In baking, egg yolks make a significant contribution to structure, flavor, color, and moisture. Their most important contribution, however, is texture. The natural emulsifying agents contained in egg yolks help suspend ingredients evenly, resulting in a smoother mixture and finer texture.
Many years ago, I started to notice (just by looking) that egg yolks had become smaller in size. Because I weigh my ingredients, I also discovered that when my recipe called for 5 yolks, I now needed to add sometimes as many as 3 extra ones to achieve the correct weight and volume.
But it wasn’t until I taught a class at King Arthur Flour, and complained about the egg yolk situation, that I learned why egg yolks had become smaller for eggs graded the same size (that is, large). One of the students who raised hens said that when the hens are younger, the eggs they lay have a smaller proportion of yolk to white (and a chart in a 1997 research paper from the University of Iowa confirms that younger chickens lay eggs that have 10% less yolk to white). Another factor is that the total number of eggs in a crate is required to add up to 24 ounces/680 grams but each individual egg may vary in size and therefore quantity of yolk.
In recent years, when making génoise, I was disappointed that the texture had become coarser and less velvety than in years past. A génoise is made by beating whole eggs, so it took a while for it to dawn on me that a 4-egg génoise was getting the equivalent of only 3 yolks, which contributed to the textural problem. I now recommend adding an extra egg yolk to compensate for the smaller yolks without throwing off the general balance of the eggs. For a 4- or 5-egg génoise, you’ll likely need to add 1 extra yolk; for a 6- to 8-egg génoise, 2 yolks; and for a 12-egg génoise, you’ll want to add additional 4 yolks.
(The alternative would be to separate the eggs, weigh or measure the yolks and whites, and then recombine them—a process I don’t dare suggest at the risk of being considered excessively over the top!)
In any recipe calling for all yolks or a large number of yolks, my recent books give a range for the number of egg yolks in addition to the weight and volume, based on the assumption that 1 yolk equals 18.6 grams/1 tablespoon plus 1/2 teaspoon/17.2 milliliters.
The discrepancy will make the biggest difference in sponge-type cakes (most, unlike the génoise, call for separating the eggs, making it easy to weigh or measure and compensate for the smaller yolks). Because many sponge cakes depend on eggs alone for leavening (rather than more-controllable chemical leaveners), the exact amount of egg is very important. If one doesn’t weigh or at least measure and, instead, adds whole eggs willy-nilly, the cake will have a disproportionate amount of white, and the cake will balloon out of the pan. For more easy-going cakes, the exact amount of yolk and white is not as critical to the end result.
In my books, I don’t give a range if the recipe calls for only 1 or 2 yolks, but starting with 3 yolks, here is the range (the first number represents how many yolks you’d need with a standard-sized egg yolk; the second number is how many you may need to use to arrive at the correct volume and weight):
- 3 to 4 yolks
- 4 to 6 yolks
- 5 to 8 yolks
- 6 to 10 yolks
- 7 to 11 yolks
- 8 to 12 yolks
- 1 pound (454 grams) bittersweet chocolate (fine quality that you love eating, no higher than 62%)
- 1/2 pound (2 sticks, or 227 grams) unsalted butter, room temperature
- 6 large eggs (300 grams, out of the shell), room temperature if possible
- Equipment: One 8-inch spring form pan at least 2 1/2 inches high, buttered, and bottom lined with buttered parchment; outside of pan wrapped with a double layer of heavy-duty foil. One 10-inch cake pan or roasting pan to serve as a water bath
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