The food trucks lining downtown Minneapolis streets at lunchtime have mostly closed up shop now that colder weather has arrived. But city health inspectors might still be out there looking for them.

As many diners know, finding a specific food truck is a crapshoot even at the height of summer. Sometimes, inspectors have a hard time finding them, too.

As a result, about one-quarter of licensed food trucks in Minneapolis haven't been getting an annual inspection from the city's Health Department.

Of the 95 food trucks licensed to operate in Minneapolis two years ago, at least 29 percent were not inspected that year. Last year there were more trucks, and 25 percent went without inspection, according to a Star Tribune analysis of inspections data provided by the city.

Inspectors find and inspect most food trucks during peak spring and summer months by showing up at popular gatherings, festivals and farmers markets.

Near the end of August, they start looking for specific trucks they haven't yet inspected.

They might check social media or cruise the city. Eventually, they might call the food truck owner. If they can't find the truck or if the truck is done operating for the year, inspectors will mark it "not in operation."

When inspectors tried to find trucks after September, they were largely unsuccessful. Two years ago, 81 percent of these late inspection attempts failed; last year, 51 percent failed.

Almost all of the food trucks that were ultimately not inspected in 2015 and 2016 were listed as "not in operation," although a few cases involved trucks that either started late or went out of business in the middle of the season.

Aren't there regulations for this sort of thing? Here's the kicker: Minnesota health codes don't specify how often food trucks should be inspected.

"The biggest reason is the transient nature of the business," according to Steven Diaz, manager of food, pools and lodging services at the Minnesota Department of Health. He said food trucks have been exempt from annual inspection requirements for several decades.

Diaz emphasized that food trucks should still be inspected; the state just doesn't say how often. "It's more of a judgment call on our part," said Dan Huff, director of the city's Environmental Health division.

The city has 19 staffers who inspect more than 5,000 facilities, Huff said. That includes restaurants, hotels and pools. Some facilities have multiple licenses to inspect, like U.S. Bank Stadium, which has about 150 licensed operations.

When the city began regulating food trucks in 2010, it issued 10 licenses. This year there were 143. The jump from 2016 to 2017 was the largest annual net increase in the eight years of the program.

"Some years are stagnant, and some years we have a boom," said Amy Lingo, district supervisor of business licensing for Minneapolis. "This year was a big one."