Answers to Go with Susan Smith
Q. My grandchildren are coming to town early for Christmas. They have always loved hot chocolate. Actually, we all do. However, sometimes a "skin" forms on the milk while I am heating it. Is there some trick to preventing that?
A. I pulled “Hot Drinks: Cider, Coffee, Tea, Hot Chocolate, Spiced Punch, and Spirits” in search of this reader’s answer. Lots of recipes, but sadly no food science.
She checked out the book thinking that since they’re now adults, they might like some sophisticated variations on hot chocolate. Of course, the holidays are about tradition so there is a good chance they just want Grandma’s hot chocolate.
I did find this answer to the question at www.food.answers.com: “The skin is made up of solid proteins that combine with the milk's fat molecules, which begin to evaporate as the milk is heated. These proteins, casein and beta, clump together when the liquid reaches a temperature of around 45 to 50 degrees Celsius (or 113 to 122 Fahrenheit.)
“As heating continues, the soft protein layer begins to dry out, which is why the milk forms a skin on the liquid's surface. This layer of skin forms a hard barrier, causing steam to build up beneath it and increase the liquid's temperature. When left alone, this often causes the milk to boil over.
“Though milk forms a skin when heated in most cases, there are several ways to prevent this skin from forming.
“If you plan to heat the milk over the stove, frequent stirring will break up the protein and fat molecules, so that the membrane will not develop. If you are heating milk in a microwave, you can place a wax paper lid known as a "cartouche" on top of the container, which will slow the evaporation process and maintain the milk's liquid form.
“The milk forms a skin only on heated milk that contains fat. If you are heating skim milk, there is no danger of a skin forming on top. Because skim milk contains no fat, the protein molecules have nothing to bond with, and are unable to coagulate.”
Let’s go back to “Hot Drinks.” Here is a sample of this book’s variations on hot chocolate: Paris After Dark, Mayan Hot Chocolate with Chile and Orange, Hot Milk Chocolate and Vanilla Ice Cream Soda, St. Nicholas’ Reward, and Snowflake Vanilla White Chocolate.
