Getting the moisture level right before storing grain is one of the most critical decisions a farmer makes after harvest. Store grain too wet and you risk spoilage, mould, and financial loss. Store it too dry and you’ve spent more on drying than necessary. Understanding the correct target moisture level for each crop is essential.
Safe moisture levels by crop
The following moisture levels are generally considered safe for long-term storage in the UK. These figures assume adequate ventilation and temperature management within the store.
Wheat and barley should be stored at or below 14.5% moisture for long-term storage, or 15% for short-term storage up to around three months. Oilseed rape requires a lower target of 9% or below due to its higher oil content, which makes it more susceptible to heating and spoilage. Oats are best stored at or below 14% moisture. Maize, which is often harvested at much higher moisture levels of 25–35%, needs to be dried down to 14% or below for safe storage.
Why does moisture level matter so much?
Moisture is the key driver of biological activity within a grain store. Above safe levels, mould spores — which are always present in harvested grain — begin to germinate and grow. This produces mycotoxins, which are toxic compounds that can make grain unsellable for human or animal consumption. At the same time, insect populations grow rapidly in warm, moist conditions, and the grain itself begins to respire, generating heat that accelerates the spoilage process further.
How is grain moisture measured?
Grain moisture is measured using a moisture meter, either a handheld probe-style device or a flow-through meter for continuous monitoring. For accuracy, it is important to take multiple readings from different parts of the heap, as moisture levels can vary significantly from the top to the bottom of a store. Many modern grain store control systems, including the Harvest Installations Store Controller, can monitor temperature and humidity conditions continuously to help you track the condition of stored grain over time.
What if my grain goes into store too wet?
If grain enters the store above the safe moisture threshold, it needs to be dried as quickly as possible. Running drying fans — with or without heat — will remove moisture over time, but the speed of drying depends on the airflow rate through the heap, ambient temperature and humidity, and the depth of grain in the store. A Maxi-Stirrer can significantly improve drying efficiency by aerating the heap, reducing compaction, and allowing more uniform airflow. Our Constant Humidity Controller ensures that heated air is only applied when conditions are right, avoiding over-drying and reducing fuel costs.
Need advice on grain moisture management?
Harvest Installations has been helping UK farmers manage grain moisture and drying since 1979. Whether you’re building a new store or looking to improve the efficiency of an existing one, our team can advise on the right equipment and approach for your situation. Get in touch to speak with one of our specialists.