Where Do Lava Rocks Belong in a Barbecue Grill?

by grillrepair on December 30, 2012

I found this question on ask.com but the site has changed and I do not see where to put an answer anymore.  Instead some genius (heavy sarcasm) provided what ask.com shows as the “best answer” for this question:

The lava rocks on a grill are typically placed in a single layer on top of the gas burners. This allows the rocks to collect the maximum amount of heat and spread the heat evenly on the entire surface.
That is awfully thin and leaves a lot of room for a lot of misinterpretations.  The short answer is that the lava rocks and briquettes are used instead of a simple heat shield because displace rising heat, deflect falling grease, sauces, marinades and radiate heat.  For these reasons the lava rocks (and briquettes, tiles, rods, etc.) belong supported just below the grilling grids and above the burners.  Most conduction style barbecues will have a thin grate or a heat shield designed to support the lava rocks above the burner.  The closer this support grid is to the grill grates the better effect the radiant heat coming off the lava rocks will provide.
Gas barbecues used to be called Broilers and broiler is a much better term for a gas barbecue.  Barbecue usually refers to a charcoal and wood cooker that causes flavors from the cooking process and fuel to be absorbed into the food.  A gas broiler (like electric broilers in our homes) do not crete any flavor — and usually cause a loss of flavor.  A gas broiler has a few  burners in the bottom of a fire box with heat shields (also called vaporizers, flavorizers, heat plates) mounted above the burners and a cooking grates installed above the heat shields.  Food rests on the grates and the lid is kept closed when cooking.  The way the appliance works is not dis-similar to an electric broiler (also called an oven).  With the hood closed the burners heat-up the  air trapped in the closed lid and the hot air surrounds the food for cooking.  Typically hot air will reach between 400 and 550 degrees.
This is a terribly inefficient temperature for cooking most of the meats traditionally  cooked outdoors because the food cooks too fast to absord any flavor (assuming air had a flavor!) and so slow that the meat is dripping (like sweating when surrounded by hot air) flavor onto the floor of the fire box.  Although not flavorfully exciting this is how most gas barbecues like Weber and Charbroil allow us to cook outdoors.
So a barbecue is a charcoal and wood appliance that adds flavor from charcoal and wood smoke often mixing a variety of wet and dry seasonings.  A gas barbecue is like a broiler in that the gas burners transfer heat in air trapped in the closed lid of the appliance.  A grill is  much hotter and grills tend to localize heat at the grates or cooking surface like a griddle but with open grids.
Outdoor gas appliances that utilize a layer of conductive materials like lava rocks, briquettes, porcelain rods, stainless tubes, tiles, etc. are a kind of hybrid when they are effective.  The idea is that where a typical gas barbecue uses the air trapped in the hood to transfer heat a barbecue with lava rocks will heat up and radiate heat just below cooking grates in addition to the hot air (convectional heat) surrounding the food.
There are other kinds of grills that are much more effective but the best use of lava rocks makes a lower heat barbecue capable of grilling at higher temperatures by radiating extra heat at the grate surface.
Meats that are grilled will cook faster with the outer layer sealing to force moisture to stay inside the meat.  Although barbecuing adds flavor with wood and gas barbecuing causes a loss of flavor from dripping grilling locks moisture in the meat for a natural moist flavor that is usually augmented with marinades and seasoning rubs.
Unfortunately that is not the end of the uses and positioning of lava rocks and other heat conductors.  Most of the gas barbecue brand names we are familiar with  are manufactured in Asia by manufacturing companies that are not barbecue manufacturers.  If Charmglow decided to get into the ceiling fan business they could instruct the same manufacturing plant to make them a couple different fans for sale with their brand name on the package.
This matters because anyone can look at the basic shape and primary parts of a barbecue and invent one.  They’ll make a stainless or cast aluminum box with a few burners, valves, a gas line, a layer of heat plates and cooking grates on top.  Barbecue companies that care about their products will run hundreds of tests to discover the exact size and shape of the burner, the number of ports in the burner, the exact best length and width and shape for a heat shield and the best material, thickness and design of cooking grates so the heat moves effectively and the grease is properly routed.
A manufacturer who has a recognizable brand and does not care about quality will not only use inferior materials but will stick a few burners evenly distributed with a random selection of valves, heat shields, grates, etc any place it seems to fit with no testing to see if the burners properly heat the grate area.  The only factor determining each choice is money.  These products have a lot of “hot spots” which means areas of the grid will get very hot because it is right above the burner and other areas are very cool because the heat shields are ineffective.  A few years ago a home owner could get an appliance home and determine within 20 minutes if their new gas barbecue was well designed.
Now, these retailers have gotten smarter.  They have been designing a layer of conduction not because the convectional heat is so effective that a conductive layer can create a grilling surface but because the radiating heat totally disguises the hot and cold spots of a poorly designed appliance.
Today people are so used to inefficient barbecues with lava rocks that most people no longer recognize the reason lava rocks were added to barbecues — in order to give them the ability to be grills.
In short:
a “barbecue” generally refers to a charcoal and wood appliance that adds flavor while cooking,
a “gas barbecue” is basically a convection oven that surrounds food with hot air to cook,
a “grill” makes a higher heat (usually at least 800 degrees) for searing the meats so flavors are locked in.
Gas grills like Lazyman, DCS, Lynx, Alfresco have all used briquettes and lava rocks to make their appliances  heat better and generate better effectiveness and better flavor.
Most gas barbecues we are familiar with  use lava rocks and briquettes to hide the fact that they are poorly designed.  The original question above actually gives us a clue to the type of appliance we may need to judge.  A poorly made appliance will be better served by lowering the conduction layer because dripping grease vaporizes when it hits the hot lava and rising heat spreads as it rises off the lava to the grates.  Many well-designed grills that use briquettes and lava rocks will place the conduction layer as high as possible so heat radiating from the lava is heating the food right above it.  This is not always true (DCS lava trays sat right on top of the cast iron burners) but is a good enough rule of thumb.
Majestic Grill Parts
954.247.4552 (954-2-GRILL-2)
http://www.grill-repair.com

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