Grain is ready to mill when it is clean and its moisture is at or below 14%: a kernel should snap when bitten, and a weighed sample that loses no more than 14% of its weight on drying is dry enough. Wetter grain clogs the stones and makes flour that spoils, so dry it first; hard wheat at 12% can then be tempered by adding about 2.3 L of water to each 100 kg and resting it 12-24 hours.
Part of Community Grain Mill
The checks and preparation that make grain fit for the stones: dryness, cleanliness, and the optional tempering of hard wheat.
Wet Grain Clogs The Stones And Spoils The Flour
The carrier says grain must be dry, below 14% moisture, for clean milling, and that wet grain clogs the stones. The wiki’s grain-processing page adds that grain above 14% will mold in storage, clog equipment and give flour that spoils rapidly (Grain Processing). The grain-storage page gives safe storage levels of about 14% for up to 6 months, 13% for 6-12 months and 12% beyond a year, with maize at 13% and aflatoxin risk above 14% (Grain Storage). So 14% is the milling ceiling, and grain that has been in store should be lower.
What You Need
- A scale accurate to about 1 g, and a small tray
- A warm, dry place such as a low oven or a sunny dry table, for drying a sample
- Sieves and a winnowing space to clean the grain (Winnowing)
Method: Checking Readiness
Step 1: Bite test. Bite a kernel. A clean snap means dry; bending or squishing means damp.
Step 2: Weigh-and-dry test. Weigh 100 g of grain, dry it gently until its weight stops falling, and weigh it again. Moisture on a wet basis is (wet weight - dry weight) / wet weight. If the 100 g falls to 87 g, moisture is (100 - 87) / 100 = 13%. Say which basis you use: percentages on a dry basis read higher (Moisture Content explains why).
Step 3: Dry what is too wet. Spread grain in layers no thicker than 100-150 mm on clean, dry floors in an airy space and rake it twice a day (Grain Storage).
Step 4: Clean the grain of stones, chaff, weed seeds and soil by winnowing and screening, because a stone in the hopper chips the faces and strikes sparks.
Step 5: Temper hard wheat if wanted. The carrier suggests lightly misting hard wheat and resting it 12-24 hours so the bran toughens and the endosperm softens.
Worked Example: Tempering Arithmetic
Wheat at 12% moisture, wet basis: 100 kg holds 88 kg of dry matter. To bring it to 14% (the milling ceiling) the dry matter must be 86% of the final mass, so the final mass is 88 / 0.86 = 102.3 kg and the water to add is 102.3 - 100 = 2.3 kg, about 2.3 L. A spray of 2.3 L over 100 kg, mixed well, stays within the 14% limit; spraying more than that goes over it. Start from the measured moisture, not an assumed one: the same calculation for wheat at 13% gives 87 / 0.86 - 100 = 1.2 L.
Common Mistakes
- Tempering already-damp grain. Add water only to grain already below 14%, and measure first.
- Judging by the weather. Grain left on a floor in humid air picks up moisture; use the test.
- Feeding unclean grain. A stone in the hopper chips the faces.
Moldy grain and sparks
Do not mill grain that is moldy or smells musty: the dust is a lung hazard, and maize above 14% moisture can carry aflatoxin. Work with a damp cloth over mouth and nose, and throw out mold-damaged grain. A stone or nail in the grain makes sparks at the stones, and flour dust ignites in a cloud, so clean the grain, keep open flame out of the mill and never test for dust with a flame.
What’s Next
- Learn next: Toll Milling and Community Scheduling - who brings grain when
- Combine with: Specialty Grinds: Cornmeal, Oat Flour - moisture limits for corn and oats