💧 Moisture in food (drying)
Determination of moisture content in food by drying in laboratory oven at 103 ± 2°C to constant mass. Basic food analysis parameter.
Overview
Moisture determination by the oven drying method is the most common and cheapest method for determining water content in food. It involves drying a sample portion in a laboratory oven at 103 ± 2°C until constant mass is achieved. Mass loss is treated as water content in the sample. This is the reference method for meat and meat products (PN-ISO 1442).
Moisture is one of four basic parameters of proximate food analysis, alongside protein, fat, and ash. It is crucial for product stability — high water content promotes microbial growth, enzymatic and chemical reactions leading to food spoilage. Moisture result is required on labels of many products.
According to ISO 1442 standard, the sample (5–8 g) is mixed with dried sea sand to increase evaporation surface and prevent hard crust formation on the surface. Drying is conducted in 2-hour cycles, weighing the sample after each cycle, until the difference between consecutive weighings does not exceed 0.1% of sample mass.
In laboratory practice, alternative methods are also used: thermogravimetric moisture analyzers (e.g., Mettler Toledo HX204, Sartorius MA37), vacuum drying (for thermolabile samples), distillation methods with xylene/toluene, and Karl Fischer method (titrimetric, for low water content). Method choice depends on matrix and required accuracy.
Method principle
Gravimetric method — a sample portion (5–8 g) mixed with dried sea sand and glass rod is dried in an oven at 103 ± 2°C in 2-hour cycles. After each cycle, the sample is cooled in a desiccator to room temperature and weighed. Drying continues until constant mass is achieved (consecutive weighings differ by less than 0.1% of sample mass). Moisture is calculated: moisture [%] = (mass before drying − mass after drying) × 100 / sample mass. It is assumed that mass loss corresponds exclusively to evaporated water.
Applications
- Moisture determination in meat and meat products (PN-ISO 1442)
- Quality control of cereal products (flour, grain, bread)
- Moisture analysis of feed and feed mixtures
- Food stability and safety control
- Nutritional value declaration on labels
- Dry matter calculation and recalculation of results to dry mass
- Control of food drying and freeze-drying processes
Key parameters
| Parameter | Value |
|---|---|
| Drying temperature | 103 ± 2°C |
| Drying time | 2 h per cycle, to constant mass (6–12 h total) |
| Sample size | 5–8 g |
| Constant mass criterion | Consecutive weighing difference < 0.1% of sample mass |
| Repeatability | ±0.1–0.2% moisture |
| Weighing accuracy | 0.001 g |
Standard
- Standard number
- PN-ISO 1442:2000 (ISO 1442:2023)
- Title (PL)
- Mięso i przetwory mięsne — Oznaczanie zawartości wilgoci — Metoda referencyjna
- Title (EN)
- Meat and meat products — Determination of moisture content — Reference method
Step-by-step procedure
1. Dish preparation
Dry weighing dish with sand (3–4× sample mass) and glass rod at 103°C for 30 min. Cool in desiccator. Weigh.
2. Sample weighing
Weigh 5–8 g homogenized sample into prepared dish. Weigh with 0.001 g accuracy.
3. Mixing with sand
Thoroughly mix sample with sand using glass rod. Spread evenly on dish bottom.
4. Drying — cycle 1
Place dish (without lid) in oven at 103 ± 2°C for 2 hours. Place lid next to it.
5. Cooling and weighing
Put on lid. Transfer to desiccator. Cool 30–45 min to room temperature. Weigh with 0.001 g accuracy.
6. Drying — subsequent cycles
Repeat drying (1 h) and weighing until constant mass. Constant mass = consecutive weighing difference < 0.1% of sample mass.
7. Calculations
Moisture [%] = (m₁ − m₂) × 100 / (m₁ − m₀), where m₀ = dish mass + sand, m₁ = mass with sample before drying, m₂ = mass after drying.
8. Quality control
Perform duplicates. Difference between parallels should not exceed 0.2% moisture. Analyze CRM every series.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Laboratory oven with forced air circulation | Binder FD 56, POL-EKO SLW 32, Memmert UF 55 | 6 000–18 000 PLN |
| Analytical balance 0.1 mg | Mettler Toledo ME204, Radwag AS 220.R2 | 8 000–20 000 PLN |
| Moisture analyzer (alternative) | Mettler Toledo HX204, Sartorius MA37 | 12 000–30 000 PLN |
| Aluminum / glass weighing dishes | Al dishes Ø 90 mm with lid, pack of 50 pcs. | 150–300 PLN |
| Desiccator with silica gel | Glass desiccator Ø 200 mm + silica gel | 300–600 PLN |
| Purified and calcined sea sand | Quartz sand for analysis, pack 1 kg | 40–80 PLN |
| Glass stirring rods | Glass rods Ø 5 mm × 50 mm, set of 10 pcs. | 20–50 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Purified sea sand (calcined) | 14808-60-7 | For mixing with sample, 3–4× sample mass, calcined at 550°C |
| Indicator silica gel | 112926-00-8 | Desiccant for desiccator, with moisture indicator (blue→pink) |
Health and safety (OHS)
- Oven 103°C — burn risk. Use heat-insulated gloves.
- Hot dishes — transfer with tongs or forceps.
- Quartz sand — silica dust carcinogenic when inhaled. Avoid creating dust.
- Personal protection — lab coat, safety glasses.