The best spices for summer grilling, and why each works

Every guide to grilling spices tells you what to put on the food. Almost none of them tell you what the fire then does to it. That is the interesting part, because a grill is the harshest place a spice ever goes. Steven Raichlen puts direct grilling anywhere from a medium 325 to 350 F up past an incendiary 650 F, with 450 to 600 F as the high heat most steaks and chops see, all of it measured at grate level. Modernist Cuisine draws its line where browning gives way to pyrolysis at 180 C, about 355 F, and that number is a temperature of the food, not of the fire. Your rub crosses it once the surface it is sitting on dries out. Most of what is worth knowing about grilling spices lives in the gap between those two numbers.

What the fire changes, and what it does not

Two different chemistries get muddled together here, and pulling them apart clears up most of the confusion. The first happens on the surface of the food. Maillard browning, the reaction between amino acids and reducing sugars that makes a crust taste like a crust, proceeds rapidly from around 140 to 165 C, roughly 284 to 329 F. It will not brown appreciably while the surface is wet, because water boiling off the food pins that surface near 100 C, far below the range where browning runs fast. Pat the steak dry and it browns. Crowd it and it steams. All of that is a statement about the meat, not about the Cumin sitting on it.

The second chemistry happens to the spice itself, and it is mostly subtraction. Volatile aroma compounds evaporate, which is exactly what you are smelling when the smell reaches you across the yard. Pigments break down. Whatever sugar and protein the powder contains browns, and past 180 C pyrolysis joins in. A little pyrolysis is char, which people like. Too much of it is bitter.

So a grill does not activate a spice. But be careful which half of that sentence you keep, because dry heat really does build new aroma inside a seed. Pyrazines are Maillard products, the compounds behind baked, roasted, meaty and popcorn-like smells, and they are not a myth in Cumin: substituted pyrazines are among the important aroma compounds of roasted cumin, and they are the key volatiles of a baked sunflower seed. What a grill will not do is run that reaction well. Maillard proceeds fast between 140 and 165 C, and a high direct fire is past that range and into pyrolysis before a loose grain of cumin has finished browning. That is an argument for the skillet, not for pretending the chemistry is absent. The claim that does not hold up is the other one, that fire switches on the piperine in Black pepper above some threshold. No source we can find names a temperature at which piperine turns on. Where the mechanism is real, it is named below. Where it is not, here is what the spice does, and the chemistry is left alone.

The one mechanism worth building a rub around

Here is the mechanism that does hold up, and it is the useful one. What you smell in a spice lives in its essential oil, and essential oils are lipophilic: hydrophobic volatile compounds that will not mix with water. Fat is their solvent. America's Test Kitchen ran the obvious experiment, holding crushed red pepper flakes in canola oil and in water, both at 200 F for twenty minutes. The oil pulled more than double the capsaicin of the water. Thyme treated the same way gave ten times the thymol in oil that it gave in water.

What that shows is that fat is the better solvent, not that any particular number of seconds is long enough. Take the first part. A dry powder on a dry surface stays a dry powder. The same spice stirred into warm oil dissolves, spreads across everything the oil touches, and goes into the food instead of waiting on top of it for the fire to find it first. That is the argument for blooming, and it is the argument for oil on a grill.

Smoked paprika: the grill adds nothing to it

Start here, because this is where the reasoning usually goes wrong. The smoke in Smoked paprika is not made on your grill. It is made in La Vera, in the Spanish province of Cáceres, where the peppers for pimentón de la Vera are dried by smoking, typically over oak wood, before they are ever milled. Not every paprika is smoked, and pimentón de Murcia is dried in the sun or in kilns instead. But if the jar says smoked, you are buying smoke that was put there long before you lit anything. Fire cannot add to it.

What fire does is take. The red is capsanthin and capsorubin, two carotenoids, and heat breaks them apart: a 2005 study that heated paprika oleoresin found the pigments cleaved into smaller nor-carotenoid fragments, with xylene as a byproduct. Cook smoked paprika hard and you spend the color you paid for. Stir it into oil, brush it on, keep it away from the hottest bars of the grate. If you want it louder, dust a little more over the food after it comes off. The three Spanish versions, dulce, agridulce, and picante, run mild, mildly spicy, and spicy; they differ in pungency. None of them is a smoke you make. It is only a smoke you spend.

Cumin: a dry pan does this better than a fire

Cuminaldehyde is the compound responsible for the characteristic aroma of cumin seed, a colorless oil that does not need a fire to come out of hiding. Dry heat brings it forward, and builds those roasted pyrazines besides. The usual advice is thirty to sixty seconds in a dry pan, until the seeds darken a shade and the room fills. Trust the smell rather than the clock. Then grind, then stir into oil. The grill contributes nothing here that a skillet cannot do more gently, and the skillet stops when you tell it to.

Loose ground cumin over an open flame has nowhere to go but past browning, and scorched cumin is bitter. On a grill, cumin's work is depth underneath the food's own browning, not aroma on top of it. Toast it whole, grind it, and let fat carry it in.

Black pepper: two spices in one grinder

Pepper is the most misread ingredient in any rub, because it is doing two unrelated jobs at once. The smell comes from volatile terpenes: germacrene, limonene, pinene, alpha-phellandrene, beta-caryophyllene. The characteristic pepper note itself is attributed to rotundone, a sesquiterpene the nose catches at 0.4 nanograms per litre of water. Volatile is the operative word for all of them, and once pepper is ground the aromatics evaporate quickly, which is why the advice is always to grind at the last second. The bite is a different compound entirely. Piperine makes up somewhere between 4.6 and 9.7 percent of a peppercorn by mass, melts at 130 C, decomposes rather than boiling, and barely dissolves in water at all, on the order of 40 milligrams per litre.

Read that as two instructions. Pepper in the rub stays put as bite and body, because piperine is not volatile the way the terpenes are. It is not indestructible either: light alone converts it into chavicine, isochavicine and isopiperine, which are tasteless, and how much of it comes through a hot grate intact is not a number any source we can find has measured. Pepper as an aroma has to arrive at the end, cracked coarse over the food once it is off the grate. Same grinder, two moments. Fine-ground pepper worked into a rub gives you neither: the smell has been leaving the jar since the day it was ground, and what remains is dust on a hot surface.

Coriander seed: crack it, do not grind it

Coriander seed is the counterweight to cumin, and the two together are most of the flavor of a good grill rub. Around two thirds of the seed's volatile oil is linalool, which is why crushing one between your fingers smells like lemon peel. That citrus is the first thing a fire takes and the last thing you can get back.

So keep the pieces big. Coriander cracks easily in a mortar and the coarse fragments hold their oil the way a whole peppercorn does, releasing it into the food rather than into the air above the coals. It does its best work bound into a paste with oil and lemon, or scattered over lamb and blackened carrots at the table. Ground to a powder and left over direct heat, all you keep is the woody part.

Garlic powder: the exception that proves the rule

Everything above says fat. Garlic powder says water first, and the reason is worth knowing. Allicin, the compound responsible for the aroma of fresh garlic, is not present in an intact clove at all. The enzyme alliinase builds it out of alliin the instant the tissue is damaged. Enough of that enzyme survives into the powder that one review reports complete formation of allicin in half a minute once water is added. Dry powder on dry meat has not made its flavor yet.

The other half of the problem is that garlic powder is 73 percent carbohydrate, nine points of that dietary fiber, 17 percent protein, and only 6 percent water. That is a great deal of browning feedstock and almost none of the moisture that would hold the surface temperature down. Which of those carbohydrates is a reducing sugar, and how much of that protein is free amino acid, is not something we are going to pretend to know. What can be said is that it browns early, and past 180 C pyrolysis joins in, and too much pyrolysis is bitter. Put garlic powder in a wet paste or a marinade, or hold it back and scatter it on at the end. Do not dust it dry onto something headed straight over the coals.

Dry rub, or bloom it in fat

The choice is not really about the spice. It is about the heat, and about what the food brings to the meeting.

A dry rub earns its keep when the cook is long, the heat is indirect, and the cut is fatty. Ribs, pork shoulder, a thick chicken thigh. Time lets the salt do its work, the surface dries slowly enough to brown rather than blacken, and the fat rendering out of the meat becomes the solvent those spices needed all along. A dry rub on a fatty cut is not dry for long.

Blooming in fat is the answer for everything else, which is most of what people actually grill. Shrimp, chicken breast, fish, zucchini, eggplant, corn. Lean food over direct fire has no rendering fat and no time. Warm the spices in a spoonful of oil in a pan for half a minute, off the grill, then brush that oil onto the food. You get the extraction, you get an even coat, and the spice rides inside a film of fat instead of standing on the surface waiting to be burned.

• Direct heat, under fifteen minutes, lean food: put the spice in the oil, not on the food.
• Indirect heat, long cook, fatty cut: a dry rub works, because the meat brings its own fat to dissolve it.
• Coarse survives, powder burns. Crack pepper and Coriander seed rather than grinding them to dust.
• Garlic powder wants moisture, not dry heat. Paste it, marinate it, or hold it back.
• Keep a third of the rub for the end. Aroma the fire took can be put back once the food is off it.
• The number to remember is 180 C, and it describes the food, not the fire. Below it you are only browning. Above it pyrolysis joins in, and a hot direct fire drives a dry surface past it fast.

None of this is an argument for buying better spices. It is an argument for noticing that the fire is not on their side. Sort a rub into what survives direct heat and what has to arrive afterward, and you stop feeding the best part of the jar to the coals.