ST. PAUL, Minn.—Heavy is the head that wears the crown at the Minnesota State Fair.

Rachel Rynda became the 69th Princess Kay of the Milky Way at this year’s fair, a peerage with duties that include whipping up support for the state’s 2,100 dairy farmers for a year.

Ms. Rynda also faces a royal dilemma: what to do with a larger-than-lifesize sculpture of her royal visage carved in butter—and buckets of shavings from the massive original block.

“I don’t know if you can picture 90 pounds of butter, but it’s a lot,” said Tina Hoff, a 2004 winner, who let everyone in her town roll ears of sweet corn over her butter bust to say thank you for their support. She said the rest kept her grandmother’s baked goods buttered for more than a decade.

Ms. Rynda, a 19-year-old college student who grew up on a dairy farm near the town of Montgomery, intends to make Christmas cookies with the scraps she received. She plans to share her butter head, too: She wants to melt it down and throw a special event for all her supporters.

Rachel Rynda is crowned the 69th Princess Kay of the Milky Way.

Photo: Joe Barrett/The Wall Street Journal

“I want to have a big movie night with popcorn and have butter with my popcorn,” she said, posing in a snowmobile suit inside a rotating refrigerated case, so fairgoers could watch sculptor Gerry Kulzer carve her creamy yellow likeness from a two-cubic-foot block of grade A butter.

Past winners have had their butter heads displayed in a museum, hauled out at their weddings or donated to school cafeterias. The nine runners-up get to take home a bust, too. Untold numbers lurk in farm freezers across the state.

“It looks pretty darn good, doesn’t it? No freezer burn or anything,” said Julie Antonutti, the 1994 winner, as she admired a butter image of herself 28 years younger, believed to be the oldest full bust still around. Her mother keeps it on the family farm south of Minneapolis in a freezer, alongside chopped rhubarb, sweet corn and hamburger.

“If you knew my mom, you’d know that she holds on to all things special to her,” said Ms. Antonutti, 49. “She’s kind of a pack rat.”

Julie Antonutti checks the 28-year-old butter head stowed in her mother’s freezer.

Photo: Joe Barrett/The Wall Street Journal

Other state fairs may have bigger butter sculptures depicting full-size cows, scenes of rural life and various other themes. None send their royalty home with such a huge edible prize.

In Illinois, Iowa, Missouri and Texas, the butter used in sprawling sculptures is scraped off the frames and put in cold storage at the end of the fair. Some sculptors reuse it for years. In Ohio, a recycler turns the butter into products such as soap, grease for metal forging, cosmetics, tires and biodiesel.

New York’s 800-pound butter sculpture, which this year depicts female athletes and a big container of chocolate milk, is processed into electricity, providing enough juice to power a home for three days. New York State Fair officials are encouraging fairgoers to use an app called the Butterizer that lets them see what they would look like as a butter sculpture.

Tae Nordby, who was crowned the 50th Princess Kay in 2003, recalls being fascinated as a little girl when her older sister, a finalist, had her head carved. “I was determined that someday I was going to be in that butter booth,” said Ms. Nordby, 37, a stay-at-home mom who works part of the year on a family apple orchard.

She remembers the nerve-racking, three-hour trip home from the fair on a 95-degree day with the sculpture she won in a box on the back seat of her Mustang. “We had the air on high and tried to keep it cold,” she said.

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Her butter head, with a gold crown instead of silver because of the 50th anniversary of the contest, was displayed at the Minnesota History Center for several years. It’s still in her parents’ freezer, along with those of her older sister and a younger one, who was also a finalist.

Ms. Antonutti, whose mother is the keeper of the oldest intact bust, said she had planned to sacrifice her butter head to a big party called a corn feed.

“As our luck would have it, my dad’s sweet corn plot got ravagely attacked that year by some raccoons,” she said. “And then life just happened, and my mom has kept it in the freezer ever since.”

Jean Kessler, Princess Kay of the Milky Way in 1980, with the face of her 42-year-old butter sculpture.

Photo: Joe Barrett/The Wall Street Journal

Jean Kessler, a 60-year-old retired dental hygienist who was crowned Princess Kay in 1980, still has the 42-year-old face from her sculpture in a freezer in her house near Pine City. Her mom, concerned about freezer space, made her trim the sculpture after the first year and eventually had her take the face with her as Ms. Kessler moved to Iowa and other states.

“We ate most of it in Christmas cookies, but I couldn’t eat the face,” she said.

She pulled it out of her freezer on a recent day. “There’s a little frost on it,” she said. “Oh, my nose is cracking a little,” in addition to being pushed in from being reboxed after her homecoming party.

Ms. Hoff, a 38-year-old stay-at-home mom whose husband is stationed at Fort Hood, Texas, was chosen Princess Kay a year after her family sold their cows when a tornado damaged their farm. The community provided so much support that at the end of her reign, she and her family threw a thank-you golf tournament and let everyone use her softening head to butter their corn afterward.

Tina Hoff looks at her butter likeness made after she won the Princess Kay title in 2004, when she was known as Tina Rettmann.

Photo: Rettmann family

“My brother and sister were all about making a mohawk out of my hair and cutting off my nose,” she said.

Abbie Warmka, a 35-year-old large-animal veterinarian in Waupun, Wis., and Princess Kay finalist in 2005, met her dairy farmer husband one day when she was examining his cows. “We hit it off,” she said.

When she suggested they get a butter sculpture of him and display both at their 2018 wedding, he was intrigued. The wedding, with a hashtag of #buttertogether, featured an area for guests to take their photos with the sculptures. “It was way over the top,” she said. “But people had a lot of fun.”

Her 13-year-old butter head was getting a little moldy, she said, so it went in the trash that night.

“But we cut up my husband’s head and ate it in cookies and on toast,” she said.

Abbie Warmka's Princess Kay sculpture next to one she had made for her husband, Erik Warmka, on display at their wedding.

Photo: Moments to Memories Photography

Write to Joe Barrett at joseph.barrett@wsj.com