Creamy, savory cheese fondue is an ideal appetizer for a cool winter evening. Making cheese fondue is a simple process requiring only a few ingredients: garlic, white wine, shredded cheese and kirsch, which is a cherry-flavored liqueur. Combine and heat the ingredients, and if all goes well you will have a luxurious appetizer. Sometimes, the heating process does not go as planned, however, and fondue becomes lumpy. This lumpiness can result from undercooking the fondue, improperly aged cheese or overcooking. Most of these problems can be easily remedied.
Stir the cheese constantly while heating it over low heat. If you are using Swiss, Gruyere or Emmentaler cheese, the cheese may not be heated enough. These cheeses often take time to melt completely.
Add 1/4 cup more Gruyere if you are sure that you heated your fondue correctly. If the Swiss or Emmentaler cheese wasn't matured correctly, it will melt in a lumpy fashion and might not melt completely. Adding some additional Gruyere cheese may reduce the lumps by diluting the amount of improperly aged cheese because Gruyere is not likely to melt with lumps.
Add 2 tbsp. warm white wine to the fondue if the cheese is forming lumps after it initially melted. Your cheese may be lumpy because it is overcooking. The wine must be warm or it will make the cheese even lumpier. Heat the fondue on low and stir in the wine until the lumps disappear.
Add in 1/2 tsp. cornstarch and stir it in if the cheese is separating from the wine. The cornstarch is a last resort because it can change the texture of the fondue, but it will help bind the cheese and the wine together.