Measuring moisture in organic materials such as biomass, wood, grain, seeds, meals and agricultural by-products is a crucial step in industrial processes. Moisture directly affects thermal yield, durability, density, weight, final product quality and even operational safety. Yet one factor is often overlooked in day-to-day operations: the impact of low ambient temperatures on the measurement itself.
Especially in cold climates, or in unheated areas such as drying yards, unheated steel silos or outdoor conveyor lines, low temperatures can significantly distort moisture readings and, as a result, compromise operational, commercial and energy decisions.
In this article we look at the physical and technical effects of cold on the main moisture measurement methods, with data, references and ways to mitigate them.
Hygroscopic behavior in cold environments
Organic materials are hygroscopic by nature: they constantly exchange moisture with the air depending on relative humidity (RH%) and temperature. The relationship between the two is described by the sorption isotherm, which shows how the same material can reach different equilibrium moisture contents at different temperatures.
As a rule of thumb, for every 10 °C drop in ambient temperature at constant relative humidity, the equilibrium moisture content of products such as wood and grain rises by 0.5 to 1.2 percentage points.
Example: dry wood in equilibrium at 12% moisture will drift toward about 13% if it stays long enough in an environment 10 °C colder at the same relative humidity. Very wet materials, such as fresh chips above 30%, are above the fiber saturation point and are hardly affected.
Main technical effects of low temperatures on moisture measurement
1. Changes in dielectric properties
Most industrial moisture meters, especially instant-reading ones, rely on the dielectric constant (relative permittivity) of the material. Water has a very high value (~80 at 20 °C), while dry materials are much lower (between 2 and 10). That contrast makes accurate moisture detection possible.
However, dielectric properties change with temperature. The dielectric constant of liquid water actually rises in the cold (from about 80 at 20 °C to about 88 at 0 °C), but the mobility of bound water and the material’s electrical conductivity drop, and the net effect depends on the material and the sensor frequency. In practice, with cold grain and biomass, meters without temperature compensation usually read lower than the true moisture. Below 0 °C the error is much larger: ice has a dielectric constant of about 3, so frozen water is practically “invisible” to the sensor.
📌 Reference: Ellison, Lamkaouchi and Moreau (1996), Water: a dielectric reference, Journal of Molecular Liquids.
2. Condensation and surface moisture
In cold, humid environments, condensation can build up on the material’s surface, especially when it moves between temperatures, such as during transport or when samples are taken into heated rooms. This free water on the surface of the kernel or particle can make the measured moisture read high by several percentage points.
Condensation can also interfere with capacitive, resistive and microwave sensors, because it creates a temporary, highly conductive layer that does not reflect the material’s true internal moisture.
📌 Reference method for grain (oven): ASABE S352.2, Moisture Measurement — Unground Grain and Seeds.
3. Physical changes in the material: freezing and slower diffusion
At or below 0 °C, water in the cell structure can freeze. This changes how internal moisture diffuses to the surface and makes measurement harder for thermal (loss-on-drying), dielectric and even infrared methods.
Moisture diffusion is also much slower at low temperatures: in materials such as wood or soybean meal, it can be several times slower at 5 °C than at 25 °C.
The result is longer response times, inconsistent readings and underestimated total moisture, particularly in quick tests.
4. Changes in bulk density and flow
Thermal contraction of organic materials is tiny and barely changes their density. The real cold-weather effect comes from water: below 0 °C, moisture between particles can freeze into lumps, changing how the material packs and altering its bulk density and flow on conveyors and in silos. That affects sensors that relate moisture to weight, volume or density, creating indirect reading errors.
📌 Tip: for biomass stored outdoors in winter, check for ice or frost in the load before using density readings to estimate moisture or energy.
Direct industrial impacts
🔥 Biomass for boilers
Moisture directly affects the net calorific value (NCV) of biomass. For every 10 percentage points of extra moisture, NCV drops by roughly 15 to 20%, so more material is needed for the same energy. Cold-induced reading errors can let wet biomass slip through unnoticed, raising transport, storage and combustion costs.
🌲 Dried and sawn lumber
Wood drying depends on strict moisture control. In cold environments, uncompensated sensors can cause reading errors that lead to over-drying (cracks and distortion) or under-drying (mold and rejected product). See also how cold weather affects wood drying.
🌾 Grain, seeds and feed
Measurement errors at low temperatures can produce false “on target” readings, leading to wet grain going into storage. That encourages mold, mycotoxins and loss of nutritional value. In grain trading, a 1% difference in moisture also means considerable financial losses at the final weigh-in.
Best practices to offset the effects of cold
- Use meters with automatic temperature compensation, which adjust readings to ambient or sample temperature.
- Sample after acclimatization, letting the material reach thermal equilibrium with the measuring environment (15 to 30 minutes).
- Monitor temperature and moisture together, with real-time logging.
- Avoid condensation by keeping sensors in a dry place, protected from sudden temperature changes.
- Recalibrate sensors periodically, especially in regions with large seasonal temperature swings.
Conclusion
The influence of low temperatures on moisture measurement is a critical factor that often goes unnoticed, but it can have significant technical and economic consequences for industrial processes that handle organic materials. From quality-control distortions to boiler problems, reading accuracy has to be ensured even in adverse conditions.
Companies working with biomass, wood, grain, seeds, feed and related products should factor this into their planning, especially in cold regions or outdoor processes.
Marrari Automação develops dedicated solutions for accurate moisture, volume and density measurement in organic materials, with rugged technology, temperature compensation and industrial reliability for a wide range of environmental conditions.
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