This recipe comes from renown food-safety expert O. Peter Snyder who, in turn, gives credit to Bocuse and Metz.
Eggs carry a low-but-not-zero risk of foodborne illness. Egg sauces (e.g. mayonnaise, Hollandaise, Caesar dressing), being high-moisture and low-acid, increase the risk substantially. Most cooks know when eggs are heated to 150F their proteins coagulate and that emulsified sauces will break when heated. Based on this knowledge, they believe pasteurization and thus safety is not possible. Chefs often exacerbate the situation by holding sauces intended to be served warm smack in the middle of "The Danger Zone". Dangerous! And completely unnecessary.
By diluting the eggs with water and adding a controlled amount of acid, the temperature at which their proteins would coagulate is significantly raised. Further, the acid content acts to prevent subsequent microbial growth. Caution: Safety depends upon an accurate acid balance and accurate temperature measurement. You may adjust the flavoring components (sugar, mustard, etc.) but the egg-acid mixture is critical.
Combine yolks, vinegar, lemon juice, and water in the bowl of a double-boiler setup.
Place over simmering water at a temperature between 180 and 190F. Heat the mixture to 150F (about 1 min.) The mixture must be stirred or whisked constantly and the temperature measured frequently by using a tip-sensitive thermocouple thermometer (such as a Thermapen). When the specified temperature is reached, immediately remove the pan and allow to cool to room temperature (<80F).
Note: The pasteurized egg yolks are very stable at this point and can be stored for 7 days at 41F. The pH of this mixture is 3.5
Place the pasteurized, acidified yolk mixture in a stainless steel mixer bowl. Add dry mustard, salt, and cayenne pepper.
Whisk mixture (or if a mixer is used, turn it to high speed) and *very* slowly, teaspoon by teaspoon, begin adding oil. When an emulsions forms, oil can be added more rapidly. Continue beating until all the oil has been added.
Check and adjust seasoning. If necessary, viscosity may be adjusted with a small amount of vinegar or lemon juice.
Place mayonnaise in clean, sanitized storage container. Label and date product. By government standard, this product does not require refrigeration for safety. For quality, refrigerate at 41F or less. The shelf life will depend on mold contamination during mixing, but should be at least 4 weeks.
Note: If olive oil is used, the mayonnaise should be used at once. Olive oil will crystallize or solidify under refrigeration and the mayonnaise emulsion will break.
Ingredients that could produce reactions in sensitive individuals: Egg yolks, sulfites (bottled lemon juice, wine vinegar), mustard