By safe, we assume you mean egg whites that will not deflate just before you bring your famous showpiece dessert to the table. Actually, we know you are referring to the concern people have about eating uncooked egg.
Alice Medrich, author of Chocolat: Extraordinary Chocolate Desserts , has devised a method that takes egg whites up to the safe temperature of 160°F (70°C), and that still allows them to be beaten and then folded into a mousse or other dessert. Because of the added sugar, this is not the same thing as simply beaten egg whites, it is essentially a meringue or a variation on an Italian meringue. But, according to Medrich, you cannot raise the temperature of the egg whites high enough without adding the sugar to avoid scrambling them.
If you're making a mousse or other recipe that calls for beaten egg white, see if you can reduce the amount of sugar in the other portion of the recipe by the amount added to the egg whites, so your final result is not overly sweet.
The New Safe Meringue From Chocolate and the Art of Low-Fat Desserts, by Alice Medrich.
Safe Meringue can be used place of ordinary meringue in old recipes. These include uncooked desserts such as mousse, Bavarian cream, and ice cream, as well as soft meringues for pie topping and Baked Alaska where a short baking or browning period may not be enough to heat the meringue thoroughly.
2 Tbsp water 1/8 tsp cream of tartar 2 egg whites 4 Tbsp sugar
Bring 1 inch of water to a gentle simmer in a large skillet. Combine the 2 tsp water with the cream of tartar in a 4- to 6-cup stainless steel bowl. Add the egg whites and sugar and whisk together briskly to combine ingredients thoroughly and break up the egg white clots (which have a tendency to scramble first.) Place an instant-read thermometer near the stove in a mug of very hot tap water.
Set bowl of egg whites in skillet. Stir mixture briskly and constantly with a rubber spatula, scraping the sides and bottom often to avoid scrambling the whites. After 1 minute, remove bowl from skillet. Quickly insert thermometer, tilting bowl to cover stem by at least 2 inches. If less than 160°F (70°C), rinse thermometer in skillet water and return it to mug. Replace bowl in skillet. Stir as before until temperature reaches 160°F when bowl is removed. Beat on high speed until cool and stiff.