Use of a Microwave for Dry Matter Determination

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Use of a Microwave Oven to Measure Dry Matter of Wet Feeds

Dr. Karen L. Jacobsen,,   USA cell:  706-340-0999 


  1. Collect a representative sample of the feed by taking several handfuls at random sites, mixing them, and removing a sample.
  2. Place this sample on a paper plate and spread in a thin layer.
  3. Use a small scale that has a maximum capacity of 200-400 g (ideally accurate to +/- 0.1g)
  4. Either tare the scale back to zero or record the weight of the paper plate.
  5. Accurately weigh 100 grams of the feed. This is the wet weight.
  6. Place a glass of water in the back corner of the microwave (3/4 full).
  7. Repeatedly microwave the feed on the paper plate on high for 2-3 minutes each time, stirring the sample in between heatings. A paper towel under the plate can be used to absorb moisture.  Discard the paper towel as the feed becomes almost dry.  Decrease time to 1 minute, then 30 seconds as feed becomes almost completely dry.
  8. When the feed feels completely dry, weigh and record weight.
  9. Then heat again for 30 seconds each time until the drying does not reduce the weight. If any charring occurs, use the previous weight for calculations. This is the dry weight.
  10. To calculate the percent dry matter, divide by the dry weight by the wet weight and multiply by 100.


wet weight = 100 grams

dry weight = 35 grams

35/100 = .35 x 100 = 35%