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The Importance of Grain Crush for Achieving Maximum Efficiency

We get a lot of questions about what is the ‘best’ crush for grain when using the Grainfather. The crush of your grain is important as the finer the grain is milled, the more efficient conversion will be in the mash. However, mill your grain too fine, and you will encounter problems in the sparge. We caught up with Dave in the UK office for some advice on what constitutes a good crush.
As all grain brewers, we understand that the purpose of the mash is to allow enzymes to work on the starch present in grains and convert that starch to sugar. This can be made easier by crushing your grain very fine. The finer the crush, the greater the mash efficiency as it is easier for the enzymes to reach and convert the starches present in the grain as gelatinisation of the starch granule can occur much faster.
100% efficiency in laboratory conditions is achieved by crushing the grains to a very fine flour, including all the husks. In contrast to this, if your grain is poorly crushed and contains a lot of husks and uncrushed grains, your efficiency will be dramatically reduced. A longer mash might help to improve this but ultimately if the enzymes are unable to work on the starch granules they will not be able to convert the starch to sugar (saccharification).
So if crushing the grains to a powder increases efficiency (and therefore reduces the amount of grain you need to use to reach your target gravity) why are brewers not crushing their grains this fine, husks and all?
Unfortunately, crushing the grain this fine extracts unwanted tannins; the bitter, astringent compound that is undesirable in a finished beer. Mashing with grain flour will also cause problems when it comes to the sparge, greatly reducing your sparge efficiency as water will not be able to run through the grain efficiently. This is where issues like a stuck sparge can occur.
So what is the ‘ideal’ crush?
Essentially you are looking to ensure that the centre of the grain (called the endosperm) is well crushed but that the husk has firstly been removed (as it’s entirely possible for this to remain in one piece) and secondly, has not been ground too small as the husks will help with sparging. It is okay to have some grain flour in your grain bill but this should be at a maximum 25% of your bill. This will enable you to reach a good compromise between maximum mash efficiency without negatively affecting the sparge or producing undesirable flavours in your beer. Below are some images of what constitutes good and bad crush.’
Poorly crushed grains
Poorly crushed grains – lots of visible whole husks
A whole husk from poorly crushed grains
A whole husk picked out from the poorly crushed grains above
Well crushed grains, endosperm is removed from kernels and well crushed
A good crush level, endosperms have been crushed and fully removed from grain husk
Finely crushed grains with a high proportion of malt flour
A very fine crush. This has a high level of malt flour and is similar to the level they would use in a commercial brewery.

For some useful information on crushing grains and mill settings this article from Brew Like a Pro is quite interesting.

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