The New York Times archive has also has been digitized. Searching under "Bourbon Whisky" (the NYT of the era preferred to spell whiskey without the vowel), I found what seems an important key-hole to perceive how Bourbon was manufactured in Kentucky in the era mentioned.
The article is called "Kentucky Whisky: The Different Methods of Distillation, The Process Described" and appeared in the April 4, 1870 issue.
The article was however a reprint of one from the March 14, 1870 Louisville Commercial. The article is quite short but manages to describe six contemporary forms of whiskey manufacture, which are called "grades" in the article.
The six types are: "sour mash, pure copper", "sour mash, log and copper", "sweet mash, pure copper", "steam copper", "Bourbon steam", and "High Wines". Details of mashing are given too.
The first method was double pot distillation over a fire, the mashing using slop in a multi-day process. Interesting detail is given e.g., it is mentioned either yeast was added to the mash to ferment it, or a portion of fermenting mash was added which sounds akin somewhat to the krausening process in brewing.
The second method was (apparently just) one run through a beer still made of wood and copper - rum is still made in such a still in Guyana today. The third was like the first except using water no slops and the mashing completed in a day. The fourth seemed to use an all-metal column still, the fifth was a method described as used only in Bourbon County, Kentucky and similar to the last except the output of the still was doubled in a doubler. The Bourbon steam method sounds like the way Bourbon is made today except the doubler used then was wooden. High wines was similar to Bourbon steam except barreled at distilling-out proof (presumably relatively high - no dilution with water prior to barreling) and made from lesser quality grains. Also - an important indicator in my view - High Wines was barreled in "unburnt" barrels, the implication being the first five processes all used charred barrels for aging.
The last form sounds like a high proof grain whisky in modern terms.
The other forms vary by being made either in pot or column stills, using sour or sweet mash, and whether and how the singlings from columns were re-distilled. It was said that some distillers departed from these 6 modes but most did not because it would change the accepted taste.
While describing 1870 methods, in a sense the article is a picture of the processes used over the 1800's, since double pot distillation would have been the earliest method and Bourbon steam is where things ended up more or less to this day. In 1870, numerous processes were being used, spanning original and latest technologies, whereas today bourbon is made largely only in one type of still and is always re-distilled.
Microdistillers seeking inspiration from early methods might take note.
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