Hot stones have been used for cooking, boiling, bed warmers, and space heaters for thousands of years. A stone heated to 120° F can be the perfect hand warmer on winter campouts and hunts, and a stone heated to several hundred degrees can actually boil your drinking water and cook your food. One of my favorite rock cooking techniques is rock boiling, which can be used to disinfect water if you don’t have a metal or glass container to boil in. Rock boiling can also be used to prepare soups and teas, to create steam to open up your sinuses, and even heat up small shelters. The upside to this technique is that you don’t need any modern materials. Consider this your ultimate back-up plan, should you become separated from your normal outdoor gear and find yourself thirsty for a safe drink of water.
WARNING: Before you get started
Here’s the downside of this technique. You need to be careful. For rock boiling and any other uses of hot stones, make sure you gather the rocks from a high and dry location. Waterlogged rocks can explode violently when they heat up in a fire and send sharp stone flakes flying in all directions. The steam builds pressure in the rock causing it to blow up like a grenade. In addition to waterlogged stones, you’ll want to avoid slate, shale, quartz and obsidian as they are prone to explosion regardless of their location near or away from water. If uncertain about the types of stone you have found, toss some samples into the center of a large fire and go 50 yards away. Wait 20 minutes at that distance, watching and listening to the fire. If the rocks are going to explode, they’ll pop in the first 15 minutes. Some rocks may just crumble into sand, and these aren’t good for rock boiling either. Examine the rocks after the fire has died out, and any that remain intact are a good type of rock for boiling and heating.
Collect about two dozen egg-sized or slightly smaller stones to rock boil 2 to 4 quarts of water. Heat them in your fire for 30-45 minutes. Use sticks or split wood tongs as seen in the video to pick up the rocks and drop them into your water. Use one or two at a time, and rotate “cool” ones out and hot ones in. I’ve used wooden and bark containers, and I’ve also used holes in larger rocks to contain the stones. I’ve even dumped hot rocks in a hollowed out pumpkin at Halloween (to make pumpkin and butternut squash soup in the pumpkin shell). The kids (and adults) loved the boiling pumpkin.
Let us know if you’ve tried this method, and what you boiled or cooked. Enjoy at your own risk.