Myth Busters: Milling and Particle Size!


The “Myth Busters” series are posts where we look at distilling lore and anecdotical industry wisdom. Is the topic at hand based on truth? On knowledge? Or is the question at hand merely a myth that needs busting?

The structure of this “Myth Buster” post is twofold. First, we’ll explain the (generally accepted) wisdom. Secondly, we’ll dive in deeper and give you the science behind it. Or at least our opinions. We’ll share as many facts as possible as well as our opinion. The goal is threefold: let’s get rid of misconceptions (1), allow you to make better informed decisions (2), in order to become a better craft distiller (3).

Anecdotical wisdom

The industry’s wisdom teaches us that distillers should prefer to mill grains to a fine flour, before mashing, because it creates a higher yield. What do you think? False or true?


A fine grain has a bigger surface are. Potentially, a bigger surface are makes it easier for water to contact the starch, that lies hidden inside the grain. In reality, this can create a faster conversion of starch to fermentable sugar, but it comes at various costs:

  1. Creating a flour, usually by applying a hammer mill, creates dust;
  2. Increased dust levels ask for more intense cleaning protocols;
  3. Dust is explosive;
  4. Dust harbors microbiological infections that float freely through your distillery;
  5. Dust is very unhealthy and can cause severe problems to the respiratory system ;
  6. Flour clumps easily, potentially infecting you wash while lowering yield.


In our experience a flour, when compared to a more coarsely roller-milled grain, does not create a higher yield of fermentable sugars. In the best case, it only converts quicker. But is a 15 to 30 minute time gain worth the associated risks of dusting the place up, putting your health at risk, and potentially infecting the wash you are working with?

We don’t think so and therefore advice you to do as brewer’s do: coarsely crack your grains, by applying a roller mill, and mash a little bit longer.

Traditional roller mill …




6 thoughts on “Myth Busters: Milling and Particle Size!

    • What I’d be more interested in is the science of ‘cracking’ the grain…
      I read discussions of 0.9mm to 1.3mm but it seems to be more a matter of opinion!
      Can you shed some more light on that?

      • Hi Elmar, I think it is a matter of opinion. If one finds a procedure that works, people tend to stick to it.

    • Hi Odin,
      Was just contemplating this – I had found this article

      Do you feel that their claims of up to a 10% increase in ethanol production when using a flour would be mitigated by a longer mash time as you suggest in your post, implying that they have considered too short a time to extract the fermentable sugars? I much prefer the idea of the coarse cracking for the reasons you suggest, but I’d have to think about leaving usable sugars in the mash. Or is there more to the picture…

      • Hi Jan, what we do is crack, not flour. With a slightly longer program and the yeast nutrient we developed we always get perfect attenuation.

  1. Hi Jan,
    I concur with Odin on this. The average distiller is using brewing processes that yield between 70 and 82 percent conversion rates. These mashing processes were designed for sweet and sour balance not for conversion efficiency. Long story short the 10% increase they claim is still below what you will gain from a quality step down mash. As you know, sweet and or sour can’t travel through the still so those processes are irrelevant and antiquated for our purposes.

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