Applicable to: All types of tea
Principle: Moisture is determined by weighing the tea sample before and after drying at a specific temperature until a constant mass is reached.
Equipment and Materials Required
- Sample container – clean, dry, airtight, light-resistant.
- Drying dish (Aluminum or glass) – with lid, inner diameter 75–80 mm.
- Thermostatic drying oven – temperature control at 103 °C ± 2 °C or 120 °C.
- Desiccator – containing effective desiccant.
- Analytical balance – accurate to 0.001 g.
Sample Preparation
- mix and homogenize, then store in the sample container.
Preparation of Drying Dish
- Heat the clean drying dish and lid in the oven at 103 °C ± 2 °C for 1 hour.
- Cool in a desiccator to room temperature.
- Weigh and record the mass (to 0.001 g).
Method 1 – Constant Weight Method (103 °C ± 2 °C)
(Used as the arbitration method)
- Weigh 5 g of prepared tea sample into the dried and weighed dish (accurate to 0.001 g).
- Dry in oven at 103 °C ± 2 °C for 4 hours, with lid slightly open.
- Cover the dish, remove from oven, cool in desiccator, and weigh.
- Return to oven and repeat drying for 1 hour.
- Repeat cooling and weighing until two successive weights differ by ≤ 0.005 g.
- Record the smallest weight.
Method 2 – Rapid Drying Method (120 °C)
- Weigh 5 g of tea sample into the prepared dish.
- Place in oven at 120 °C (reach temperature within 2 minutes).
- Dry for 1 hour, with lid slightly open.
- Cover, remove, cool in desiccator, and weigh.
⚠️ If results from Method 2 are not repeatable, use Method 1.
Calculation
\text{Moisture content (%) } = \frac{m_1 – m_2}{m_a} \times 100
Where:
- m₁ = mass of dish + sample before drying (g)
- m₂ = mass of dish + sample after drying (g)
- mₐ = mass of tea sample (g)
Report the average of two measurements, rounded to one decimal place, if they meet repeatability requirements.
Repeatability Requirement
The absolute difference between two test results should not exceed 5% of the arithmetic mean.