What Is the Best Way To Skim the Fat From Soup and Stock?

Recipes tell you to “skim the fat” from soups and stews as if it were as easy as peeling a banana. Supposedly, you just grab a spoon and scoop off the layer of fat without removing any of the underlying solids or liquids.

But the word skim is a scam.

For one thing, it’s hard to know how deeply to scoop without removing a lot of the underlying liquid. If the pot or pan is wide, the fat may be spread out into such a thin layer that you can’t remove it with a spoon. Moreover, there are probably lumps of meat and vegetables sticking up through the surface that impede your scavenging. And finally, there can still be a lot of fat hiding down among the solids.

If there’s not too much liquid in the pot, you can pour it all into a gravy separator, one of those glass or plastic cups that look like miniature watering cans and dispense their contents from the bottom, like a crooked card dealer. The watery liquid flows out, leaving the top layer of fat behind.

Or, you can strain the liquids into a tall, narrow, heatproof glass container, so that the fat layer becomes deeper and can be sucked off the top with a rubber-bulb turkey baster.

The most tempting method is to put the whole pot in the refrigerator, so that the fat layer will solidify and you can then lift it off in pieces like ice from a frozen pond. But that’s dangerous, because the pot can heat the contents of your fridge to a bacteria-friendly temperature. Cool hot foods in several small containers before refrigerating them.

A wonderfully quick and easy method involves a midget-size mop, yes, a mop, that literally mops up the fat. You swish it across the surface of your stock (or soup or stew) and it selectively soaks up the oil without absorbing the watery liquid. It goes by various unappetizing brand names, including Oil Mop, Fat Mop, and Grease Mop, and is available at kitchenware stores.

How, you may ask, can a mop distinguish between oily and watery liquids?

An ordinary mop absorbs water because the water wets, that is, sticks to, the fibers of the mop. There is an attraction between the water’s molecules and the molecules of the cotton, or whatever the mop fibers are made of. Moreover, water will even climb up between the fibers by capillary attraction. Thus, when you dip an ordinary mop into water and withdraw it, a lot of water comes along with it.

But water doesn’t wet all substances, by a long shot; its molecules just have too little attraction to certain other molecules.

Dip a candle into water, for instance, and it will come out dry. Water won’t stick to wax or to many plastics, but, and here’s the thing, oils will. The Grease Mop is made of a plastic that is wetted by oil but not by water. It therefore sucks out only the oil.

Now that your mop is loaded with oil, and it can hold only so much per swish, how do you dispose of that oil before the next swish?

You can hold the mop under hot water and let the oil go down the drain, but it may eventually find a cool spot and solidify, clogging the pipes beyond the reach of any plumber, short of tearing the house down.

Alternatively, you can step out the back door and flick the mop smartly. A little shower of oil won’t hurt the grass, and it’s biodegradable. The ants will even thank you for it.

Then, back to the kitchen to swish and flick again, until all the fat is gone from your pot.