Winiarski: Improving Agricultural Food Dryers

Sometimes it’s too cloudy for solar drying and a wood-fired dehydrator can help with large scale food preservation. In 2002, Dr. Larry Winiarsk helped farmers in the wet mountainous region of Nicaragua to design and build a prototype wood fired dryer for cacao beans. The ARC publication “The Winiarski Wood Fired Agricultural Food Dryer,” details construction of a rocket-style wood-fired dehydrator.

It’s estimated that the optimal temperature for drying is between 120 and 130 degrees F. Sustained temperatures over 130 degrees can begin to cook the food. (When starting to dry foods it can be most efficient to go up to 150 to 160 F. in the initial stages of drying when lots of moisture will be evaporating out of the food.) 

A successful food dehydrator sustains these temperatures in dry air passing through food at a constant rate with even distribution for a variable period of time, depending on the food being dried. 1.) Hot air temperatures increase the rate of evaporation. 2.) Air flow through the food is equally important.

WHY?

Efficient drying moves the water inside the food into the surrounding air. Wet air cannot absorb more moisture. Hot, dry air picks up the moisture and air flow created by draft replaces moist air with dry air. In a Winiarski food dryer, air is efficiently heated and sufficient airflow of dry air through the food increases the rate of dehydration.  

The food dryer features: a) burning biomass heating air b) is relatively air tight, c) has a large chimney or fan that removes moist air and moves dry air through the food. A large chimney usually creates the draft necessary for sufficient air flow.