The business section of Time magazine recently reported that in 2016 a journalist snapped a picture of the list of 11 herbs and spices found in the Kentucky Fried Chicken Recipe, reportedly from a family scrapbook.

Secret ingredients have been the mainstay of advertisers over the years in products as diverse as baked beans to engine oil additives. My dad was a promoter of Marvel Mystery Oil. Did it meet the claims of longer engine life and better fuel economy? Questionable, but using it made him feel better.

Mystery ingredients have long held the honor of having a placebo effect. If one of the...