01Stone, hammer or roller milling
Stone and hammer mills grind the whole kernel in one pass and give wholemeal. Roller mills break the kernel gradually over several passes, with sifting between them, so bran and germ can be separated and white flour produced.
02Number of roller passes and sifter area
More break and reduction passes and more sifting area give more white flour from each tonne of wheat, at a lower ash content. A compact plant with few passes may meet its tonnage but give a lower flour yield.
03Cleaning and tempering
Stones, dust and other seeds must go before milling, and wheat is dampened and rested before the rolls. Ask whether the scourer, destoner, magnet, dampener and tempering bins are in the price.
04Roll quality and fluting
Roll hardness, fluting profile and regrinding cost set the running cost. Ask how many hours between regrinding and whether spare rolls are included.
05Building and dust
Compact mills sit in a steel frame; larger plants need a multi-floor building. Flour dust can form explosive atmospheres, so ask what ATEX 2014/34/EU paperwork comes with the filters, elevators and motors.