"If the temperature gets too high the risk is that rye will form small clusters we call rye balls, typically about the size of a table tennis ball. If this happens, the outside of each rye ball cooks but the inside stays dry, and doesn't cook properly. Uncooked grain means you don't get the conversion of starches to sugars, which reduces the yield of alcohol, and, in the worst case scenario this could also affect the usual character of the spirit," says Fred Noe, master distiller, Jim Beam.
Similarly, if the cooking temperature is too low there is also a risk of uncooked rye (which again compromises the conversion of starch to sugars). Consequently, controlling the cooking temperature is vital.
"We heat the cooker using steam heated coils that circulate around the inside of the cooker. There are also additional coils through which we can run cold water, so we can easily raise or lower the temperature, and hold it exactly where we want. This is a hands on job for an experienced operator, who carefully controls the process using a computer that provides all the information, but he still has to make all the decisions," adds Fred Noe.
With the temperature sorted out, rye nevertheless poses additional challenges as it creates a viscous liquid during cooking, which can settle on the heating coils at the base of the cooker and form a sticky film.
"Cleaning the coils thoroughly is very important, otherwise the film could build up like a layer of insulation around the coils, which would reduce our ability to control the temperature," says Chris Morris, Brown-Forman's master distiller. Needless to say, without complete control over the temperature there is a possibility of the rye not cooking properly.
Cooking is followed by fermentation, when yeast is added to convert the sugars into alcohol. This stage also entails managing the fermenter (the vessel in which fermentation occurs).
"Rye produces foam during fermentation, which can rise up and flow over the sides of the fermenter. If this happens it's obviously a waste and also means having to clean up around the fermenter. To prevent this possibility we fill the fermenters lower than usual. But fermenting smaller amounts is also an inefficient use of the fermenters, and makes the production process more costly," adds Chris Morris.
Distillation produces a distinctive spirit, which then raises the question of aging and barrel selection.
"We use the same barrels for rye whiskey as for bourbon, which are unused and charred on the inside, so the spirit picks up vanilla notes during ageing. Vanilla also plays a strategic role, helping to bind all the flavours together, and balance the original character of the rye with notes derived from the cask," says Harlen Wheatley, master distiller, Buffalo Trace.
Jimmy Russell, master distiller, Wild Turkey, adds, "During the aging process rye whiskey develops more of the spicy, earthy taste, as well as vanilla, and the longer you leave it the stronger these flavours get. In our opinion rye whiskey is at its best at six to eight years. We think bourbon is best at six to twelve years. Using rye in bourbon adds body, earthiness and boldness, which balances the sweetness that corn provides, and we like this combination of flavours."
However, "Rye costs more, and is harder to use, but the pay off is that it produces whiskey that tastes really cool," says Chris Morris.
"Global interest in rye whiskey is growing, and we've really upped our capacity for making rye whiskey," says Jimmy Russell, master distiller, Wild Turkey.
Harlen Wheatley, master distiller at Buffalo Trace, concurs, "We made very little rye whiskey 20 years ago, now we can't make enough of it, with interest in rye whiskey growing significantly over the last five to ten years. It's got it's own distinct character and people want to try something different."
Rye whiskey must be distilled from a minimum of 51 per cent rye, with distillers free to choose which grains make up the balance. This includes malted barley, as it contains the enzymes required to facilitate the conversion of starches into sugars during cooking.
The mashbill (ie. recipe) for bourbon must include at least 51 per cent corn, with most bourbons also including rye and malted barley. The percentage of rye varies significantly, depending on whether the distiller wants rye to make a more upfront, or a subtler contribution, to the flavour profile.