How Hot Rocks Can Be Used to Make Steam

Sometimes it's easier to heat a solid object like a rock than it is to heat a container of water to boil the water for cooking or create steam for other reasons. It might be that the only available container presents a danger of melting if directly exposed to a heat source. In other cases, producing steam is the main purpose, and boiling a quantity of water to the point of evaporation cannot produce the volume required in a timely fashion.

  1. Choosing Rocks

    • As with any other substance, smaller rocks heat faster, but larger rocks will retain heat longer. If you'll be putting the rocks into a container, consider how many of them will fit. Shale, slate, and flaky rocks will not work as well as bulky, solid rocks. Sandstone may dissolve. Select rocks that do not show fractures or seams of quartz or that are at all damp, or they may explode in the process of heating or dousing. Do be sure that your rocks are really rocks and not very hard lumps of clay or other material.

    Preparing the Rocks

    • Because they will be heated above the boiling point of water, you don't need to worry too much about sanitizing the rocks, even for cooking or purifying water. Do, however, brush or wash off any obvious extraneous material that might contaminate or cloud cooking water or produce particles or gasses in the steam with unpredictable effects.

    Cooking in a Vessel

    • Bury the rocks deep in the center of a hot fire and surround them with embers. If you can get near enough to the rocks, you can test their readiness by dribbling a few drops of water on them; when it vaporizes before it has time to run off the rock, you're ready. Lift the rocks carefully, one at a time, with tongs. Lower each rock gently into the water and avoid splashing. Add rocks one at a time, until the liquid boils vigorously and steam rises in a thick cloud.

    Cooking Directly

    • A rock with a broad, flat shape that doesn't flake under the pressure of your hand can be used as a griddle or to produce small volumes of steam. Lay the rock over or in the fire, until water sizzles when dribbled onto it, then add food to be grilled or the liquid you wish to vaporize.

    For Steam in Volume

    • To fill a sauna or other enclosed space, such as a sweat lodge, with steam, rocks can be heated inside the room using a smokeless heat source, such as an electric unit for that purpose, or outside in a fire. Please note that you should not put water in an electric unit that was not intended to withstand moisture. A sweat lodge may require several rounds of bringing in hot rocks on a shovel and dousing them with water, so the fire for the rocks should be started early and kept going at a high temperature until the last round of the sweat has begun. Use the same precautions with the wood you burn, as you do with the rocks.