How much butterfat is in your homemade ice cream? It’s a difficult question to answer. Recently I sat down with a pencil, a stack of paper, and a big eraser, with a mission to make an online butterfat calculator . I decided to start with a Sweet Cream Base recipe  of cream, milk, eggs, and sugar. Should be simple enough.
The first problem was figuring out how much butterfat is in each ingredient. Even if you look at the labels on the milk and cream cartons, you’ll find inconsistent numbers like “5 grams of fat per 15 ml,” or “3 grams of fat per 30 ml” or “8 grams of fat per 240 ml.” These have to be converted to a percentage by volume, and then converted again to a percentage by weight.
There was no nutrition label on my carton of eggs, but it turns out that one egg is 9.94% fat by weight. Roughly. I know this because the nice folks at the United States Department of Agriculture’s “Agricultural Research Service” have a whole web site called the National Nutrient Database for Standard Reference . Or if you prefer a shorter name, the USDA AGS NNDSR. ;-) This site is filled with useful info about the nutritional content of eggs, and just about any other food you can think of. And not just plain ol’ chicken eggs… there’s info about duck eggs, goose eggs, egg substitute, hard-boiled eggs, eggnog, and dried stabilized glucose reduced eggs, too.
After scrounging the fat percentages for all the stuff in a basic ice cream recipe, I was able to calculate that Ben & Jerry’s Sweet Cream Base #1  is 19.1% total butterfat by weight. Roughly. That sounds about right, because homemade ice cream tends to be much higher in butterfat than commercial ice cream. Super-premiums like Ben & Jerry’s and Häagen-Dazs top out around 16% , but they sometimes use things like stabilizers  and NFMS (more on that below) to compensate. So our homemade versions need more butterfat to keep them smooth and creamy.
OK, great! Except that I have no way to know if my figures are correct, because Ben & Jerry’s didn’t tell us the butterfat content of that recipe. And it turns out that hardly anyone else on the internet tells the butterfat percentages for their recipes either. But fortunately Ben & Jerry’s did tell us the magic number for their Sweet Cream Base #2 , and it’s 25%. Roughly. And when I calculate it? I get 24.8%. Excellent!
After I turned my pencil scratchings into a working calculator, where you could enter all the ingredients and get the butterfat percentages back, I realized that there are two numbers for fat content. There’s the percentage butterfat, which is the fat from just the milk and cream, and there’s the percentage of normal “lipid” fat, which includes the butterfat and the fat from things like eggs and chocolate as well.
And then there’s sugar, which doesn’t have any fat at all, but does have weight. And since we’re calculating the butterfat percentage by weight, not volume (because we don’t care about the amount of air added to the ice cream), any weight we add for things like sugar will affect the overall weight, and therefore it’ll affect the overall butterfat percentage by weight as well.
And if that wasn’t enough, I decided to also throw in the percentage of “Nonfat Milk Solids,” or NFMS as they refer to it in the commercial ice cream biz. NFMS is basically the “solid” part of skim milk. So if you took a cup of raw milk, skimmed off the cream to get “skim milk,” and evaporated the skim milk down to a powder, that powder would be the Nonfat Milk Solid part of milk. Which, in case you’re dying to know, is 8.7% of milk by weight. Roughly. NFMS doesn’t play a big part in making homemade ice cream, but it does in making commercial ice cream, where they add some amount of dry milk powder depending on the amount of butterfat in the recipe. The less butterfat you use, the more NFMS you use to make up for it. But that’s another post, and an opportunity for more experiments.
I think my butterfat calculator is correct, but with a validation suite of exactly one test case, who really knows. If you have any other recipes to test it with, leave a comment below!