Cornmeal is milled with the stones set wider than for wheat flour, from corn dried below 14% moisture, and a village that lives on corn must soak it in wood ash or lime water before milling or it will develop the niacin deficiency pellagra. Oats must be hulled before grinding and ground slowly because the kernel is oily and sticky, and since a bushel of oats weighs about 14.5 kg against 27.2 kg for wheat, a mill grinding the same mass an hour grinds nearly twice as many bushels of oats as of wheat.
Part of Community Grain Mill
Milling corn and oats on a stone mill built for wheat: how the settings change, what to do to the grain first, and how to plan in bushels when grains weigh different amounts.
Corn Needs Coarser Stones And Alkali Treatment
The corpus already advises granite for coarse corn meal and a coarser furrow pattern for corn than for wheat (Grain Mill Design, Furrow Patterns). Set the gap wider than for wheat flour (the coarse-meal gap in the mill pages is 1-2 mm) and take the grain at the carrier’s below-14% moisture, since damp corn clogs the stones; the storage page puts maize at 13% for keeping and warns of aflatoxin above 14% (Grain Storage).
The nutrition issue is separate from the milling. Corn’s niacin is bound in a form people cannot absorb, and populations that depend on corn without alkali processing develop pellagra. The wiki’s grain-processing page gives the method: boil 1 part kernels with 3 parts water, add 1 tablespoon of wood ash or slaked lime per liter of water, then rinse; the result is nixtamal, ground wet for masa or dried for grits (Grain Processing). If corn is the main grain, this step is not optional, whatever the stones do.
Corn’s germ is large and oily, so cornmeal turns rancid faster than wheat flour does (a recalled general fact, not a figure from this wiki); mill it little and often.
Oats Need Hulling And A Gentler Feed
Oats are covered by a tough hull that must be removed before grinding, or the flour is full of fibrous husk. Hulling can be done by a light pass through stones set wide, then winnowing the husks away (Winnowing). Hulls make up roughly a quarter to a third of the harvested oat by weight (recalled), so plan for 100 kg of harvested oats to give roughly 70-75 kg of groats. Heating the groats gently before milling slows the flour’s going off (a recalled practice from oat milling).
Oat flour has no gluten that makes it rise in bread, so it is baked in a mix or eaten as porridge (Porridge and Oatmeal). Its oily kernel can smear and clog the furrows, so feed slowly and brush the stones more often.
Plan In Kilograms, Not Bushels, When The Grain Changes
A bushel is a volume, so its weight depends on the grain. The standard US weights are 60 lb for wheat, 56 lb for shelled corn and 32 lb for oats (recalled): 60 x 0.4536 = 27.2 kg, 56 x 0.4536 = 25.4 kg and 32 x 0.4536 = 14.5 kg. A mill that grinds a given mass an hour grinds a different number of bushels of each. At 40 kg an hour (a planning figure only, derived in Bushels per Hour by Power Source):
- Wheat: 40 / 27.2 = 1.5 bushels an hour
- Corn: 40 / 25.4 = 1.6 bushels an hour
- Oats: 40 / 14.5 = 2.8 bushels an hour
Whether corn or oats take more or less power per kilogram than wheat has not been measured here; time a trial batch of each before scheduling.
What You Need
- Corn dried below 14% moisture, and wood ash or slaked lime for nixtamal
- A hulled, winnowed oat supply
- A mill that can be re-set between grains, and a brush to clear the stones between grains so flavors and hulls do not mix
Method: Switching The Mill To A New Grain
Step 1: Empty and brush the stones so the last grain’s meal does not carry over.
Step 2: Open the gap to the coarse setting for corn or the hulling setting for oats.
Step 3: Run a small trial and examine the meal for the texture you want.
Step 4: Close the gap in small steps until the grade is right, checking the meal temperature by hand.
Step 5: Sift and store small amounts, for 1-2 weeks’ use.
Common Mistakes
- Eating corn untreated as the main grain. Pellagra develops over months of a corn-heavy diet; treat the corn.
- Milling oats unhulled. The husk is indigestible fibre and spoils the flour.
- Scheduling by bushels. A bushel of oats is a different mass from a bushel of wheat.
Lime, ash lye and dust
Slaked lime and ash lye burn skin and eyes: wear eye protection and gloves, never splash it and rinse any contact with plenty of clean water. Corn and oat dust are explosive in a cloud like flour dust, so keep open flame out of the mill, sweep often and never test for dust with a flame.
What’s Next
- Learn next: Throughput and Operations - fitting every grain into the milling week
- Combine with: Grain Moisture and Milling Readiness - drying corn and oats before the stones