Most cultured milk products are especially susceptible to curdling when made into sauces or added to other hot foods. Fresh milk and cream are relatively stable, but the extended heat treatment and high acidity characteristic of cultured products have already caused some protein coagulation. Anything the cook does to push this coagulation further will cause the protein network to shrink and squeeze out some of the whey and produce distinct white particles—protein curds—floating in the thinned liquid. Heat, salt, additional acid, and vigorous stirring can all cause curdling. The key to maintaining a smooth texture is gentleness. Heat gradually and moderately, and stir slowly.