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 of their crops over the past month or so. Cindy Chapman, who raises corn, beets and other vegetables, said she noticed that the radishes she harvested earlier in the year were especially flavorful.