It's a substance so illegal that stores here in the dairy state can be fined for selling it. The great irony? That substance is butter.
To the legion of fans who have taken to social media over the last year, Kerrygold Irish butter is a gift from the dairy gods, and its disappearance from store shelves is nothing short of a travesty.
Jean Smith loves the butter so much, she has a couple-month stash squirreled away in her Waukesha fridge.
It's a stockpile of butter she regularly buys in Nebraska and drives back across state lines.
"You can do a taste test, you have to do a taste test and see I guess, but it definitely has a different richer taste than the other butter does," Smith said.
Smith is a daily drinker of so-called "bulletproof" tea. The recipe varies, but always involves blending butter into a cup of the steaming hot brew to start the day.
When Smith makes her morning tea and her husband's "bulletproof" coffee, Kerrygold is the butter of choice.
Or it was, until the self-styled "pure Irish butter" started vanishing from store shelves.
"I want to please ask whoever it is that's preventing me from getting butter in our stores here to stop it, to stop it," Smith said.
The issue here is an obscure state law from the 1970s that requires all butter sold in Wisconsin to be tested by a panel of experts and issued a letter grade for quality.
As a butter made in Ireland, Kerrygold is not graded in the U.S.
Lisa Miller is the marketing director for Ornua North America, the Irish dairy co-operative that markets Kerrygold butter in every U.S. state except Wisconsin.
She said the company had no idea selling Kerrygold in Wisconsin was illegal until the state began contacting distributors about the law.
"Our process of inspecting is a little bit different from the process here, the standards are universally very high," Miller said.
For Wisconsin, not high enough.
State statute spends pages detailing the steps needed to sell butter, and the 32 different quality points on which it needs to be judged.
Violating the butter law can result in fines upward of $1,000, or jail terms of six months.
People like Jean Smith wonder what that law is really doing -- shielding shoppers from inferior butter or fending off foreign competitors from Wisconsin's dairy industry.
"I feel suspicious. Who are you really trying to protect here? Are you protecting the consumers, are you protecting Wisconsin dairies?" Smith asked.
A spokesperson for the Dairy Business Association, an industry lobbying group, did not return our request for comment.
The state agency enforcing this law would only say what we already know.
A representative of the Department of Agriculture Trade and Consumer Protection said Kerrygold is making a conscious effort to follow the state law and adapt to Wisconsin requirements.
Lisa Miller confirmed a potential fix could be in the works.
"So we're working on some options that will meet their requirements for the way the inspection process has to work," Miller said.
Until Kerrygold and the state work that out, Jean Smith will keep doing what she's been doing - driving to Nebraska to buy her beloved Kerrygold by the carton.
"I just think it's a little goofy that this exists and I can get it in any other state that I travel in and I'm hauling Kerrygold back in my suitcase and my coolers," she said.
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