About the author: After graduating from MIT, J. Kenji Lopez-Alt spent many years as a chef, recipe developer, writer, and editor in Boston. He now lives in New York with his wife, where he runs a private chef business, KA Cuisine, and co-writes the blog GoodEater.org about sustainable food enjoyment.
Kenji recreated the steps used by McDonalds® at the factories used to make the frozen French Fries shipped to local franchises and he ran many experiments to control over half a dozen aspects of what makes the perfect fry.
What I have provided immediately below is his recipe for perfect French Fries, and then the gist of the research done by Kenji to illustrate the detail and dedication necessary to create a perfect product. I also provided my own comments in italics. The idea is that you can simply use the recipe and make the fries or if you are interested you can dig into the research detail and really understand what is going on.
Ingredients: (serves four)
2 lbs. of fresh russet potatoes
2 tbsp. of distilled white vinegar
2 tbsp. of Kosher salt
2 quarts of peanut oil
Directions:
Begin the process to heat the peanut oil by putting it into a five quart Dutch oven or into a large wok. Heat it on medium to high heat to a temperature of 400°F while you are doing the other preparations below. Remember to use a candy or frying thermometer to assure accuracy in the oil temperature.
Peel and cut the potatoes into ¼" by ¼" fries putting them into a bowl of water as they are cut.
Drain the water off and place the potatoes and the vinegar in saucepan and add 2 quarts of water and 2 tablespoons of salt.
Bring the mixture to a boil over high heat. Reduce the heat to low and boil gently for ten minutes. After ten minutes the potatoes should be fully tender, but not falling apart.
Drain and spread the potato pieces on a paper towel-lined rimmed baking sheet. Allow the potato pieces to dry for five minutes.
Add 1/3 of the cooled dried potato pieces to the hot oil. The oil temperature should drop to around 360°F.
Cook for only 50 seconds, agitating occasionally with wire mesh spider, then remove the fries to a second paper-towel lined rimmed baking sheet.
Repeat the frying process with the remaining potatoes, in two batches, allowing the oil to return to 400°F before each addition.
Allow all of the fries to cool to room temperature and to drain off any excess oil. Use a third paper-towel lined rimmed baking sheet and transfer the fries to it in a single layer.
Freeze the fries overnight in a deep freeze. At this point the fries can be packaged in a freezer bag and stored for up to two months or they can be used immediately.
As described earlier, heat the peanut oil to 400°F over high heat. Fry half of the frozen potatoes until they are crisp and light golden brown, about 3 1/2 minutes, adjusting the heat as necessary to maintain a temperature of 360°F.
Drain the completed fries and put them into a bowl lined with paper towels. Season them immediately with kosher salt.
The French Fries from this first batch can be kept hot and crisp on a wire rack set on a sheet tray in a 200°F oven while the second batch is being fried.
Serve immediately.
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Background Research:
Below is the research performed by Kenji, preceded by his definitions of the perfect French Fry.
The Anatomy of a Perfect Fry:
There are a few factors that go into making a perfect fry:
Factor #1: The exterior must be very crisp, but not tough.
In order to achieve this crispness, the surface structure of a fry must be riddled with micro-bubbles. It's these tiny crisp bubbles that increase the surface area of the fry, making it extra crunchy. Ideally, this layer should only be as thick as it needs to be to add crispness. Any thicker, and you start running into leathery territory.
Fry Factor #2: The interior must be intact, fluffy, and have a strong potato flavor.
Fries with a pasty, mealy, or gummy interior or even worse, the dreaded state known as "hollow-fry" (when the interior is missing entirely) are an automatic failure.
Fry Factor #3: The fry must be an even, light golden blond
Fries that are dark or spotty have an off-putting burnt flavor that distracts from the potato. Light golden but perfectly crisp is how I want my fries to be.
Fry Factor #4: The fry must stay crisp and tasty for at least as long as it takes to eat a full serving.
All French Fries will become limp after an hour of cooling but done right they will retain their crispness at room temperature for at least fifteen minutes.
Deconstructing the Arches: (Kenji got some frozen fries from McDonalds®)
The first thing I noticed was the surface texture of the fries. They seemed smooth, but on closer inspection, I noticed that they were dotted with very tiny bubbles, indicating that they had definitely been fried at least once prior to arriving at the store. I measured them with calipers and found that they were precisely 1/4 of an inch thick. A good size for optimizing crust to interior ratio.
McDonald's used to fry their potatoes in beef tallow, giving them extra flavor and making them extra crisp, but they stopped doing that years ago. But perhaps there's still something magic about their oil? To test this, I fried a batch of the frozen fries in 375°F peanut oil, letting them cook for about 3 minutes before draining, seasoning, and tasting.
They were just as perfect as the fries at McDonalds®.
That answers the first question. There is no magic in the oil. Something must be done to those potatoes during the pre-processing that makes them unique.
Kenji found an article on the Internet created by a former McDonalds® factory employee that described in detail how raw potatoes are processed prior to shipping them frozen to the various franchise locations.
The cut potato strips are flumed out of the A.D.R. room to the "blancher." The blancher is a large vessel filled with one hundred and seventy degree water. The trip through the blancher takes about fifteen minutes. After the fries leave the blancher, they are dried and then it's off to the "fryer," which is filled with one hundred percent vegetable oil. The oil is heated to three hundred and sixty five degrees and the fries take a fifty second dip before being conveyed to the "de-oiler shaker," where excess oil is removed.
Pre-cooking the fries in a water bath the way McDonalds® does accomplishes two goals. First, it rinses off excess simple sugars, helping the fries attain a light gold color, instead of a deep dark brown. Secondly, it activates an enzyme called pectin methylesterase (PME). According to an article in the Journal of Agricultural and Food Chemistry, PME induces calcium and magnesium to act as a sort of buttress for pectin. They strengthen the pectin's hold on the potato cell's walls, which helps the potatoes stay firmer and more intact when cooked to a higher temperature. That's why the surface of a McDonald's fry looks the way it does: rather than blistering into large bubbles like a traditional double-fried french fry does, the reinforced walls form the super-tiny bubbles that give them their extra crunch.
Not everyone has an easy way of blanching at 170°F, so Kenji thought about boiling the fries to perform the blanching, without causing them to break down or disintegrate.
What if rather than trying to fiddle with temperature, I just relied on the use of acid to help the potatoes keep their structure? I tried bringing two pots of cut potatoes to a boil side by side, the first with plain water, and the second with water spiked with vinegar at a ratio of one tablespoon per quart. Here's what I saw:
The fries boiled in plain water disintegrated, making them nearly impossible to pick up. When I added them to the hot oil, they broke apart even further. On the other hand, those boiled in the vinegared water remained perfectly intact, even after boiling for a full ten minutes. When fried, they had fabulously crisp crusts with tiny, bubbly, blistered surfaces that stayed crisp even when they were completely cool. As for the flavor, if I tasted really hard, I could pick up a faint vinegary undertone, though I wouldn't have if I didn't know it was there. Even knowing it was there, it wasn't unpleasant at all. After all, I'm used to putting my fries in ketchup or mayo, both of which contain plenty of acid.
Getting Inside the Fluffy Interior:
Now that I'd perfected the crust, the final issue to deal with was that of the interior. One last question remained: how to maximize the flavor of the interior. In order to stay fluffy and not gummy, a lot of the interior moisture needs to be expelled in the cooking process, so my goal should be to make this evaporation as easy as possible. I figure that so far, by cooking it all the way to boiling point, I'm doing pretty much the right thing—the more cooked the potatoes are, the more the cell structure breaks down, and the easier it is for water to be expelled. To confirm this, I cooked three batches of potatoes, starting each in a pot of cold, vinegared water, and bringing them up to various final temperature (170°F, 185°F, and 212°F) before draining and double-frying them. Not surprisingly, the boiled potatoes had the best internal structure. Luckily, they were the easiest to make as well.
Freezing Helps with Water Removal in the Final Frying:
But was there anything more I could do? I thought back to those McDonalds® fries and realized a vital step that I had neglected to test: freezing. Every batch of McDonalds® fries is frozen before being shipped out to the stores. I always figured this step was for purely economic reasons, but perhaps there was more to it?
I tried freezing half a batch of fries before frying them and tasted them side-by-side against the other half. Fries and frozen fries, pre-blanched to various temperatures. The improvement was undeniable. The frozen fries had a distinctly fluffier interior, while the unfrozen ones were still ever-so-slightly gummy. It makes perfect sense. Freezing the potatoes causes their moisture to convert to ice, forming sharp, jagged crystals. These crystals damage the cell structure of the potato, making it easier for them to be released once they are heated and convert to steam. The best part? Because freezing actually improves them, I can do the initial blanching and frying steps in large batches, freeze them, and have a constant supply of ready-to-fry potatoes right in my freezer just like Ronald himself!
There you have it … the work of an expert patiently conducting research to create the perfect product.
My thanks go to Kenji! He answered many of my unanswered questions. Even better, I vacuum seal individual serving size amounts of the frozen fries and keep them in the deep freeze and that really maintains high quality for later use ... no oxidation and no freezer burn!