Culinary Experiments – Page 2

Four Burgers opened up just a month ago in Central Square with the mission of serving high quality, simply prepared burgers and fries. In this modern era of eco-friendly dining, they do the right thing by composting, recycling, and serving ingredients with known provenance. The net result, for the most part, is fabulous: Juicy, meaty burgers with flavorful toppings and fries that taste like potatoes.

There’s been a small hiccup in the business—and that has been the sweet potato fries. While most would agree that anything fried and salted is better, these fries suffer in that they never get really crispy. Short of coating them with a non-organic/unnatural substance (as many lesser burger joints do), the options are somewhat limited.

The composition of the sweet potatoes creates a layered challenge with sugar, starch and water issues at play. Food science research leaves a gaping hole in this domain.

For regular potatoes, culinary experiments have yielded the best technique… first soaking the potatoes in water to rinse some of the excess starch, cooking the potatoes a first time in 325F oil and then a second cooking in 375F oil to crisp them. Intermediate refrigeration between frying further alters the starches which better enables a crispy fry. Researchers have discovered that Idaho potatoes are the best variety, and farmers have refined the genetics to consistently produce a fail-safe potato.

What works for regular fried potatoes does not translate to sweet potatoes because of the starch, sugar and water content.

And while there are a few sweet potato varieties out there (White Hamon) that are better suited, they are not mass marketed, leaving the small restaurateur to experiment with the readily available varieties.

The starch issue is a complicated one… And after researching in Harold McGee’s On Food and Cooking, I discover this is more complicated than I can address with chain starches and branch starches and the chemical reactions of both. The water and sugar contents pose a more straight-forward challenge. As we know, moisture is the enemy of crispy [[Think about meringues on a humid day or fried eggplant]].

In order to get “watery” foods crispy, we must first batter them to prevent the moisture from seeping out and soggying the crust. Sweet potatoes get crispy in tempura batter because they are sufficiently coated.

Alternatively, in the case of regular potatoes, the minimal water evaporates before the fry crisps up – creating a fry with long-lasting crispiness.

This is when the challenge of the sugar content kicks in: Sugar begins to caramelize about at 334F and starts turning bitter at 363F. This narrow window limits the opportunity for the sweet potato fry to rid itself of excess moisture and get crispy.

Armed with this (somewhat limited) knowledge base, Michael B. (owner of Four Burgers) and I got to work.

Our baseline was a sweet potato fry that was cooked in 350F oil until golden brown and soft in the middle. The fry was mildly crispy straight out of the oil, but quickly turned limp.

The first wave of experiments involved coating the raw fries with a type of starch that would help absorb moisture and increase the starches that would crispy up the fries. We tried corn, wheat and potato starches. And with a nod to the tempura batter, we also made a mix of corn and wheat flours. The best yield was the corn starch. Straight out of the fryer, the potato was crispier than the original, but soon met a similar fate of limpness – though the crisp to limp time gap was greater.

Other starches provided minimal improvement. The biggest complaint was that the floury coating took away from the flavor and “Mouth feel” of the potatoes.

The second round of experiments involved drying the potato first before frying. First, we “par-” fried the potatoes the way regular fries are. This seemed to produce a crispy fry but we soon realized that this extra step was minimal better than the baseline, and not worth the effort.

Par-Baking the potatoes yielded the best result. The potatoes dried out with a gentle heat. Unlike the fryer, the drying process did not brown (i.e. caramelize the sugars in) the potatoes. By the time we put them in the fryer, they crisped up quickly and stayed crispy.

Special thanks to Michael B. and his staff for allowing me to play in their kitchen! Stop by, have a burger and fries and let me know what you think!

I probably like a good burger more than the average person. With proper cooking and simple seasoning, little else is needed to achieve burger nirvana. You can imagine my excitement when Four Burgers opened in Central Square.

The name suggested a simplicity to the offerings, which could either be very good (a juicy burger with a salty, meaty flavor), or very bad (that would require a post-cooking bath in ketchup and salt to make up for where the kitchen failed). The menu lets you know that the meat is of high quality – purchased from the same farm as Grill 23.

In the back of the dining room are bins labeled from composting and recycling. Even with a friendly price point ($6.50 per burger, $10 average check with fries and a drink), you know that this will be a fresh, high quality experience.

The four burgers: salmon, beef, veggie or turkey, come on either whole wheat or white buns. The beef is a classic – no fancy condiments, just simple pickles, lettuce and tomatoes. The romaine lettuce is shredded so it fits nicely inside the bun, without over-expanding the sandwich which would have made the burger difficult to eat. The burger was cooked perfectly to our specifications, which sadly is a rare feat for most joints.

The turkey plays off the traditional Thanksgiving (autumnal flavors). Apple bits are folded into the meat, yielding a slightly sweet and crunchy texture. The burger was cooked perfectly – 95% on the grill, 5% from residual heat – the patty was moist and tender. The apple bits would have compensated well if the burger was overcooked, but oddly, in this case it was superfluous. The cranberry chutney was bright and was a nice diversion from the standard ketchup. My only complaint was that as we head into the heat of summer – I want to think of summer flavors and would have preferred a more seasonal flavor.

The sweet potato French fries posed an interesting culinary challenge. While they tasted like sweet potatoes with a lovely enhancement of salt, they were a bit limp. In speaking with the owner (Michael B. of Paramount and 21^st Amendment fame) he agreed. He noted that the only crispy sweet potato fries come frozen from Sysco and are sprayed with some food-like substance. If you go naturally, as Four Burgers does, the fries won’t get that fast-food crispy.

Four Burgers is not alone in its quest to naturally achieve crispy sweet potato fries. A little research shows that no one has yet to find a solution (and publish it on-line). In thinking about the problem… regular French fries typically use Idaho potatoes – a high starch, low protein, and lower water tuber. You never see Yukon gold fries, and certainly not red bliss. The starch content is low (which has its benefits for other preparations…) but does not yield a crispy fry. What makes the potato oxidize quickly also produces a crispy fry. (also thinking about potato latkes, they get crispiest when you squeeze all the water out of them)
Michael B. and I decided to do a little experimenting in the kitchen. With a nod to Chinese cooking, we tossed the sweet potatoes in a dusting of corn-starch. They fries stayed crisp longer, but soon met the same limpy fate of the original batch. I think we were on the right track, and I bet potato starch would be worth a try. In thinking of the crisp tempura batter, a blend of flours – in that case corn starch and wheat flour, might also work. For sure, you'll find me back there again. But I might wander back into the kitchen to play around with sweet potato fries in a quest to perfect burger nirvana. Stay tuned for more culinary experimentations…

Category: Culinary Experiments

Adventures in Sweet Potatoes

Four Burgers