Lava rocks -- which form from molten volcanic blasts -- are both friend and foe of grill users, particularly inside gas grills in which lava rocks work best as a heat distributor. Understanding the function of these rocks enhances food preparation inside grills designed for use with lava rocks. But not observing proper precautions and maintenance habits -- or using lava rocks inside grills not designed for them -- can lead to a bad grill experience.
The Oven Effect
Lava rock is lighter, less dense and more porous that most types of rock, meaning it heats up more quickly and serves as a nice distributor of heat. Using a bed of lava rock above the heat source -- such as gas burners -- of a grill promotes a sort of oven effect, absorbing the heat produced by the grill's fire source and radiating it across a larger surface area for more even cooking of food.
Gas Grill Companion
Though lava rocks technically could absorb and help distribute heat produced by charcoal or hardwood fires, they work better inside gas grills. Unlike charcoal grills, in which live coals hold their temperature for long, sustained periods, gas grills require a constant burning of a fuel stream to create heat. Lava rocks make a nice companion for gas grills because they absorb and redistribute the heat for longer periods of grilling.
Porous Shortcomings
The very feature helping lava rocks absorb and distribute heat also causes problems inside the grill when not properly maintained. Rendered fat dripping from meat inside a grill seeps into the sponge-like lava rock over time, often causing grease build-ups. At their worst, these rocks can catch fire, burning like candles or causing massive flare-ups that burn or sear meat beyond desired levels.
Maintenance and Setup
Lava rocks work best inside gas grills when spread in a single layer on a special rock grate resting above the gas jets. Spread too thickly, and the rocks don't efficiently distribute heat. Do not use lava rocks inside any gas grills not specifically designed for the rocks, and replace the rocks every couple of grilling seasons to mitigate grease buildup and fires. Using lava rocks inside grills not designed for the rocks actually reduces the efficiency of some gas burners. Turn the rocks over after every few grill uses to allow draining or burning off grease.
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