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Is There Any Harm Milling Twice?

TroubleShooting

Tom Volk — Blairsville, Georgia asks,
Q

I recently ordered ingredients from a well-known, online supplier. Despite specifying all grains be shipped unmilled, the base malts arrived milled, and the specialty malts unmilled. Rather than delay my brew day, I decided to proceed. I weighed out all of my grains and adjuncts and ran the whole batch through my mill. I had no problem with the mash, hit all of my target temperatures, volumes and gravities, and the batch is busy fermenting as I write. What is the impact of running base grains through a mill twice and is it wise to mill flaked barley and corn?

A
To mill once, or to mill twice? That is the question — but why shall a brewer mill at all? Brewers mill malted barley for two purposes, extract yield and husk preservation,
Response by Ashton Lewis.