. I myself have blown as high as any person for chapmen in London (for making porter) in the following manner, which has given great satisfaction. The kilns are to be laid on quite thin, and when the malt has had two stirs, in about three quarters of an hour, make a large fire with good billet, well dried, slit small, and laid upon a strong iron bar across the oast hole. Let one man be employed to make up the fire, whilst two others constantly attend the kiln, to stir and keep it from burning, and relieve each other; and when your kiln has popp’d about half an hour, let the fire grow smaller and smaller till you throw off.
I read this that in the 45 minutes after the malt has been laid on, when the two stirs are done, there is no fire underneath. So that when the popping starts, it is right at the beginning. Even if that is not right, the popping phase is started much earlier than was typical of 1800s production of brown malt.
If perhaps popped brown was not the only malt for porter, it was clearly very popular, as he states he sold a lot of it to chapmen (dealers, vendors) to brew specifically for porter. He explains that this malt was placed on the kiln in a thin layer. A high fire was applied to swell the husks, i.e., as I read it again, at the beginning of the kilning and not the end as for 1800s brown malt. The popping took a half-hour, and then the fire was left to bank down for approximately two hours more. After this the malt was taken out of the kiln and would have been left to cool.
Well-dried hardwood was the fuel, which produced relatively little smoke. It is obvious some of this smoke would still get in the malt, but as other 1700s accounts make clear, porter was often long-aged in this period, which would reduce the smoke taste.
The description of brown malt production is basically similar to a number of 1800s accounts, e.g., this one by William Ford from the 1850s, except for the difference of timing when the popping was done.
The difference is significant, IMO. When newly placed on the kiln, the malt would be at its moistest. It was either moist from the maltings or in some cases wetted before being dried on the kiln, which other sources confirm. Various 1800s sources, e.g., here, suggest that the blowing or popping as it was called occurred at between 175-210 F, with the malt starting at about 90F. The lower end of that is mashing temperature. I infer the moist malt kernel would have been been caramelized with that quick initial heat, much as modern caramel malt is, to produce a viscous dark sugar.
Modern caramel malt – which is sometimes made on a kiln, not a roaster – is not diastatic: it has no enzyme content to convert starches to fermentable sugar. But it doesn’t need to be, as caramel malt doesn’t need to be mashed, or not for very long. Brown malt popped in the initial kilning stage, or blown or snapped in other usage, was probably a rough form of caramel malt. This would explain the many references in porter literature to caramel, bitter caramel, burned caramel, which gave porter its unique taste. The sugar did that but also provided, I apprehend, some converted fermentable material.
If you do the super-heating at the end of the kilning as occurred from about 1810 onwards, the barleycorns by then are much drier. While the snapping may occur, I doubt you would get any fermentable sugar production. This explains why numerous commentators of the 1800s stated brown malt wasn’t fermentable. You would still get colour contribution and some flavour. But in the 1800s, they didn’t need fermentability from brown malt. By then, it was mixed with a much larger amount of pale malt which supplied all or most of the fermentables. Black malt, newly available from 1817, would have supplied a bitter grain taste, as well.
In the 1700s, porter was still made from all-brown malt. Brown malt was always less efficient in extract than pale and amber malt since its drying at a relatively high temperature degraded part of the starch. It would have made sense to blow or pop the malt when it had the highest moisture content, to get some fermentable sugar which also contributed evidently a unique flavour to the beer.
To those who might object, that would ruin the enzyme potential straightaway, I say two things. First, good porter malt would not have needed much enzyme if it didn’t need much mashing. Second, some modern dunkel malt (German brown lager malt) finishes at 212 F and remains fully enzymatic to convert all its starches to sugar and then alcohol. Same thing with rauch malt, or smoked malt for Bamberg, Germany beer.
Finally, brewers mashed much longer for porter in the 1700s than later, including possibly the 1800s but I didn’t check this. William Ellis in the London and Country Brewer speaks of three hours in total for porter, albeit some new malt is added, the capping as it was termed. Still, that’s a long time, today most brewers can mash in one hour or half that time. The prolonged mashing assisted the low enzyme content of the malt to complete its work.
The upshot: the reversal in timing of the popping phase may be explained by the switch from all-brown malt mashing to mixed mashes benefitting from the high extract content of pale malt, and possibly as well to shorter mash times post-1800.
Some other things of note from the text: London used very little straw to kiln porter. Beer and ale in London were kilned from wood, certainly for porter, or some form of smokeless coal, e.g., culm, Welch coal, coke. Straw was available at a proper cost too far from London, in “vales” where agriculture allowed its collection from stubble.
The Compleat Dealer did admire beer made from straw-kilned malt which he called “curious”. It means, here, distinctive and high quality. But little of it was actually used to make London porter if you believe someone who started in the English malting business in 1810. I do.