What Are Soft, Medium, and Stiff Peaks?: In baking, peaks refer to the stiffness of cream or egg whites when air has been beaten into them. As cream or egg whites are whipped, more air is incorporated, and the mixture becomes thicker. To assess the peaks, stir your mixture with your beater or whisk, then lift it out of your mixing bowl, turn it upside down, and look at the peaks of egg whites or cream coming off the mixing tool. Soft peaks barely hold their shape. Medium peaks hold shape, but the peaks curl at the tip. Stiff peaks stand straight up and do not curl over, or curl just slightly at the tip.
When Peaks Matter in Baking: When whipping egg whites or cream.
Tips for Whipping Cream and Egg Whites: Cream needs to be cold to hold a web of air and thicken, while egg whites whip up much quicker when they are at room temperature, or slightly warm, than when cold.