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While I was reorganizing my freezer the other day so my wife could easily pull out the frozen dumplings without having to touch alligator legs, goose feet, or any number of other "experiments" going on in there at the moment, I came across a stash of rendered animal fats—beef, duck, and lamb, to be precise.

I'm the kind of cook who doesn't like throwing anything away, and sure, duck, beef, and lamb fats have their uses (think confit, burgers, or fried potatoes). But seriously—even I can't think of a way to consume a pint of each, and my freezer was getting awfully full.

Just as I was about to pack it in and tip them into the trash, I had one of those moments where jumbled images come swimming into your brain and suddenly crystallize into something so perfectly obvious that you start to say to yourself, "why didn't I think of that?" before happily realizing that you just did.

Afraid that the image might soon disappear, I grabbed a pad and paper like Ethan Hawke in Explorers and quickly sketched it out. Here's what was in my head:

I thought to myself: "If I can make mayonnaise out of egg yolks and oil, why can't I make mayonnaise out of egg yolks and rendered animal fat?"

Turns out, it's not so simple.

Mayo Basics

In its loosest definition, mayonnaise is a flavored emulsion of minute particles of fat suspended in water. The tiny globules of suspended fat have a very difficult time flowing around once they are separated by the thin film of water, which is what gives mayonnaise its viscosity. Similarly, small bits of fat will refract light to a much greater degree as it passes through, giving mayonnaise its opaque, white appearance. (Think of it like a block of glass. When it's whole, light passes through easily. But break it up into tiny bits, and it becomes opaque.)

Now normally, when you mix fat molecules with water, no matter how thoroughly you combine them, like MIT nerds visiting an all-girls college mixer, they eventually separate themselves and regroup. Because of their shape and electrical charges, fat molecules are mutually attracted to each other, while simultaneously being repelled by water.

This is where egg yolks come in. Egg yolks—which are complex fat and water emulsions in themselves—contain plenty of emulsifiers, the most important of which is lecithin, a phospholipid found in both the low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs) abundant in eggs. Emulsifiers are long molecules that have a hydrophilic (water-loving, fat-hating) head, and a hydrophobic (water-hating, fat-loving) tail.

When egg yolks, water, and oil are whisked together, the fat-loving heads of the lecithin molecules bury themselves in the minute droplets of fat, exposing only their tails. These tails repulse each other, preventing the fat droplets from coalescing, and suddenly making the water seem much more attractive to them. A bit like adding a shot of booze to that nerd fest to mix things up a little.

To make a traditional mayonnaise, egg yolks, water, salt, and a few flavorings—usually Dijon mustard and lemon juice or vinegar—are whisked together vigorously while simultaneously slowly drizzling oil into the mixture (a food processor makes this process nearly foolproof). As the oil hits the bowl, the rapid action of the whisk quickly breaks it up into tiny droplets, which are kept suspended with the help of the emulsifiers in the egg yolk.

As the sauce gets thicker and thicker, its viscosity makes it easier to break the oil into minute droplets, and as a result, oil can be added more rapidly. The final result is the rich, creamy, mild-flavored condiment we all know so well.

Fiddling with Fats

So back to the question at hand: making mayonnaise out of animal fat.

For my first attempt, I simply melted some beef fat in the microwave (because of it's high saturated fat content, beef fat is a waxy solid at room temperature), keeping the temperature as low as possible, so as not to cook the egg yolk. I made a mayonnaise exactly as I would have done with vegetable oil. Almost immediately, the mayonnaise broke (the fat and water separated), its smooth, glossy sheen transforming into the dull matte texture of shortening right before my eyes.

OK, not a big deal, I thought. Just because I haven't broken a mayonnaise in years, doesn't mean it can't happen, right? I tried again, the exact same way, and once again, my emulsion broke. I don't take failed experiments lightly, and this time I was angry enough that my wife had to ask me to stop yelling at the suet.

Still mumbling, "damn you, beef fat," under my breath, I hit the books looking for an answer as to why my emulsion wasn't holding. McGee? Nothing. Corriher? Nothing. Wolke? Nothing. Not a single mention of animal fat emulsions in any of my go-to references.

I knew that the main difference between animal fats and vegetable fats is that animal fats contain a much higher proportion of saturated fatty acids. Fatty acids are essentially a long chain of carbon molecules. In saturated fats, each of these carbon molecules has two hydrogen molecules bonded to it. These hydrogen molecules act kind of like a support system, keeping the fatty acids long and straight. On the other hand, unsaturated fats (a fatty acid that contains one or more carbon molecule missing a one of its two hydrogen partners), have a bent, kinked shape. Oddly enough, with fatty acids, threesomes are actually less kinky than pairs. The chart at the right indicates percentage of saturated fatty acids to overall fatty acids in common fats, with butter being the most highly saturated at 62%, and olive oil with a mere 13%. I knew that the main difference between animal fats and vegetable fats is that animal fats contain a much higher proportion of saturated fatty acids. Fatty acids are essentially a long chain of carbon molecules. In saturated fats, each of these carbon molecules has two hydrogen molecules bonded to it. These hydrogen molecules act kind of like a support system, keeping the fatty acids long and straight. On the other hand, unsaturated fats (a fatty acid that contains one or more carbon molecule missing a one of its two hydrogen partners), have a bent, kinked shape. Oddly enough, with fatty acids, threesomes are actually less kinky than pairs. The chart at the right indicates percentage of saturated fatty acids to overall fatty acids in common fats, with butter being the most highly saturated at 62%, and olive oil with a mere 13%.

The shape of saturated fat molecules must have something to do with my mayo's problems—after all, asides from minute amounts of flavorful molecules, saturation level is essentially the only difference between vegetable fats and animal fats—but what exactly was going on?

I emailed my friend Guy Crosby, an associate professor at Harvard and Framingham Universities and science editor at Cook's Illustrated for some answers. My hunch was right: shape is everything. Here's what he had to say.

Saturated fats (triglycerides) contain very linear fatty acids that can pack together and form crystals, sort of like a bunch of pencils in a box. Unsaturated fatty acids are bent like a V-shape, so they pack very poorly and do not tend to crystallize until much lower temperatures. The tendency of saturated fats to crystallize means they will be much less likely to form microscopic droplets that can be stabilized by emulsifiers such as lecithin in eggs. Instead there will be a greater tendency for the saturated fats to separate from the unsaturated oil and water to form more stable crystalline structures. In other words, the saturated fat molecules have a greater affinity for each other than they do for the emulsifier or the oil.

With this in mind, finding the solution was simple. All I had to do was increase the ratio of unsaturated fat to saturated fat. In a more dilute solution, the saturated fat molecules are less likely to come in contact with one another, and therefore less likely to form the crystalline structures that were interfering with my emulsion. With this in mind, finding the solution was simple. All I had to do was increase the ratio of unsaturated fat to saturated fat. In a more dilute solution, the saturated fat molecules are less likely to come in contact with one another, and therefore less likely to form the crystalline structures that were interfering with my emulsion.

The higher the level of saturated fat in a given rendered animal fat, the more I had to dilute it with vegetable oil. Serendipitously, this turned out to be a good thing for flavor —highly saturated beef is powerful enough that even when diluted five to one with vegetable oil, the spread positively screams beef. I quickly whipped out three break-free animal-fat mayos, or meatonnaise, as I'll now refer to it.

So, you may be asking, how does it all taste in the end?

Duck Fat

The duck fat meato, was fabulous. Light and creamy, with just a hint of duck flavor—not so much that it overwhelms the palate, but enough that it makes you sit up and realize: this ain't no Hellman's. Like a regular mayonnaise, the duck fat meatonnaise is great for taking on and delivering other flavors. For instance, a bit of Thai curry paste sitting in my fridge transformed it into a lickably good fragrant, spicy spread. I'd imagine some canned chipotles or Korean chile-bean paste would work equally good wonders.

Spicy Duckonnaise recipe »

Beef Fat

Beef fat meato was bordering on the obscene—lightening it up with a significant amount of water and lemon juice, and adding a bit of garlic to cut into the overwhelming beef flavor, was the key to making it palatable. This one will be reserved for special, indulgent occasions, and perhaps a bit more testing in the future—there must be some application somewhere in the realm of burger sauces.

Garlic Beefonnaise recipe »

Lamb Fat

As for the lamb, no matter how much I diluted the fat, the flavor is simply too powerful and the texture is just too heavy. If anyone wants to play with it at home and can think of a suitable application, I'd be interested to hear it. The only use I can think of is in protecting your taste buds from the ravages of the merciless peppers of Quetzalacatenango.

It was only after I'd wrapped up my testing and started writing up my results that I realized that I missed the most obviously delicious variant: Baconnaise

Bacon Fat

I truly believe that once this stuff gets out and everyone starts making it, it'll be the new "it" condiment. What could be better for dipping your fries or spreading on your burger? I've only started to skim the surface of the applications of this rich, smoky spread, but if my simple open-faced sandwich of toast, tomatoes, and bacaonnaise is any indication, I've got a long, tasty road ahead of me.

Baconnaise recipe »

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