There is no single safe moisture figure for all oilseeds. As a rough guide, food-grade sesame and peanut kernels are commonly specified at low to mid single-digit moisture, while castor and cottonseed often allow somewhat more.
Oilseeds hold little water because so much of the seed is oil. A moisture figure that is safe for a cereal can be too high for an oilseed. Set the limit for your product, grade, voyage and market.
Why oilseeds need lower moisture
The water in a seed sits in the non-oil part. Because oilseeds are high in oil, a small moisture figure can still mean the non-oil part is quite wet. That is why sesame at a moisture that sounds low can still go mouldy.
Moulds can produce aflatoxin, which is a major issue for peanuts. Wet seed also heats, loses quality and can develop free fatty acids, which spoil flavour and oil quality.
Typical spec ranges, for illustration only
- Sesame, natural and hulled: commonly specified at around 5 to 6% maximum or lower.
- HPS peanut kernels: commonly specified at around 7 to 8% maximum, and often lower for EU buyers.
- Mustard seed: commonly in the single digits, confirmed for your use.
- Castor seed: often a little higher, because it is crushed, not eaten.
- Cottonseed: often higher again, but it heats easily, so keep it as low as possible.
Water activity is the better guide
Moisture tells you how much water is in the seed. Water activity tells you how available that water is to moulds and bacteria. A water activity below roughly 0.7 is a commonly used guide for limiting mould growth in dry foods.
Many labs can test water activity alongside moisture. For food-grade peanuts and sesame on long voyages, ask for both. The relation between them differs by seed, so do not convert one into the other with a single rule.
Moisture changes after loading
Seed that tests well at the factory can pick up moisture at the port or in the container. Monsoon months on the west coast, roughly June to September, bring very humid air. Bags left on a damp floor, or loaded in rain, absorb water.
During the voyage, warm days and cool nights move moisture around inside the container and cause condensation. How to stop this is covered in preventing condensation and mould in oilseed containers.
How to write the moisture clause
- State the maximum moisture and the test method, for example oven drying at a stated temperature and time.
- Say when it is measured: at loading, on a sealed sample.
- Name the lab that will settle a dispute.
- Add water activity for ready-to-eat or long-voyage lots.
- Keep sealed counter-samples on both sides.
How we help
We test moisture on site and send sealed loading samples to an NABL-accredited lab. We do not load wet seed, damp bags or a container with a wet floor. Ask for a free sourcing review. For general limits, see tolerances for moisture, purity and foreign matter.