The limestone aquifer that underlies Kentucky's Bluegrass region acts as a natural water filter removing iron salts and adding minerals, particularly magnesium and calcium. This unique sweet tasting hard water is perfect for distilling as the lack of iron and presence of calcium benefits the yeast during fermentation.
Maker’s Mark’s unique mash bill of 70% corn, 16% soft red winter wheat and 14% malted barley, the result of John Samuels baking experiment, is crucial to Maker’s Mark bourbon’s character. Corn has high starch content but doesn’t add much flavour. The winter wheat, which incidentally smells like a pampered baby when freshly ground, gives sweetness and flavour while the barley adds bolder characteristics and aids the fermentation process.
Small local cooperative farms are specially selected to supply the corn and wheat as they have the same limestone soil as the spring water used to produce Maker’s Mark. It is common for farmers in the area to plant winter wheat after the harvesting of tobacco crop to prevent soil erosion. The demand for tobacco is contracting so some of these farmers are now also starting to grow barley.
Before grain is accepted at the distillery it is checked to ensure that it is not genetically modified by testing for reactions to three different G.M. herbicides and that its moisture content is below 14%. The grains are dry cleaned to remove stems and other particles before passing through a roller mill. Maker’s Mark is thought to be unique in its use of a roller mill in the production of bourbon as opposed to the more commonplace hammer mills. The Samuels believe the hammer action heats the grain and so makes it bitter, hence their use of a roller mill.
Most bourbon distillers, including Maker’s Mark use a sour mash process. This refers to what the distillers call ‘set back’ being added to the mash. ‘Set back’ is the undistilled residue that remains from the previous distillation. The term ‘sour mash’ is a reference to this acidic, sour tasting set back.
To prepare the mash, the open cooker is filled with a mixture of limestone spring water and set back. The corn is added and a touch of what’s known as ‘pre barley’. In the words of my tour guide, Dave, “the ‘pre barley ensures there are no lumps in the gravy”. These are stirred and cooked until boiling point is reached which takes three hours. The mixture, which continues to be stirred is held at boiling point for five minutes and then dropped to 160°F. At this point the wheat is added and the mixture held at 160°F for ten minutes, before being dropped to 150°F, the temperature at which point the remainder of the malted barley is added. The mash is held at 150°F for fifteen minutes before being chilled down to between 68°F and 82°F depending on the season. The result is known as sweet mash.
Each Cyprus wooden fermentation vat holds 96,000 gallons and the bottom of this is filled with around four inches of sour mash (set back), to which 150 gallons of yeast is added. The sweet mash is then pumped in and the PH tested. More set back may then be added to adjust the PH to a level in which the yeast will thrive. Fermentation lasts three to four days. Maker’s Mark are one of the few Bourbon distillers to propagate their own yeast, made from three different strains. The fact that each fermenter produces 96,000 gallons of mash effectively dictates the size of each batch to be distilled and this yields eighteen to nineteen barrels.
Maker’s Mark, like most bourbon, is distilled twice, once in a copper column still and secondly in a copper pot still. The column still is 3ft in diameter and 37ft tall (roughly 5 stories high) with 16 plates. The use of an all-copper column helps remove sulphates. The distillate is held in a tank which is used to charge the pot stills known as doublers. These have an onion top and are heated by steam coils, and unusually for pot stills are continually fed so operate semi-continuously. The distillate leaves the first still at 60% alc./vol. and the second still at 65% alc./vol., at which point it is called ‘white dog’.
The barrels used to age Maker’s Mark are made according to strict specifications by the local Kentucky Cooperage. The oak, which is sourced from Ozarks Forest in the Appellation Mountains for its fine grain, is split and sawn into blanks that are stacked and left exposed to the elements for at least nine months to include one summer. The weathering bleaches and washes out bitter tannins in the oak and allows the development of vanillin. Many other bourbon distillers make do with just six months and no other bourbon distiller is known to stipulate a longer period than nine months.
Maker’s Mark specify that their casks are medium charred, only comprise of 32 rather than 34 staves and that these staves are 1.25 inches, slightly thicker than is usual. Unusually, they also use expensive hard walnut bungs rather than the more usual poplar bungs. These don’t swell as much during the ageing process so are consequently easier to remove to sample the barrel contents.
The white dog is diluted to 55% alc./vol. before cask filling using spring water, which has been demineralised by reverse osmosis. The legal maximum is 62.5% alc./vol. and it is believed that the 55% used by Maker’s Mark is the lowest barrel proof of any bourbon. This obviously means more barrels and rickhouses are required so is more costly but the Samuels believe a lower maturation strength gives better extraction of the sweet, flavoursome vanillin in the oak.
Maker's Mark are also the only distiller to rotate their barrels from the upper to the lower levels of the rickhouses during the ageing process. This is labour intensive but takes full advantage of the differences in temperature between the top and bottom floors of the rickhouse, which typically have six stories with three ricks (layers of barrels) per storey. After eighteen months or so, barrels that enter on the sixth storey are moved down to the first . Barrels entering on the first floor are moved to the second floor while those which start on the fourth floor are moved down to the third storey.
The top floors of the rickhouse are dry and hot and here the barrels lose water so gain a couple of percent in alcohol strength. Conversely the bottom floors are cooler and moist. On these lower levels the barrels evaporate alcohol so lose strength. Again to quote Dave the tour guide, the angels at the top of the rickhouse are hot and dry so drink water from the barrels while those in the moist cool conditions at the bottom drink alcohol to alleviate their rheumatism. The lucky angels in the middle drink a cocktail of water and alcohol from the barrels.
Unusually the Samuels’ also paint their rickhouses black to better convect the sun’s heat. Maker's Mark is aged for around 6 to 7 1/2 years, dependent on when expert tasters agree each and every barrel is ready.
Kevin Smith, the Master Distiller selects 150 casks from which the blend will be assembled using barrels from various floors of several different rickhouses. A panel of tasters check these barrels before a sample blend is made, testing against control samples to ensure the consistency of the blend’s flavour. Each 150 cask blend will fill around 3,000 cases.