What is the right ratio of egg in a custard base?
What happens when you add more egg yolk?
What happens when you add more egg white?
What happens when you add more milk?
An egg, and 2/3 cup milk. After that, sweet, savory, spiced, herbed… as Lindsey Buckingham said, “you can go your own way.”
It’s that simple, and yet it’s also much more complicated than that. You could take that information as gospel, abide by it every time you make French toast, and you’d wind up with great results, every time. And though having any number of recipes committed to memory is fundamentally a practice necessary in becoming a better cook, so too is the idea that you should know why things work, so that when you’re developing a new recipe, or something seems wrong or broken, you can problem solve and fix it.
To accomplish this, we’re going to go through the two main elements of the custard base referenced above, so you can better understand the role that it plays in the cooking process.
The Egg
According to the USDA standards, a large egg weighs about 2 ounces, and specifically their guidelines require an egg to be at least 57 grams. Now, as much as you might be groaning to yourself as I say this, the next bit here will be broken down by the gram, because I think it’s easier to understand the proportions with whole numbers rather than fractions.
If a large egg weighs 57 grams:
9 percent, or just more than 5 grams, of the egg’s total eight is made up by the shell, which you’re throwing out.
Thirty percent, or just over just over 17 grams, of the egg’s total weight is made up by the yolk.
Sixty-one percent, or just about 35 grams, of the egg’s total weight is made up by the yolk.
Sciencedirect.com says that an egg yolk is comprised of 16% protein, 32% lipids, and 50% water (that last two percent? I wouldn’t worry about that little guy), so by weight, just short of 3 grams is protein, about five and a half grams is fats and emulsifiers, and about eight and a half grams is water. In contrast, an egg white contains about 90% water and 10% protein, which amounts to about 31.5 grams and 3.5 grams, respectively.
So what does that mean for your cooking, and specifically cooking French toast?
Let’s start with a separate question that’s all part of the same dialogue: why do I provide all these specifics about the makeup of an egg, but use whole eggs in every recipe?
You will, on occasion, see me produce recipes where custards don’t contain whole eggs, and to be more specific, those custards will either use egg yolks only, or have a higher ratio of yolk-to-whole-egg.
Egg yolks in a custard make it more dense and firm, and egg whites make it lighter and fluffier. These principles applied are the primary reason why, if you were making something like crème brûlée, you’d only be using egg yolks… you wouldn’t want your custard to be light and fluffy, you want it to be rich, decadent, and smooth.
As it pertains to French toast, we want both rich and fluffy, so both egg yolks and whites must be included, but is the egg’s original proportion or yolk-to-white perfect?
Based on the information above, I cracked some eggs… a dozen of them, to be exact, and I separated them into yolks and whites. I then made five batches of the base custard for French toast, one with all yolks, one with all whites, and one with whole eggs. The two remaining batches were made with an 20-80 and 40-60 ratios of yolks to whites (by weight). I dipped and cooked one slice of bread in each custard (according to the principles outlined in French toast theory), and here are the results:
<INSERT EGG TOAST PICTURE>
The all-white batch was something else… and not in a good way. As you can see, it just looks like a pile of egg whites with a weird bread island in the middle of it. Texturally, it was strangely soggy, but still cooked through. Sad.
The 20-80 yolk-to-white batch was similarly strange. I’d compare the texture to that of a damp sponge, with the additional water from a heavier dose of egg whites clearly causing issues.
The original custard is our control, so I won’t sit here and sing its praises AGAIN. It’s listed here because it maintains what is, in effect, a 30-70 yolk-to-white ratio.
The 40-60 custard was actually pretty decent. I’d argue that its differences from the whole egg base and this were nearly indecipherable. So if you can’t really tell the difference between the two, why break more eggs than you’d absolutely need?
The all-yolk batch came out almost crumbly. If you can picture the inside of an ever-so-slightly cooked hard-boiled egg, that’s a bit of the feeling you get from this. In the interest of keeping my methods constant between all of these custard bases, I resisted the urge to beat the hell out of the egg yolks to denature them, incorporate some air, which would lighten the custard a bit and make for a better texture.
The Dairy
The differing fat contents of the milk that you’re using for a custard makes for an almost imperceptible difference (unless you’re using skim milk, which is way too close to water). When mixed with eggs, whether you used 1%, 2% or whole will not matter to the final product, particularly if that custard you’re making is meant to get soaked up by a slice of bread.
What can change it, however, is using half & half, or straight up cream.
Whole milk, which to many people raised on lower fat milks can come across as undrinkably thick or creamy, tops out at about 3.5% fat. In contrast half & half (half milk, half cream) comes in north of 10% fat, while cream, depending on the type you get, ranges from 18% all the way up to close to 40% fat. But why do these percentages matter?
How rich a custard is is tied to a couple of things: how thickened it is, either by way of a gelatin or egg yolks, and how fatty it is, which affects how long each bite/spoonful stays on your palate. In the case of a custard, people often think of the richness as coming solely from egg yolks, probably because the yolk carries the fat in the whole egg, but in my opinion, the yolk is really there to provide an element to firm up the dairy. The custard’s perceived richness can be most easily changed and manipulated just by using a dairy product with a higher fat content, whether it be half & half or cream, or even a different combination of milk and cream, if you’re feeling brave.
Similar to the informal experiment above, I made three batches of a one-egg custard base, one with whole milk, one with half & half, and one with heavy whipping cream, and cooked them under the exact same conditions, and here’s a visual representation of each slice:
<INSERT DAIRY TOAST PICTURE>
The whole milk custard came out as French toast exists in your brain. The half & half version came out slightly thicker, but it stayed on the palate for much longer. The cream rendition came out like pudding.
Calling back really quickly to the mention of a custard that is thickened via gelatin, a panna cotta is a prime example of how drastically the richness of a custard can be changed, just by switching out the dairy product that makes up the base. If you made panna cotta with, say, whole milk, you’d get a completely different experience than if you made it with half and half, and again a completely different experience from heavy whipping cream.
So why are we talking about this?
Ideally, having read this, you now have some tools at your disposal. Anyone can follow a recipe, but, as I have mentioned before, not all recipes are good ones. Cooking is about balance and problem solving, and simply following a recipe without having a concept of what’s happening in it and why won’t equip you to solve problems when they arise.
If you run into an issue where your custard isn’t setting properly, remember that egg yolks are responsible for that function, so maybe your base needs more? If the custard seems too thick, remember that the dairy, and its associated fat content is responsible for that, and adjust accordingly. For French toast, specifically, something we haven’t talked about, here, is that not all breads are created equal. The type of bread, how thick it was sliced, and how dry or stale it might be will affect how much custard it can soak up, which will affect how the custard that you made reacts. If you have a two-inch thick slice of bread for French toast, you’ll need to adjust your heat down to make sure you don’t burn the outside of the toast before the inside is cooked. You’ll also need to add more egg yolk and dairy fat so that the custard is less wet, and doesn’t run out of the bread as it cooks.
Again, it’s all about finding the balance.
Also, if you find something wrong with a recipe… write down how you fixed it. This is why when you make your grandma’s recipes nothing ever turns out as good as when she made it. She left some stuff out, and you’re meant to figure out how to fill those gaps on your own. I’m not saying it was intentional, but I’m also not saying it wasn’t. I don’t know your grandma.