Starch Conversion

Thursday May 16, 2024

It could be argued that American whiskey such as Bourbon and Rye, are among the hardest spirits there are to make, due to their grain bill they are made from. These whiskeys are predominantly made from adjuncts. Simply put, adjuncts are grains like corn (maize) and rye, with no diastatic power, which simply means that cooking them in a solution, will not result in a sugary wert or ‘mash’ that we can ferment into a distillers beer.

Distilling, has historically used the raw materials available to them at their geographical location. It stands to reason that the Scottish distillers used barley, as it’s the grain that is predominantly grown in Scotland. Likewise, Irish distillers have also used barley as it’s what was at hand locally too. When the Europeans emigrated to America, they took their knowledge of distilling with them. They soon discovered, that the native rye and corn grew in abundance, but barley wasn’t as readily available. Naturally, they began utilising the local grains. Rye was the initial grain of choice in the settlements of the East Coast but as the pioneers moved ever westward, corn became the grain of choice when they arrived in what today is known as Kentucky.

However, corn and rye differ to barley in the fact both do not malt very effectively. What these pioneering distillers discovered, was that unlike malted barley that you can just heat up and let the enzymes convert all the available starch within the grain to sugar, you have to boil adjuncts to firstly release the starch, then in turn, you add the malted barley to convert all the starch into simple sugars with yeast to produce alcohol.

So how exactly do you do this? Well, lets take a look at ‘corn mash’. First and foremost you need a supply of corn. Of late, craft distilleries have been experimenting with heritage heirloom varieties of corn, such as ‘bloody butcher’ and ‘blue corn’. Most commonly the big brand bourbons and most of the the craft bourbons distillers simply use ‘yellow dent’ field corn.

The grain needs to be dried and free from mould and any moisture, then pretty much you’re ready to go. Now the corn needs to be crushed or ground to expose the starch within the kernel. Some argue that crushed grain versus ground grain gives a different result, but at Penrock, we always use hammer milled grain, as this process reduces the kernels to almost a powder and exposes the maximum amount of starch.

Now that we have our processed grain, we need to cook it. A ratio of 2lb of corn in 1 gallon of water, should be strictly adhered to, otherwise the resulting viscosity of the ‘mash’ will be virtually unmanageable once the starch is released into suspension. A situation often comically referred to as ‘corn-crete’, but I can assure you that it’s far from a joke if the situation arises. The corn should be cooked or ‘simmered’ at or above 190ºf (88ºc) for a minimum of thirty minutes, with some distillers cooking up to two hours to ensure all the starch has been released.

It is at this stage that your ‘flavour’ grain should be added into the mix. Rye is typically the flavour grain of choice but wheat is also used as an alternative, being less spicy and offering a smoother whiskey. Pappy Van Winkle and Weller are great examples of a ‘wheated’ bourbon.

The effects on flavour with the amount of malt in the mash are debatable. It is said that the greater the percentage of malt used, the ‘softer’ the resulting whiskey. Think malt whiskey with 100% malted barley. What cannot be denied is the different effect between using rye or wheat.

Now the mash needs to be crash cooled to below 154ºf (67ºc) before the crushed or ground malted barley is added. The malted barley percentage, needs only to be small because it’s diastatic power is so good that 10% malt (by weight) will convert 90% (by weight) corn.

So once the mash is cooked at or below 154ºf (67ºc), we can add in the malt, safe in the knowledge the temperature will not denature the enzymes. To observe this process is truly a miracle of nature. For what starts out as an unconverted, fairly gelatinous mash (depending on your grain to water ratio), will instantly ‘release’ and liquify as you add the malted barley. I’m not sure who came up with this process but I can honestly say, we all owe them a debt of gratitude.

Now we have our converted mash, we can check the gravity using hydrometers. Be sure to correct for temperature variations, as the hotter the mash, the thinner it will be. As hydrometers are usually calibrated to 20ºc, we need to account for the difference in viscosity the heat has on the readings.

Many distilleries aim for an original gravity of 1.080 but others look for a lower reading. As with all things associated with distilling, everyone has their own preference and reasoning behind what they do.

One of the all consuming qualities of fermentation and distilling for me, is that there are almost infinite variations. You will never exhaust all the options and variations available to you, which can make this journey of whiskey making so endless and exciting.

Other articles about our Whiskey, Rum and Spirits

Our jounal about Whiskey, Rum and our process and how we do it the old fashioned Tennessee way

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