The Exact Temperatures at Which Egg Whites and Yolks Set

One of the more useful facts in practical cooking is that egg whites and egg yolks do not set at the same temperature. Whites begin to firm at approximately 62 degrees Celsius (144 degrees Fahrenheit) and are fully cooked by about 70 to 72 degrees Celsius (158 to 162 degrees Fahrenheit). Yolks begin to thicken at approximately 65 degrees Celsius (149 degrees Fahrenheit) and set fully at around 70 to 73 degrees Celsius (158 to 163 degrees Fahrenheit). The difference is only a few degrees, but it creates a narrow window where a yolk can be cooked to a custard-like gel while the surrounding white remains fully set. This window is the physical basis for sous vide eggs. ## Protein Chemistry of Coagulation The white and yolk have entirely different protein compositions, which accounts for their different setting temperatures. Egg white proteins are primarily water-soluble globular proteins (ovalbumin, ovotransferrin, lysozyme) suspended in an aqueous phase. Egg yolk proteins are primarily lipoprotein complexes (low-density lipoproteins, high-density lipoproteins, phosvitin) suspended in an emulsified fat-water system. The molecular environments are fundamentally different. In the white, denaturation of ovalbumin begins at around 62 degrees Celsius. Ovotransferrin begins to denature at an even lower temperature (around 57 to 61 degrees Celsius), contributing to early gel formation. Lysozyme is more heat-stable and denatures at higher temperatures. As these proteins unfold and cross-link, they form the protein network that gives set white its solid texture. In the yolk, the dominant coagulation comes from the denaturation and cross-linking of the lipoprotein complexes. The fat content of the yolk (about 33 percent of solids) changes the molecular environment significantly. Fats can act as plasticizers in protein networks, moderating the firmness of the final set. A set yolk is less rubbery than a set white because fat molecules interrupt the protein cross-linking, preventing the network from becoming as tight. ## The Sous Vide Window Commercial sous vide immersion circulators allow water temperature to be held within 0.1 degrees Celsius of a set point for as long as needed. This precision makes it possible to exploit the temperature difference between white and yolk setting points. A common sous vide egg preparation holds the egg at 63 to 65 degrees Celsius (145 to 149 degrees Fahrenheit) for 45 to 75 minutes. At 63 degrees, the white is just barely set, opaque but very tender, almost silky. The yolk has reached the lower boundary of its coagulation range and is thickened to a custard-like consistency but still flows slightly. At 65 degrees, the white is more firmly set and the yolk is gel-like. The same temperature windows are relevant for any precision egg cooking, including using a thermometer with conventional methods. Scrambled eggs held at 65 to 70 degrees Celsius produce a very creamy result because the proteins have barely set and retain significant moisture. Scrambled eggs cooked quickly in a hot pan reach 90 degrees or more in the curds before the pan is removed, producing a firmer, drier result. ## Implications for Food Safety Pasteurization of eggs (to eliminate Salmonella) requires reaching and holding temperatures that are within the cooking range of egg proteins. In-shell pasteurization protocols hold eggs at approximately 57 to 58 degrees Celsius for 75 minutes, killing pathogens while keeping the proteins below their coagulation temperatures so the egg appears visually raw. The white is slightly more viscous after pasteurization and whips slightly less effectively, but the egg is otherwise functionally unchanged. For everyday cooking, a thermometer removes guesswork. Egg-based sauces (custard, hollandaise, pastry cream) should reach 70 to 72 degrees Celsius (158 to 162 degrees Fahrenheit) to both set correctly and ensure food safety.