This is the second installment in a series of posts I’m writing on my experience staging at a few restaurants in Southeast Asia. Last time, I talked about the technical similarities between French dough lamination and flaky Asian pastries. Below, I focus on a different doppelganger, this one embraced around the world.
The restaurants I chose to stage at in Asia were all cherry-picked off of the San Pellegrino 50 Best list. They were all modernist, tasting-menu only establishments with exorbitant food costs, expensive gadgets, and dewars upon dewars of liquid nitrogen. And while I learned quite a bit in those kitchens, the truly eye-opening moments came from walking around local markets and tasting foods from vendors for which I had absolutely no point of reference.
One of the dishes that appeared again and again in Thailand, at food carts and in restaurants, in shopping malls and served from disposable trays on the back of pickup trucks, was gluay cheum. Deceptively simple, the dessert is nothing more than cooked bananas served with salted coconut cream. The bananas, however, have a texture unlike anything I’ve ever experienced, completely firm on the outside but with a custardy interior. Achieving this result, it turns out, relies on an Aztec technique developed in 1200 BC.
Nixtamalization, which is the Nahuatl word for steeping field corn in alkaline water before cooking, is a process most cooks are marginally familiar with. Without it, they know that grinding corn into masa (which is then used to make tortillas and tamales) is backbreaking work, and they probably have eaten un-ground nixtamilized corn, known as hominy and a main ingredient in pozole. Less obvious is how the science behind nixtamalization has been applied to other foods around the world, everywhere from Brazil to Malaysia.
Warning: this post is going to get nerdy for a hot second. The technique behind making masa relies on calcium oxide that is mixed with water to make calcium hydroxide—Ca(OH)2—which is also commonly known as cal, quicklime, pickling lime, slaked lime, and red lime. A fine white powder, calcium oxide is made by heating limestone or seashells that contain calcium carbonate to extremely high temperatures (around 1520 degrees Fahrenheit). Dissolving the powder in water is referred to as “slaking.” With a saturation point of about 1.5 g per 1 L of water, most recipes call for 1 teaspoon of quicklime to be dissolved into 1 gallon of water. As long as one doesn’t go above the saturation point, the quicklime with stay suspended in the water, with the exception of Asian red lime. Throughout Southeast Asia it is common for the powder to be mixed with a little water and turmeric into a paste, solid in jars, and intended to diluted with more water and left to sit overnight before use, during which time some of the turmeric will settle out and color the liquid a bright pink. (There’s even a Thai expression “ขมิ้นกับปูน” that literally means “turmeric and lime,” but is used as slang for people that simply cannot get along or are incompatible, referring to the natural separation that occurs in water.)
Okay, science is out of the way. tl;dr – chemistry is fun!
In masa making, the corn is soaked in the alkaline (basic, pH above 7.0) water to dissolve the pericarp (really hard outer skin), which allows each grain to swell with water and grind more easily. As long as the soaked corn isn’t rinsed too much, the pericarp will remain in the mixture, and once ground forms a mass of gummy polysaccharides that acts like a hydrocolloid and binds the masa together. A convenient side effect of soaking the corn in CALCIUM hydroxide is that each kernel absorbs calcium from the solution, which enables products made with masa to act as the primary source of calcium in one’s diet. So the gist is: limestone à heat à alkaline water à corn à tortilla. A very useful and specific application of Ca(OH)2.
A few thousand years later and half a world away, Thais began using the same process on small burro bananas (about half the size of regular Cavendish bananas) that you’ve probably seen in Asian markets. Sliced and soaked in an identical quicklime solution, the intent here is not to break down the outside of the fruit (like the corn) but to strengthen it. Bananas naturally contain pectin, and the calcium in the water cross-links with the pectin (cross-link sounds technical, but you’re definitely familiar with it vis-à-vis glutenin and gliadin forming gluten, or sodium alginate and calcium chloride making neat spheres in fancy kitchens) to form a very thin “skin” around the banana. The Thais then lightly rinse the banana pieces and cook for two to three hours in a sugar syrup. Because of that “skin,” the outside of the banana remains firm, as if it were raw, while the inside is cooked in the hot liquid. Result shown below.
And while a timeline of when certain cultures adopted this practice isn’t traceable, the same technique is used throughout South America on pieces of pumpkin and squash. It has even made its way stateside, employed at Cosme in New York City on papaya for a dessert.
Another common sight across Thailand is street vendors selling chunks of fried banana and taro. Slightly bumpy from the inclusion of sesame seeds and grated coconut, the batter is a combination of water, rice flour, sugar, and quicklime. Here, the alkalinity does two things: first, it creates a deep golden brown exterior by speeding up the Maillard reaction in the oil, and second, it utilizes that calcium/pectin cross-link to adhere the batter to the banana. Unlike a tempura or fritter batter that might contain baking powder or soda and puffs away from the product when fried, this alkaline kluay khaek batter bonds to its subject. The result is a product that can be fried in the morning and remain crispy for hours, even when held outside in the sweltering 100% humidity found throughout Thailand.
Whether used commercially for turning cucumbers into pickles that stay crunchy on store shelves, making Chinese century eggs, or crafting the ideal tender-yet-chewy ramen noodle, alkaline water made with calcium oxide is an endlessly versatile tool. To bring my experience in Asia full circle, I recently workshopped a fine-dining example of quicklime in action, using it to tenderize bananas before dipping them in Valrhona’s dulcey chocolate. Yay, science!