MILWAUKEE – Chef Dan Jacobs expected his recent batch of jalapeño poppers to be tame because peppers grown at this time of the year are generally mild. But he quickly discovered that his spicy appetizer carried an unexpected fire.

“Wow, those things are no joke. They are hot,” said Jacobs, the top chef at Roots Restaurant and Cellar in Milwaukee. “At this time of year, they shouldn’t be this hot. But the warm weather, the no rain, that’s going to cause that.”

Temperatures above 100 degrees and droughtlike conditions have baked parts of the upper Midwest for weeks, taking a severe toll on corn and soybeans.

But the heat brought an expected benefit for peppers and other crops: Their flavors became unusually concentrated, producing some of the most potent-tasting produce in years.

In peppers, that means the difference between a lightly tingling tongue and heavily watery eyes. The effect comes from alkaloids, the substance that binds to heat receptors on the tongue.

“Peppers really like hot weather,” said Irwin Goldman, a horticulture professor at the University of Wisconsin-Madison. “When it’s dry and hot outside, you’ll get a higher concentration of alkaloids.”

The same phenomenon also happens in onions, garlic and certain fruits, he said.

Scientists say a pepper’s hotness is generally determined by genetics, although environment can play a role. Long hot days cause peppers to produce more capsaicin, the specific alkaloid that delivers the spicy kick.

The absence of water also has an effect. The higher a vegetable’s water content, the larger and juicier it is, but the more diluted the flavor.

Farmers say they’ve noticed a taste difference in several crops over the past month or so. Cindy Chapman, who raises corn, beets and other vegetables, said the radishes she harvested earlier in the year were especially flavorful.

“They were much hotter, really sharp,” said Chapman, a farmer in East Troy. “Some people won’t eat them when they’re that sharp, and then there are other people who love the stronger flavor.”

This kind of weather can also cause melons to be especially sweet, said Jim Nienhuis, who also teaches horticulture at UW-Madison. Cantaloupes originated in the Middle East, and watermelons came from the deserts of Africa, so they’ve been thriving.

“Hot, dry conditions result in higher rates of photosynthesis, leading to higher concentrations of fruit sugars,” he said in an email.

Bruce Sherman, executive chef at the North Pond Restaurant in Chicago, has noticed. His restaurant gets its fruits and vegetables from farms in Illinois, Indiana, Michigan and Wisconsin, and his recent batches of cantaloupes and cucumbers have been exceptionally sweet.

Sherman said he might use cantaloupe in a melon gazpacho or a cucumber-melon-corn salad.

“We might not dress it as heavily if the integral flavor is better by itself,” he said.

Sherman said he hadn’t gotten any unusually spicy peppers yet, although one supplier told him that her jalapeños and serrano peppers were twice as hot as usual.

While fruits and vegetables with lower water concentrations can have a sharpened taste, they’ll also generally be less juicy. David Witte, a West Bend farmer, said that could be good or bad.

“One person might like that there’s more flavor but less juice, and the person next to him might like a tomato that you cut into and see the juice come out,” he said.

The current phenomenon will only last as long as weather in the Midwest remains hot and dry. The heat wave has already moderated in some places, and rain could serve to reduce the flavor concentrations.

Some cooks might take advantage of that brief window to hoard hot peppers for five-alarm chili or extra-spicy salsa. But Jacobs said he didn’t plan to offer any special dishes with his fiery jalapeños, grown in Grafton.

If anything, the extra potency means he has to go out of his way to make sure his dishes stay consistent.

“I think we’d just be more careful how we use them in salsa or sauce. We might use one instead of three,” he said. “The ones that are super-spicy are no joke. They will rip you apart.”