u/CobraPuts

For those that take their grilling seriously, they know that crosshatch grill marks are a sign of uneven crust formation and a poor sear. They're scorch lines where the grate dumped heat into your meat way faster than the rest of the surface could brown. If you have strong grill marks, either those grill marks are burned or the Maillard reaction is underdeveloped on the rest of the meat surface. What we want from the grill is even browning, the kind you get on a ripping hot cast iron skillet or a dedicated sear burner with no marks at all because the entire surface sears nearly simultaneously.

But I want to talk about the physics of how to get great results from direct heat grilling, not cooking in a pan, and not using something specialized like a sear burner. When meat hits a grill, three heat transfer mechanisms contribute:

• Where you have grates, thereis conduction from the metal bars touching the meat
• Between the grates, you have radiation plus convection from the coals or heating the meat between bars.

For an even sear, we need these rates to match, otherwise you'll have dark sear marks and underdeveloped crust, or the grill grates will mask the meat from searing where they're located. Spoiler, conduction is more efficient than the other methods, so you don't have to worry about the masking effect.

Let's assume a lump charcoal bed around 700°C with emissivity ~0.85 and meat surface ~50°C (323 K):

radiant heat transfer=0.85×5.67×10−8×(9734−3234)≈42,600 W/m^2

Let's assume air temp of 400°C and h = 35 W/m²·K (natural convection with some buoyant flow)

convective heat transfer = 35×(400−50)≈12,250 W/m2

With a little analysis we can also calculate the conductive flux of the metal grates both right when meat is put on the grill and at more of a steady state.

Initial state before meat soaks heat from grates

Steady state after meat soaks heat from grates

So what are the implications?

• Aluminum will immediately singe the meat with its high conductivity.
• Cast iron produces the highest sustained flux, and will make the deepest grill marks. Not a surprise it's the ideal material for a PAN, but perhaps not for grill grates
• Stainless steel is the closest match to the radiant + convection heat transfer both in initial conditions and at steady state. For evenly cooked foods, stainless steel is your best bet, not to mention it is superior from a maintenance perspective.
• In a perfect world you would cook without any grates at all such as a rotisserie, but this is not practical for short and hot searing like you need for a steak.

So if you want a truly even sear with edge-to-edge browning instead of zebra stripes, stainless rod grates are the most justified by the physics of grilling. It's also why a thin stainless steel wire mesh grid gives such good results in many humble setups. They don't look premium, but they're conceptually sound, and combined with a hot bed of coals get out of the way of good results.

So if you're spec'ing a new grill, go for the stainless steel grates.

https://preview.redd.it/m6sprgqtofyg1.png?width=781&format=png&auto=webp&s=4a938a38f1bde65d309f8f3233a4b3f3eeef5ba3