And the mystery ingredient is… flax seed.

The stem of the flax plant, as you well know, is the source of linen fibers, and the seeds are used to make linseed oil, which is used to produce oil paint, printer’s ink, and linoleum, among other non-food items. But the seed has also been embraced by nutritionists and vegetarians as an excellent source of calcium, iron, niacin, and vitamin E. It is also heralded as a rich source of the much-sought-after Omega-3 fatty acids, for which you would otherwise have to consume fish. And the very idea of that is offputting to a large percentage of vegans.

So what does this have to do with egg whites? Flax seed also has the wonderful quality of being naturally mucilaginous. Ground to a fine powder and mixed with water, flax seed turns into something that looks very much like egg whites and acts something like them. Vegetarians substitute this mixture for egg whites in a number of recipes, such as pancakes, muffins, and cookies.

Flax-seed-egg-white substitute does not have the ability to make and hold bubbles the way egg whites do, so you cannot whip them into a foam, nor will they produce a leavening effect in baking. And not only is the volume of what you’re baking going to be less, it is likely to be somewhat gummier and chewier than you’d expect with egg whites.

To make flax-seed substitute, combine 1 tablespoon of milled flax seed with 3 tablespoons of water for each egg white you need. Mix it well and let the mixture sit for 1 to 2 minutes. Add to the recipe as you would an egg. You might want to test your recipe first before preparing it for guests to see if it meets your expectations.

One final possible drawback, to use the gracious words of Sharon Tyler Herbst, author of The New Food Lover’s Companion, is that, “though it is considered a digestive aid, it should be noted that, for some people, flax seed also has a laxative effect.”