Whisky production involves a meticulous sequence of processes. The quality of each step is instrumental in creating something that far exceeds the sum of its parts. One of these is milling, the act of grinding grains to create a substrate fit for fermentation.
It seems simple, and it is, but how it’s done and to what degree affects everything.
In this article, we delve into the specifics of milling and how it influences the processes downstream. We’ll examining the tools of the trade, and the role of grist in whisky distillation.
Milling in whisky: Setting the stage for transformation
At first look, Milling is just a simple step in the preparation of grains for fermentation.
To do it, distillers use various milling techniques to obtain different granule sizes, including the use of hammer mills and roller mills. This milled grain is called grist.
The reason for doing it is also straight forward. By reducing the size of the cereal and exposing the various components, it helps with the transformation of starches into sugars, a vital process for yeast to later convert these sugars into alcohol.
So, milling is literally pulverising grains to open them up and that powder is called grist? Yes, but there’s (slightly) more to it than that however…
Let’s look at the two most common ways of milling -hammer mills or roller mills.
Hammer mills
Operation. Hammer mills employ a high-speed rotor equipped with hammers to shatter the grains into smaller pieces.
Grist Profile. Typically creates a finer grist with a higher percentage of flour.
Efficiency. Higher speed operations enable efficient milling, but can introduce higher temperatures potentially affecting the grist quality.
Roller mills
Operation. Roller mills crush the grains between a pair of rotating rollers that create a shearing action on the grains.
Grist Profile. Generally results in a coarser grist with a distinct distribution of husks, grits, and flour.
Efficiency. Slower than hammer mills but enables a more controlled grind setting preferable for extracting specific grain components.
Not all grist is the same
Grist is the output of the milling process – but it’s not just a power. It is a granular mixture that is made up of different elements, each of which with its own role to play in the subsequent stages of whisky production.
When milling for whisky, there are three main parts to it consider.
Husks. These are the outer shell of the grains. A certain amount of husks can be helpful in the filtration process when mashing, as they form a natural filter bed to separate the wort from the solids.
Grits. The coarse particles that contain a considerable portion of the endosperm, grits are a rich source of starches essential for the fermentation process.
Flour. The finest particles obtained from milling, flour contains high amounts of starches. An overabundance can lead to issues such as stuck mashes.
The balance of grist composition – grading matters
Understanding the intricate balance of grist composition is key to mastering the art of whisky production. Without the right ratio, the next stage – mashing – will either be poor, or simply not work at all.
Distillers often seek a grist ratio that optimises the extraction of fermentable sugars while maintaining a manageable process. Poweder might expose the most, but it’s tricky in other ways (heat management / filtering). They look for balance.
A common grist composition of 70% grits and fine particles, 20% husks, and 10% flour. It is a ratio that provides an optimum surface area to extract the maximum amount of sugar during mashing.
And that’s the rub of it, much of the grist ratio depends on what the distiller choses to do during mashing phase and the equipment they have at their disposal. If you have a complex modern mashtun, you have different options to someone with an old school lauter tun etc.
The ideal grist composition therefore, is not a standalone element but a reflection of a broader, integrated process. Let’s look at that a little closer…
Interplay with mashing vessel
While different mashing techniques may favour grist with higher husk content or a finer particle distribution – what’s “ideal” often comes down to vessel design.
Modern mashing vessels can be quite complex, including stirring mechanisms, water inlets and filtration systems. This all needs to be taken into consideration and needs to be compatible with the grist profile.
For example, a finely tuned grist can prevent issues such as channelling, where water finds the path of least resistance, bypassing much of the grain and resulting in suboptimal extraction.
Meanwhile, there are other elements to consider, such as the chosen mashing temperature, which influences the enzymes, gelatinisation and more. Certain conditions and ways of carrying out the mashing process might demand a very specific grist profile to make it possible to reach optimum extraction.
It’s why you can talk to some distillers who will tell you they want loads of husks, while others want none at all!
No lumps, no runaway grist spills, no clogging and good interaction with the heat and the water – milling in whisky is all about balance…
Symbiosis with fermentation conditions
Because the grist profile affects the mashing process, one must also look at it in the context of what mashing as a process is there for – preparing the input for fermentation.
Not only have they already fine tuned their grist for the mashing stage, distillers re-look at it with the next stage to see if it will be right for that part too.
For example, some distilleries will clarify their wort (the liquid that comes out of the mashtun), others will not, taking an ‘all in’ approach. Some use the mashtun to filter, but leave the fine particles flow through into the fermentation tanks…
All of this amounts to a big difference in what is ideal come the end of the mashing process – not just what works best during it. There’s good reason why producers fret over their grist composition!
Milling the ideal grist is a practice that demands a holistic perspective. It needs to be viewed not as a means to an end, nor as a precursor to the next stage alone. It’s not just about exposing more starch, nor about mashing.
Milling in whisky is the first step of a continuum where each decision reverberates down the line and throughout an entire production process.
Sure, it’s nerdy, and yes, at the end of the day it’s just broken-down grains.
But it’s the kind of detail that distillers need to get right. Because it’s at such an early stage of the process too – it’s one where a small gain build into a much bigger effect once the next steps build on it.
