The Food Lab: A Mind-Blowing Technique for Cleaning Deep-Fry Oil Using Gelatin
I get emails from readers packed with fun stories, family recipes, and interesting tips, techniques, and questions all the time, but it's rare that I get one with a technique that completely blows my mind. This is one of those occasions.
Here's the short of it: You can use gelatin to filter cruddy used deep-frying oil until it is crystal clear, and the technique is easier than any other method I know, requiring no wire strainers or coffee filters or extensive clean-up. If you are impatient, you can jump straight down to the directions and get to clarifying, but read on for more details on the testing.
How Gelatin Clarification Works
The email I got suggested, in a nutshell, dissolving some powdered gelatin in boiling water, then stirring that hot water into used deep-frying oil before letting it rest overnight. As the gelatin settles and sets, it should end up trapping impurities in it, leaving clean oil behind.
Wait, what? This sounded way too good to be true.
The idea of using gelatin to clarify stock is relatively new. It first came to my attention around 2009 (I probably first read about it on Dave Arnold's Cooking Issues blog). Gelatin is a protein that forms an interconnected, weblike matrix when dissolved in water. Not only does the gelatin give the water structure (think: Jell-O), it can also suspend other dissolved and undissolved solids in its matrix.
To gelatin-clarify, you first freeze a gelatin-rich stock, then slowly let it defrost in a strainer or wrapped in cheesecloth. As it defrosts, the network of interconnected gelatin proteins traps impurities, letting a crystal-clear consommé drip out of the bottom, with no need to skim, strain, or simmer.
But using gelatin to clarify oil? Now that was something really new, and frankly, if it worked, far more useful for the average home cook, who probably has no need to make consommé but often ends up wondering, "Can I use this oil again?"
I was skeptical. Stock clarification works because gelatin dissolves readily in hot water. Would mixing gelatin-rich water with oil really filter out impurities, when the gelatin is not even technically dissolving in that oil? Only one way to find out.
The Testing: Fat Clarification Using Gelatin
I happened to have a small pot of particularly well-used oil on hand (previously used to fry a few batches of vegetable tempura, as well as some chicken-fried shrimp). I dissolved a teaspoon of gelatin in a half cup of boiling water, then dutifully stirred it vigorously into the dirty oil before transferring it all to an airtight container and setting it in the fridge to encourage the gelatin to solidify.
The next morning, I pulled out the container, poured the oil out into a small pot, and discovered this:
Holy cow, this may have really worked! I was left with a solid disk of gelatin, filled with specks of burnt flour and other assorted gunk. Everything was looking great so far. Now for the true test: Could I cook in it?
I heated up the clarified oil on the stovetop and was alarmed, as it started bubbling a little while heating—an indication that there were still at least a few microscopic droplets of water in the fat—but with a little shaking, the bubbles soon completely dissipated, and the oil continued to heat up just like any fresh oil would. Once it hit the desired temperature, I fried a few pieces of green bean tempura in it, followed by a small batch of fried chicken. Both recipes came out perfect, as if they'd been cooked in not-quite-fresh-but-still-super-clean oil (bear in mind, this oil was on its last legs before I filtered it).
Incredible! Not only did the oil come out cleaner and more usable than it would with any other method I've ever tried, the process was also far easier. Instead of having to clean out a strainer (not a fun task), all I had to do was pop out that disk of hardened gelatin, complete with all the trapped flotsam and jetsam, and toss it in the compost.
Obviously this technique is going to have to be refined and codified for optimizing the gelatin-to-water ratio, the temperature of the water, how vigorously it's mixed into the oil, et cetera, but I'm just so darn excited about the prospects that I couldn't resist sharing it right away.
How to Gelatin-Clarify Oil
- After deep-frying, allow your cooking fat to cool to room temperature or slightly warmer.
- Measure into a small pot half a cup of water for every quart of used oil. Sprinkle it with one teaspoon of powdered gelatin per half cup of water, and let the gelatin hydrate for a few minutes.
- Bring the water to a simmer (you can do this on the stovetop or in the microwave), stirring, until the gelatin dissolves. Stirring vigorously and constantly, pour the gelatin/water mixture into the dirty oil. It should look very cloudy and relatively homogeneous at this stage. Cover the pot and place it in the refrigerator (or transfer the mixture to a separate container before refrigerating), then allow it to rest overnight.
- The next day, pour the oil from the top of the pot or container into a separate clean, dry pot. Discard the disk of gelatin that remains. The clarified oil is ready to use.
N.B.: The first time you use the clarified oil, you'll find that as it heats up, it will start to bubble a little bit. This is okay. Swirl the pan gently as it bubbles to help release any remaining droplets of water. It will eventually settle down until it's ready for frying.