I tried to cook spaghetti alla carbonara and searching out I found out that some recipes use whole eggs and some only the egg yolks. Which way gives the better result?
I've asked this question to many friends of mine from Rome, and they all agree that only yolks should be used. Then I managed to find out the scientific reason behind this.
The real challenge with this recipe, which makes the difference between a perfectly made creamy carbonara and just pasta with omelette, lies in temperature control.
As a matter of fact, the problem of keeping the sauce from getting curdled arises when you mix pasta just taken out from water boiling at 100 °C with egg components that coagulate at a much lower temperature. In particular, as anyone having fried an egg knows, egg white coagulates earlier than yolk (protein coagulation temperatures are approx. 60-62 °C for the former, 68-70 °C for the latter).
This means that egg whites are more susceptible to ruin your carbonara, if you can't manage to rapidly decrease the overall temperature below 60 °C. Since egg whites function is just to provide a more fluid substratum (creaminess and flavour come mostly from yolks), they are usually left out and replaced with starchy pasta water.
So, put yolks only (one per person) in a large bowl and whip them, add pasta al dente without straining it first, using a large fork or kitchen pliers to take it straight from the pot, and then quickly mix them together while adding the remaining ingredients.
In this way, cooking water adhering on pasta surface will provide both the liquid base for the sauce and enough heat to thicken it, while the mixing will disperse the heat in excess.
The more stable sauces I've seen use the 3 whole eggs to 1 yolk ratio.
However, the reason the recipes disagree might have to do with the following:
Published March 1, 2013. Cook's Illustrated:
They suggest using half has usual water to cook the pasta and using 1 cup of the starchy pasta water to stabilize the sauce. The starch interacts with the protein in egg whites to prevent tightening.
Note: if you are using half as much water, then make sure you stir the pasta gently for the first minute of cooking the pasta and do not put a lid on the pot. Hang around the pot and make sure the starch/foam doesn't crawl out of the pot and start dancing around your kitchen.
The egg yolk only version might lead to a less creamy sauce but as suggested, it may be less susceptible to the tightening problem.
For me only ever the yolks. I don't add them to the sauce while I'm cooking. I just sit two egg yolks on top of everyone's portion covered with chopped dill and black pepper so it looks all cheffy.
This is because I want to get as far away as possible from the gooey white muck you get in a jar. The egg whites act as an emulsifier for the sauce, so the more you use the closer you get to a mayonnaise.
I like to think of a carbonara as a way of showing off a really good pancetta and a really good quality pasta. So I like to try and go for something very light and summery with few ingredients. So I don't use the egg whites because they make it too stodgy.
If your idea of a Carbonara is a thicker creamier dish then you should add egg whites. Although you can achieve the same effect by using more cheese. Add the pasta to the pan on a high heat, keep adding finely grated cheese and ladle in the water you cooked the pasta in. Too loose more cheese, too dry more water. Be careful though. I've never found a limit to the amount of cheese you can add this way, but if you add too much you might need to go and lie down for a bit after you've eaten it.
As several people have pointed out they coagulate at lower temperatures than the yolk, which can lead to a takeaway pizza, so turn the heat down when you add them. Beating them lightly with a bit of water and\or sugar helps too.
Felicity Cloake has done the hard work of comparing carbonara recipes, and her conclusion is: