Why does spicy food get spicier when heated in a microwave oven?

Or am I just imagining it? I’m perplexed.

I think you are imagining it.

Perhaps this will help . . .

My favorite bar-b-que sauce has a sentence written on the lable that says “heat sauce to double flavor”.

Maybe it isn’t specifically the microwave, maybe it is just that heating food brings out spices in general.

My WAG.

WAG

Many/most of the active components of a spice compound are held in oil and/or water based solutions of some kind and will tend to release airborne components when heated which can intensify the experience of “spiciness”. A microwave oven’s action of heating by generating heat within the food mainly via the water molecules in the food being heated would release these spice compounds quite efficiently.

I might also guess that microwaved food might (on average) be eaten “hotter” (temp wise) than oven cooked foods which generally have a somewhat longer cool down period in order to handle the serving dish which heats up less in microwave cooking, which would tend to enhance the “spicy” aspect of the food… ie steaming hot chili tastes “spicier” (to me at least) than more tepid chili.

So microwaving probably doesn’t really make the food any spicer but the rate at which the food is heated and the way it is served out of a microwave (ie hotter) probably makes it “seem” spicier heat and aroma wise.

Here’s my two cents…

I just LOVE hot (spicy) foods. I make my own picante sauce on occasion. When I make it, of course, I have to eat some right away. It is usually quite hot (spicy). Whatever I don’t eat on the first day, I refrigerate to eat the next day. When I eat my concoction the next day, it is noticeably hotter (spicier). I don’t think it was the refrigeration that did it. I think it was time. I’ve noticed the same phenomenon with other spicy foods that were eaten as leftovers the next day (I assume you are eating leftovers if you are microwaving the food, and saying it is “spicier”, suggesting that it is spicier than the day before).

If you really want to know which it is (time or microwave heating), you can do an experiment. Make a spicy dish one day, and divide it into two portions. Heat one in the microwave, and the other in a conventional oven. Taste both, and compare them for spiciness. Save a portion over night, and do the same as before with the heating with the two different types of ovens. Compare them to each other, and also compare their spiciness to the dishes from the day before. I know that comparing today’s spiciness to yesterday’s remembered spiciness is subjective, but from my experience, the difference can be huge, and very noticeable.

For dishes made from peppers, I think the reason time would have a heat increasing effect on a food would be that the seeds from the pepper have time to “soak” in the surrounding food, allowing the spiciness (capsasin) to leach out of the seed. For a dish made spicy with something like Tobasco™, I have not noticed a similar heating effect with time.

Astro points out that the microwaves act on water molecules being heated by boiling them. Steve-o notes that a day in the refrigerator spices up the concoction, too.
In both cases you’re losing water (one by boiling and one by evaporation). Julia Childs would point out that you are “reducing the stock.” What is left behind will be more concentrated.
What is left behind in these mixtures is capsasin. Remember that the “heat” of capsasin is measured by its parts per equal parts of whatever else it’s mixed up with (including water).

“Madd does a dumb thing with hot stuff”

A few years ago, I grew (for the first time) a spectacular garden of jalapenos and chili peppers.

I wanted to dry the chilies, but I did not want to wait for mother nature. Suddenly, a 1/2 watt light bulb sputtered to life above my head; why not microwave the peppers? It should dehydrate them perfectly."

Therefore, Madd goes and does this. The nuke oven hummed along nuking the peppers. After a while, I could no longer see the peppers because of the STEAM. (See where I’m going with this?)

“Better check the peppers before I burn them”, I said to myself. So, I opened the microwave door.

I immediately dropped to the floor. My eyes, mouth, throat, nose and face were on fire. I had maced myself with a pepper spray of my own creation!

It may not have doubled the ‘hot’ of the peppers, but kids, don’t try this at

I’ve wondered about this as well. I’ll eat leftovers straight out of the refrigerator, and they are definitely less spicy than when I microwave them. I’ve always assumed that it wasn’t the heating that caused spiciness, but rather the refrigeration that subdued it, by chilling your tastebuds. I’ve never gotten scientific and tested with room temperature.

Actually, when I refrigerate my salsa, I put it in Tupperware. My water loss is minimal, but it is definitely hotter the next day.