The Function of Fat

Reader Eva writes:

You reminded me of a question I’ve been meaning to ask. When a recipe calls for heavy cream or a specific type of milk like whole, what are the pitfalls of substituting a lower fat product (say half-n-half for the cream and nonfat for the whole)?

Hey Eva! There are consequences, but seldom catastrophic ones. Dairy fat is a moistener and flavor booster, so cutting back to skim milk from heavy cream will probably be noticeable. However if you’re just scaling things back a notch or so as you describe, you won’t detect much difference.

There are some things to watch out for when you cut fat out of a cake recipe. One is your leavening. All cake-like preparations are wars on a micro scale between the forces of “up” and the forces of “down.” Pushing up we have leavening of course, but also flour and egg whites. These are the things that create the structure…the support that holds the cake up. Pulling down we have sugar, fat, inclusions like chips or fruits, non-wheat grain flours like corn meal, even wheat bran. Most recipes you come across will have achieved a balance between these forces. Take too much of one away and the result can be a radical sinking or a radical rise…which ends in a radical sinking because the hyper-extended structure can’t support its own weight. I saw hints of over-rising when I made my lighter layers yesterday. That’s why I’m going to add a little extra flour to the formula…just for insurance.

Another thing to remember is that fatty liquids (cream) have a higher viscosity than lean ones (milk). Which is to say, they’re thicker. That can effect the way a batter or dough flows. Thus when I took the cream out of the recipe I also needed to take out the water and cut down the volume of milk a bit.

Lastly, remember that fat is a curdle inhibitor. The molecules get between the proteins in custards, providing some extra insurance in the event they’re overheated. Thus a custard made with milk will break a lot easier than one made with cream or half-n’-half. Also, as mentioned earlier in the week, milk added to caramel will curdle instantly, for the same reasons. Hope this helps!