Be sure to look for a product that is just egg whites.
If you cannot find pasteurized egg whites, you can use regular eggs and pasteurize the egg whites: In a small saucepan stir together 2 egg whites, 2 tablespoons granulated sugar, 1 teaspoon water, and 1/8 teaspoon cream of tartar just until combined but not foamy. Heat and stir over low heat until mixture registers 160 degrees F on an instant-read thermometer. You may see a few pieces of cooked egg white in the mixture. Remove from heat and place saucepan in a large bowl half-filled with ice water. Stir for 2 minutes to cool mixture quickly. Place egg white mixture in the large mixer bowl. Continue as directed in step 4.
Cooking to the correct temperature is crucial when making most candies, ensuring toffees turn out crunchy and caramels stay chewy. Our Test Kitchen prefers a digital thermometer with a clip to attach it to the side of the pan. Before making candy, always calibrate the thermometer per manufacture's instructions.