Moisture Content in Food and Feed

Moisture content refers to the amount of water present in a material, typically expressed as a percentage of total mass. In food and feed analysis, it is one of the most fundamental compositional parameters and directly influences stability, microbial growth potential, processing behaviour, and economic value.
Water in matrices may exist as free water, adsorbed water, or chemically bound water. From an analytical perspective, moisture determination usually quantifies total volatile mass loss under defined conditions, which is operationally attributed to water. The selected method must therefore be appropriate for the matrix to avoid interference from other volatile components.

Moisture is inherent to nearly all raw materials and finished products in food and feed systems. Its level is influenced by:
‣ Agricultural conditions during crop growth and harvest
‣ Post-harvest drying efficiency
‣ Storage and transport conditions
‣ Hygroscopic behaviour of ingredients
‣ Processing steps such as pelleting, extrusion, or oil blending
In animal feed production, grains, oilseed meals, premixes, and finished compound feed are routinely monitored. In food systems, moisture is critical in nuts, cereals, flours, dairy powders, pet food, oils containing trace water, and processed products where water activity affects shelf-life.
Even small deviations from specification can alter product performance, physical integrity, or microbiological stability.

Moisture content is directly linked to microbial proliferation and product degradation. Elevated water levels increase the risk of:
‣ Mould growth and subsequent mycotoxin formation
‣ Bacterial contamination
‣ Enzymatic degradation
‣ Caking in powders and premixes
‣ Reduced storage stability
Conversely, excessively low moisture may negatively affect pellet durability, palatability, or processing efficiency. In commercial transactions involving grains and bulk feed materials, moisture also has economic implications, as payment is typically based on mass.
It is important to distinguish between moisture content and water activity (a_w). While moisture quantifies total water present, water activity reflects the availability of water for microbial growth. Both parameters may be required for comprehensive risk assessment.

Many jurisdictions specify maximum moisture limits for certain commodities to reduce spoilage and mycotoxin risk. Feed regulations may define acceptable moisture ranges to ensure product stability and prevent adulteration.
From a quality and compliance standpoint, moisture determination forms part of:
‣ Proximate analysis declarations
‣ Nutritional labelling calculations (by difference)
‣ Shelf-life validation
‣ Raw material acceptance criteria
Accurate measurement is therefore essential for both regulatory compliance and internal quality assurance.

Moisture determination is performed using controlled drying (loss on drying) methods under defined temperature and time conditions. The sample is weighed, dried to constant mass, and the percentage mass loss is attributed to moisture content.
Although conceptually straightforward, drying-based methods require strict control of:
‣ Temperature uniformity
‣ Drying time
‣ Sample particle size and homogeneity
‣ Prevention of moisture reabsorption prior to weighing
Method suitability depends on matrix characteristics. In materials containing volatile compounds other than water, drying conditions must be carefully selected to minimise analytical bias. For ISO 17025-accredited laboratories, validation includes assessment of repeatability, intermediate precision, and measurement uncertainty appropriate to each matrix category.
Proper sample preparation and environmental control remain critical to ensuring reliable results.

Routine moisture monitoring is integral to preventive quality control. In feed mills and food processing plants, it supports:
‣ Verification of drying efficiency
‣ Control of pellet conditioning
‣ Storage risk assessment
‣ Prevention of mould development
‣ Protection against economic fraud through water addition
Trend analysis over time can identify seasonal variation or equipment inefficiencies before quality failures occur. In high-risk commodities such as maize or nuts, moisture control is a primary defence against mycotoxin development.