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Day, Mildred

Published onJul 30, 2021
Day, Mildred

(September 24, 1903 – June 9, 1996) 

Quick Facts

Day was a 1928 Iowa State Graduate and inventor of the popular confection Rice Krispie Treat®. Since the snack's inception, it has remained largely popular even today.


The youngest of five children, Harriet Mildred Ghrist was born in Durham, Tennessee. Disliking the aunt for whom she was named, from a young age insisted she be refereed to as Mildred, or the colloquial Millie. Parents Charles and Mina relocated the Ghrist family to a farm in Quebec early in Mildred's life. While there Mildred attended a small one-room Quebec school and by most accounts excelled, winning spelling bees and speech/debate competitions.

Once again in Mildred's teen years the Ghrist family moved, this time to Ames, Iowa where father Charles took up custodial work at Iowa State College (now Iowa State University). Having developed exceptional writing skills in her youth she was offered a position as social editor for a local newspaper. In 1924 Mildred enrolled in Iowa State College as a Home Economics major excelling just as she did in primary and secondary school. To earn money while in college Mildred worked as a research assistant for a genetics professor at Iowa State. Being very active while in college Mildred wrote for a campus publication, the Green Gander, and belonged to a home economics organization. While attending the Drake Relays (a track and field event) in Des Moines, Mildred met James Meredith Day of Vermont and not long after entered into a relationship with him.

Prior to Mildred's graduation from Iowa State, she had lined up a job at the Kellogg's cereal company in Battle Creek, Michigan – a thriving town filled with various major cereal manufacturers including both Kellogg and Post. Charles Day asked for Mildred's hand in marriage, and with her father Charles' permission they wed in Burlington, Vermont and settled in Battle Creek.

The newlywed Days rarely ate out, Mildred being an excellent chef able to provide food as high a quality as that found anywhere else in Battle Creek. Her cooking ability was utilized by the Kellogg's company as she tested new recipes in the company kitchens. Ultimately she was sent via train cross-country to provide cooking workshops for Kellogg's customers.


Kellogg, looking for a way to further move their product Rice Krispies created in 1928, tasked Mildred and co-worker Malitta Jense with developing new recipes. After two solid weeks of trial and error the duo created Rice Krispies Treats® in 1939, a recipe that still remains largely unchanged. The two were inspired by popcorn balls, a local county fair food, but replaced the corn with puffed rice and the corn syrup with marshmallow. Six month later a Campfire Girls organization in the Kansas City area pleaded the company for fundraising assistance – Kellogg's decided to put Mildred's "marshmallow squares" to the test. Mildred was very active with the Campfire Girls as a troop leader. Day took a train to Kansas City where she set up a temporary kitchen. For two weeks, working daily from 6:30 AM to 10:00 PM, she made batch after batch of the treats while the troop mothers of the Campfire Girls wrapped the bars and the girls sold them door to door.  The treats were a huge success and in 1941 Kellogg's put the recipe on cereal boxes. The recipe spread nationally appearing in McCall's, Ladies Home Journal, Good Housekeeping, and even The Locomotive Engineers Journal.

According to Mildred's daughter, Rippie, Mildred may have also been the first to serve an airline meal. During a flight, Day prepared meals for a small group of magazine food editors invited to Battle Creek on a short excursion flight aboard a Ford Tri-Star airplane. Millie was on board to keep the prepared meals warm.

In the coming years the Days moved to Minneapolis, Minnesota where husband James put a stake in various entrepreneurial ventures and Mildred began work for the Pillsbury Company. During her tenure at Pillsbury, Day helped developed cookbooks that use more modern and precise language that focuses on more on measurements. Finally Mildred withdrew from her career and assisted her husband in operating his numerous businesses which included three Buster Brown shoe stores, a water-softener business, and a pool construction company. Through this period, Mildred still used her culinary skills as she did freelance cooking work for Meredith Publishing Company’s many magazines.

Every year Mildred would return to Ames around Easter to visit relatives, a trip she would often make with her daughter, Sandra Rippen. Her husband passed away in 1975, Mildred herself passed away in Bloomington, Minnesota on June 9, 1996 at the age of 92.

Selected Sources

History of food in 100 recipes, William Sitwell

The Star Tribune "Mildred Day Obituary", June 12, 1996, Minneapolis Minnesota.

The Breakfast Cereal Gourmet, David Hoffman

Sarasota Herald-Tribune, June 14, 1996 "Mildred Day Recipe Developer"

Milwaukee Journal Sentinel, June 13 1996 "Mildred Day Developed Rice Krispies Treats"

"I" Is for Iowa Inventors, 1998, Millie K. Frese

Blog by Mindy Moeller, Iowa State University Library Preservation Department, “Rice Krispie Treat”.

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