The Hay Box

by Mike Forbes, from the April 2001 Newsletter

Several years ago a professor introduced me to the idea that when you cook food, much of the energy from your stove is used to overcome heat loss from your food to the kitchen air. If we can insulate our food so heat isn't lost as rapidly, then wouldn't it then take less energy to cook it?

Using rice as an example, theoretically once you boil the rice the heat energy to cook the rice completely is there. The heat leaves the rice because the food is insulated poorly, so we overcome this loss by turning the burner down low and simmering it for 30-40 minutes. Couldn't we boil the rice, remove it from the heat source and immediately put it in an insulated box where the heat energy couldn't escape and would finish cooking the rice? Yes, we could and it does work, almost. The catch is building a perfect box that no heat can escape from. I haven't been able to do it and I doubt many scientists can do it in the lab.

What I've done for the past 7 years is build various insulated boxes that do really well. I use them primarily for cooking grains like millet, groats, and quinoa and for keeping food and water warm for a LONG period of time. The trick is to build a box that has as little air in it as possible since air is a poor storage medium for heat.

I built my box to the exact size of my large cookpot. The boxes are built from rigid foam insulation with a radiant barrier (shiny aluminum coating toward the inside). I glue them together with hobby glue or foam adhesive. (Liquid Nails makes a low-toxic foam adhesive available at many hardware stores). I put little strips of wood on the inside bottom to keep the hot pots directly off the insulation.

The door is just a rectangle of foam that fits into the box. It is critical to make the door fit tightly. If you put a slight bevel to the door, it will create a much better seal. Using a table saw to make your cuts makes the process very easy and accurate. To cover the ugly shiny insulation box, I built a wood box around it and lined the door seal with flexible wood strips or duct tape.

If you build the box to your largest pot you can still use smaller pots with good success if you add more thermal mass to the box. I found that filling small pint jars with hot water from the tap works well to eliminate any air spaces in the box.

My boxes have been only 2" thick (R-14) and work very well. If I put a pot of hot food into it I can pull it out 2-4 hours later still piping hot. That makes cooking food for many people a lot easier. I would imagine that if you made the box 4" thick and sealed it really well the efficiency would be outstanding. It is my understanding that this concept is old and that traditionally hay was used in the boxes as insulation, hence the name hay box.

If you have any questions don't hesitate to email me.

Mike Forbes lives in Moscow, works in Spokane, and can't wait to be a dad in August.

 

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