Cumin seeds appear frequently in my kitchen. They are essential to much Indian cuisine as well as Hispanic foods. Black bean soup benefits from a healthy dose of the ground seeds and chili is positively insipid without them.
I am a proponent of using toasted cumin in heartier foods as the complexity the heat induces imparts a wonderful depth of flavor. Toasting the seeds is a bit of a trade off though, as the heat drives off or decomposes many of the essential oils that give cumin its distinctive flavor. Thus you may want to mix toasted and untoasted cumin in your preparations.
Properly toasting cumin seeds is something of a dark art. Like roasting coffee, there is a sweet spot measured in seconds to maximize the effect. Too little time and you will fail to awaken the flavor; too much and you will evoke an unpleasant bitterness. Luckily, the later is easy to determine because the seeds will take on a espresso bean color and will emit an acrid smell.
To toast the seeds, first you need a heavy skillet or sauté pan. Avoid using a non-stick pan as the high heat required can produce toxic gases. The key is to have a pan heavy enough to keep high even heat. Cast iron will work fine, but the black color can make it difficult to see the desired final color of the toasted seeds. I suspect that a more even toasting can be achieved in the oven, but the constant checking needed toward the end of the process renders its use ineffective (for me).
It is important to work in small batches. I use no more than 2 teaspoons of seeds for a 6 inch pan. The important thing is to get a single layer on seeds across the cooking surface. For most home recipes this isn’t likely to be a problem as it should be rare to need more than a tablespoon.
Finding the correct heat setting on your cook top is a little tricky, doubly so for electric ranges. To find the best setting, heat your pan on the lowest setting for several minutes then add the seeds. Cumin seeds have an amazing quality that they simply will not brown below a certain temperature, about 350°F. Once you have determined that the seeds are not browning, after about 30 to 60 seconds, increase the temperature slightly and repeat the process. Once you see the seeds begin to brown, you should be able to go straight to this cook top setting when toasting cumin seeds in the future.
Once the seeds begin to toast, they will take on a increasingly darker brown color. Toss or stir the seeds frequently. If the seeds start to jump and pop, the heat is too high so back it down. Some will say that you need the seeds to pop or crack to release the flavor. This is true if you are using the whole seeds in your dish but not so if you are grounding them.
The closer to the end you get, the more you will need to stir or toss. When the seeds take on the color of a medium roast coffee bean, you are done. Immediately dump the seeds onto a plate or sheet pan to crash the temperature.
The real trick here is determining the correct color. You are going from a brown color to a brown color so any determination is going to be largely subjective. Also if you are browning slowly, and if you are doing it correctly you will be, the mind will play tricks on you, convincing you that the color isn’t really changing. For this reason, I recommend having a small bowl of the “raw” seeds nearby while toasting for quick comparisons.
Like coffee, toasted cumin seeds will lose their potency quickly with time, so don’t toast them more than 8 hours in advance if you can help it and grind them in a spice grinder just before using.
It takes some practice to get it just right. Cumin seeds are cheap too, so it is worth it to burn a batch or two to know the site and smell. Chances are you’ll do it a couple of times without trying. Above all, be patient, it is well worth it.