As I've mentioned (and demonstrated) before, I always leave New York City inspired by its bustling and ever-evolving culinary creativity. About a year ago, I went to Mario Batali's Otto Pizzeria and had one of the more revelatory ice cream flavors in my life--olive oil gelato. E recommended it, and I was admittedly skeptical, but since she's usually right about these kinds of things, I took her word for it. It was surprisingly delicious, with the subtle taste of olive oil all wrapped up in soft, sweet cream. I had it a second time from Capogiro, the famous Philly gelateria known for their unique flavors and use of local, fresh ingredients.
So I was reminded recently that this was a flavor I had yet to try my hand at, and plus I had all the ingredients at home. The recipe comes from The Babbo Cookbook, and the first thing I noticed is that the egg yolks are not cooked. As in, it does not require you to make a custard. I know, it isn't ice cream that we're making, but I didn't know that gelato sometimes contains raw egg yolks. Then again, I've never made gelato before, but I had the notion that the only difference is that gelato uses only milk whereas ice cream uses cream and milk.
Another thing I heard was that gelato contains less fat than ice cream. This apparently is true. Wikipedia states: "Gelato differs from ice cream in that it has a lower fat content, typically 3.5% for gelato versus 10-12% for ice-cream." That was another reason why the Babbo recipe baffled me, because it actually contains the same proportion of ingredients as my usual ice cream base does, and that includes cream. Weird.
The only difference then, is that for ice cream I heat the milk, whisk the hot milk into the beaten yolks, and put the whole thing back on heat to cook the eggs which thickens the mixture into a custard. For the gelato, I basically mixed all ingredients together cold, and they even say you can throw into the ice cream maker right away. This means that, because the heating process is missing, the bonds between the yolk proteins do not break (even through "ribboning", as Harold McGee describes in On Food and Cooking: The Science and Lore of the Kitchen), and the usual net-like matrix of unraveled proteins does not form as it does during cooking. Thus the gelato mix has a lower viscosity than traditional custard (which can be seen immediately upon making the mix), which affects "body and mouthfeel" of the eventual frozen product.
Qualitatively, the gelato certainly did not freeze as firmly as previous ice creams had, and had more of a "whipped" quality. But overall, it still turned out decently, but I would warn those that try to actually use a high quality olive oil. I used a mediocre olive oil because it was what I had on hand, and it gave me a bit of a strange aftertaste. Any tips on making gelato, feel free to contribute!