Mould & Mycotoxin & Store Grain Below the Risk Line

It depends on temperature and how long you intend to store it. 14% in maize sits around 0.70–0.72 water activity — right at the threshold where common storage moulds (Aspergillus, Penicillium) begin to grow, and within a few months in warm conditions it slides into aflatoxin territory. For long-term safe storage maize should be dried to about 13.5% (roughly 0.65 aw) or below; 14% is acceptable only for short cool storage with monitoring. Enter your exact temperature and storage days to see the days-to-mould and the safe target.

Water activity is the equilibrium relative humidity of the grain divided by 100 — a measure of how much of the grain's water is actually available to fungi, on a 0–1 scale. Storage moulds do not respond to the moisture percentage as such; they respond to aw. Because oily grains hold less water than starchy ones at the same aw, 14% moisture is mould-safe in groundnut yet risky in wheat. The calculator converts your moisture to aw using each commodity's sorption isotherm, then judges risk against aw thresholds.

The most drought-tolerant xerophilic moulds (Eurotium) start near aw 0.62; the common storage moulds Aspergillus and Penicillium grow from about aw 0.70 upward, which is where visible mould, musty smells and hot-spots begin. Aflatoxin production by Aspergillus flavus needs aw of roughly 0.83 or above plus warmth (optimum 28–35°C). Ochratoxin A is cooler-tolerant and starts around aw 0.82. Keeping grain below 0.65 aw stops fungal activity for practical storage.

From a temperature- and aw-driven growth rate. The model takes a base time to visible mould at a reference condition (aw 0.75, 25°C) and accelerates it: an exponential factor for water activity above the reference, multiplied by a Q10 factor (growth roughly doubles per 10°C) for temperature. Days-to-mould = base ÷ (aw factor × temperature factor). Below about aw 0.70 the rate falls to essentially zero and the tool reports no practical growth. These are planning estimates, not guarantees.

Each commodity has a safe long-term storage moisture — about 13% for wheat, paddy and milled rice, 13.5% for maize, 12.5% for sorghum, 11% for soybean, and around 7% for groundnut because its high oil content means the same aw is reached at a much lower moisture. The calculator shows your commodity's safe moisture, the aw it corresponds to, and how many moisture points you need to remove to get there from your current reading.

Groundnut (peanut) is roughly half oil, and oil holds almost no water. So at a given water activity the grain's measured moisture percentage is far lower than in a starchy cereal. A groundnut at 10% moisture is already at high aw and severe aflatoxin risk, whereas 10% in wheat would be very dry. That is why the safe storage moisture for groundnut is around 7% — and why peanuts are one of the most aflatoxin-prone commodities in the world.

Yes, strongly. At the same moisture and aw, warmer grain moulds far faster because growth rate roughly doubles every 10°C up to the optimum, and warmth is also required for aflatoxin (optimum 28–35°C). Cool grain at a borderline moisture can be held for months, while the same grain in a hot store spoils in weeks. Cooling grain by aeration is a legitimate way to buy storage time when you cannot dry it further.

Three families: aflatoxin (Aspergillus flavus / parasiticus — the dominant risk in maize, groundnut, sorghum and rice), ochratoxin A (Aspergillus ochraceus / Penicillium verrucosum — important in coffee, barley and temperate cereals), and Fusarium toxins such as DON and zearalenone (mostly formed in the field, needing high aw, and rarely growing in a properly dry store). Each has its own aw and temperature window, shown in the reference table.

Enter your storage days and the tool compares them with the estimated days to visible mould. If the days-to-mould is comfortably longer than your storage period, the grain holds; if it is shorter, the grain will spoil first and the tool flags how big the gap is. For long-term storage you want the days-to-mould to run into many months or 'no growth', which means drying below about 0.65 aw.

No. Mycotoxins, especially aflatoxin, are heat-stable and persist long after the mould itself is killed, so once toxin has formed it cannot be reliably removed by drying, cleaning or cooking, and contaminated lots are downgraded or destroyed. The whole point of this calculator is prevention: dry to the safe moisture and keep grain cool before mould and toxin appear, because there is no cure afterward.

Equilibrium relative humidity is the relative humidity of the air in equilibrium with the grain — the humidity the inter-granular air settles to in a sealed store. It equals water activity multiplied by 100, so aw 0.65 corresponds to 65% ERH. Keeping the ERH (and therefore the aw) low is what stops mould; a store that lets damp air raise the ERH will let grain pick up moisture and begin to mould even if it started dry.

It is a planning and prevention guide, not a laboratory result. The aw conversion uses widely-cited sorption isotherm anchors and the risk classes use published growth and toxin boundaries, but real grain varies with variety, condition, damage and storage uniformity, and aflatoxin can be present from field infection before storage. Use the tool to set drying and cooling targets, and confirm suspect lots with moisture meters and accredited mycotoxin testing.

No. The calculation runs entirely in your browser using the built-in commodity sorption model and the published aw and temperature risk thresholds. Nothing you enter is sent anywhere.