Convection Oven Technique

Samples of known weight are placed in a forced convection oven for a prescribed period of time. The drying time and the temperature will vary for different materials.

ASAE Standard S352.2 (DEC92) outlines the procedure for moisture determination using a convection oven. The equipment used in the procedure is a numbered dish made of heavy gauge aluminum with a tight fitting cover, a balance with an accuracy of 0.001g, a desiccator that is airtight and contains a suitable desiccant, and a forced-draft or gravity convection oven. The oven should be well insulated, there should be uniform heating inside the oven, and the temperature should be controlled to ±0.5°C.

The aluminum dishes are dried for 1 hour at the test temperature and subsequently weighed to determine the tare weight. A 15g or larger sample of grain or seed is placed in the dish, the dish is covered and reweighed. The dish is then uncovered and placed with its cover in the oven for a heating period and temperature indicated in the table provided in the standard. For grains and seeds with moistures greater than 25%, the variability of the results can be reduced by using larger cans and 100g samples. At the completion of the heating period, the lids are placed on the cans and the cans are placed in a desiccator to cool to room temperature. They are then weighed and the moisture content is determined using one of the equations mentioned earlier.