Interactive lesson

Drying grain, step by step

Interactive lesson: how much moisture grain may hold, how to measure it without a laboratory, how to dry it on a tarpaulin, in a crib and in a dryer, and how to prevent mycotoxins.

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The whole lesson as text

1. Why moisture decides everything

Grain is alive: it breathes, uses up starch and gives off water and heat.

Grain breathes — The damper and warmer it is, the faster it breathes. Above 14–15 % moisture at summer temperatures, grain heats up by itself.
The limit for storing — Wheat, rye and maize for storing up to a year: 13–14 % moisture. Dry beans and field beans: 13–14 %.
Seed is stricter — For long storage and for seed, grain and maize need 12–13 %, beans and field beans 11–12 %.
The damper, the more urgent — Grain at 25 % moisture and 25 °C can go mouldy in two or three days, at 16 % in two or three weeks. In the UK and Ireland grain often comes off the field at 16–20 %, so start drying within 24–48 hours of harvest.

Why: Grain that goes into a sack at 18 % moisture heats up within two weeks and smells of mould. Moulds produce mycotoxins, poisons you can't see and that even cooking doesn't destroy. Below 13 % moisture and below 15 °C (59 °F) grain is almost dormant and keeps for years.

Barley and oats need 13 % for keeping up to a year, 12 % for long storage.
Maize on the cob dries in the crib through to spring, and seed cobs are kept separately.

2. Measuring moisture

Without measuring you're only guessing.

Grain moisture meter — The most accurate, ± 0.5–1 %. Set it for the type of grain and check it once a year.
Oven and scale — Weigh exactly 100 g of grain in a shallow dish. Oven at 100–105 °C (212–220 °F), dish on the middle shelf, 3 hours.
Weighing and the sum — Cool the sample in a closed jar and weigh it. Repeat hourly until the weight stops changing. 86 g left means 14 % moisture; allow half a percent of margin.
The salt test — Fill a jar a third full with grain, add 2–3 tablespoons of dry salt, shake for a minute and leave for 15 minutes. If the salt sticks to the glass, the grain has more than 15 % moisture.

Why: On a small field there are four ways: a moisture meter, the oven, the salt test, and teeth or a hammer. Each is good enough to decide whether to keep drying the grain or to store it.

Take the sample from several places in the sack or heap, not just the surface.
Dry wheat and maize crack between the teeth rather than squash. That's only a supporting sign.