Illustration by Emily Torem
American disposable food culture notwithstanding, a restaurant is about more than efficiently transferring food from a refrigerator to a stomach. The best restaurants create a sense of place—through the food preparation, the physical surroundings, the textures and the temperatures—that make diners feel at home and nurture our humanity.
At the root of the dining experience, whether it’s clinking coffee mugs over Western omelets or brushing crumbs off a silk tablecloth, is the discovery that made humanity, well, human: fire. In the following, we’ll be exploring how man has enhanced, controlled and directed heat to cook his food and warm his hearth at various points throughout human history.
COOKING WITH (CONTROLLED) FIRE
India: The Good Earth: how clay, cob and soil make everything from ovens to homes
Though it was discovered as early as 3000 BC in the Indus Valley Civilization, the tandoor, a fired-clay oven known for its present day use in India, still turns out a superior skewer of chicken and garlic-y flatbread to the conventional oven, which only hit the scene in the 1830s. The unique shape of the tandoor, like a giant, curving clay vase with an open top, allows for skewers of meat and fish to be inserted vertically into its cavity, and Naan to be simply slapped along its scorching hot sides, which can reach upwards of 900 F. The bottom of a tandoor is coated with coals, which burn to embers before cooking to ensure even exposure to the heat. The clay reflects heat back onto the meat, while the metal skewers, introduced by Pakistan years ago, draw heat from the fiery coals at the bottom, and cook proteins evenly from the inside out. Often herbs are tossed onto the embers, so their scent is infused into the smoke for a subtle boost in flavor.
Today, Tandoors are either built into the earth, or into what look like metal work tables (more common in restaurants). Tandoors are also important fixtures in the traditional cuisines of Georgia and Armenia, going by the names “tone” and “tonir” respectively. Traditionally made of local and regional clay, composition of the tandoor can change by region, but no matter the classification, these natural ovens can last a very long time.
Tandoori ovens aren’t the only structures taking advantage of the wonderful durability of local clay and earth. Cob—a combination of sand, straw and clay— is a growing presence in the sustainable design community. This building material is infinitely versatile, biodegradable, non-toxic, and can be found most anywhere. Best of all, the slick, sultry combination of earthen materials hardens into an impermeable, strong and moisture-free enclosure once treated and fully dry.
Cob for use in Restaurant Construction
Cob can be used to build anything from passive solar houses to outdoor pizza ovens (that can also handle the likes of vegetables and meats—you just need to install a solid door). Resourceful Chicago artisan Anna Wolfson who created the plaster barrel-vaulted ceiling on our Bar Pastoral restaurant design, has made several cob ovens including one in her backyard at her current apartment. Like the culture of the Indian Tandoor, where village women would gather for hours around the oven, cooking bread and catching up, outdoor cob ovens bring a greater social element to the cooking experience, widening the circle beyond four walls. “[When] we make pizza, the neighbors come and start hanging out, so it’s really [a lot more social] than cooking in the kitchen,” says Wolfson.
Wolfson says that living in Chicago, especially as a renter, it can be hard to incorporate natural building techniques into everyday life, despite cost not being so much an of an issue (a cob house can be achieved for as little as $50,000), but a cob oven is […] “a great, bite sized project using actual materials; it’s great for an urban environment.”
Cob as a Locally Sourced Building Material
Cob aficionados take great pride in being able to source materials locally, something moss also emphasizes in our architecture. We sift through salvaged and reclaimed fixtures and materials at the Rebuilding Exchange, and seeing what we can conserve from the residence we are rehabbing (sometimes the gnarliest looking drywall can be hiding the most beautiful masonry). Wolfson echoes this local approach, even looking in her own backyard for materials. “I wanted [the oven] to be really tall, and our neighbor’s whole backyard was paved, [so] they broke up the pavement, which we used to help get the height,” Wolfson recalls. “[Then] we infilled that whole thing with their recycling: glass bottles and leftover bags of clay.” She proudly adds “it’s like a little landfill.”
Often with cob projects, all the materials you will need are right beneath your feet. Because of its pliability when wet, cob walls can be matched to salvaged windows and doors, and shelves can be built right into the interior walls, saving on energy expenditure and conserving our natural resources. For this oven, Wolfson used corrugated metal and round wood salvaged from the scrap yard.
The interplay of thermodynamics and natural materials is one of the most fascinating parts of working with cob, clay and earth. “The clay and the sand on the inner layer of the oven absorb heat from the fire, and then through convection, they re-emanate it back into the oven,” Wolfson explains. The outer layer, made of clay and straw acts as an insulator. “The straw is tubes of air, which blocks the loss of heat,” she continues. The firebrick on the oven’s floor is brick that has been fired at a really high temperature, so it can withstand the heat of the oven. However for all of cob’s magical powers, it is still a natural material, liable to breaking down if it isn’t protected properly. “Anything that is a natural material needs boots and a hat,” Wolfson says. This could be a concrete or gravel foundation, and a strong roof. But with proper care, cob ovens and other structures will be functional for years to come. “[There’s] one we built about six years ago, and it’s still firing like a champ. Cracks form, [but] you just have to integrate that into your sense of aesthetic beauty.”
Hawai’i: The thermal mass of stones keeps meals hot and dwellings comfortable
To cook a very large pig for a Lu’au in the traditional Imu—a Hawaiian earth oven stuffed with volcanic stones—begin the night before. A pit 2-4 feet deep is dug deep into the earth, and at its bottom, a blanket of kindling is set ablaze. Cover the fire with vesicular basalt stones, the ones with little holes, which much like a puncturing of a baked potato, will keep the rocks from exploding as the heat climbs. Once they are white hot, after about 1.5-2 hours, set some aside—you’ll need these to stuff inside your Lu’au pig, aiding in even cooking from the inside out. The pig (kalua) is then sandwiched between two layers of damp vegetation such as banana stalks, or even corn husks for those of us outside of the tropics. Cover the whole thing with a tarp and then wait 7-9 hours before unveiling your present: perfectly tender, steam cooked pork, enough to fund a party into the early morning light.
Although cooking with rocks may conjure up the folk tale of stone soup to the uninitiated, hot stones make excellent aids in thoroughly cooking meat and fish because of their fantastic thermal mass properties. Objects with high thermal mass not only absorb heat from the sun and hold onto it, but release it when the ambient temperature around them grows relatively cooler (the second law of thermodynamics states that heat flows from hot environments to colder ones). So, you stick a cold piece of meat on a blazing hot rock, and voila, a pound of ground chuck becomes a burger.
Thermal Mass in World Food Culture
Hawai’i isn’t the only place in the world to use the thermal mass of rocks to its advantage. In German culture, New Year’s festivities find home cooks relieved of their kitchen duties when something called Der Heisser Stein (“The Grilling Stone”) is brought out to the dining table. After leaving this slab of granite in an oven for several hours, it’s stored enough heat to cook the celebratory feast while the host/hostess gets to enjoy the company of their friends and family. At Hot Stone Cafe in Siem Reap, Cambodia, volcanic stones heated to 400 F are brought out to tables so patrons can watch their meals cook themselves as shown below.
Thermal Mass in Building Construction
From a passive solar design/permaculture perspective, stones and their high thermal mass quotient are indispensable as a building material. We spoke with Kelly Hart, writer and founder at Green Home Building, and builder of his own passive design house to find out why.
“Thermal mass is a kind of heat battery that stores warmth, absorbing it to keep the room from getting too hot during the day…[and giving it] back into the room when the sun goes down,” says Hart. “Stone can greatly reduce the need for mechanical heating inputs or eliminate them altogether.”
The principle of thermal mass works exactly the same way for the Hawaiian Lu’au as it does for a passive solar home; heat is absorbed into a solid mass in an enclosed space and then that heat is re-radiated back into the space over an extended period of time. The benefits of good passive home design are numerous to both homeowners and the environment: save on energy bills, cut down on carbon emissions, and enjoy a more consistent temperature throughout the home. And all that from an inconspicuous old stone! So there you have it: the power of stones to cook a whole pig, and regulate indoor temperature without a thermostat.
Traditional Korean In-Floor Heat
Used in Korea since the Bronze age, the word “Ondol” literally means “warm stone”, and refers to the layer of flat stones underneath the floor, which are heated from below by a traveling fire. Unlike the Roman Hypocaust, a similar underfloor heating method, but which carried the risk of Carbon Monoxide, Ondol draws its heat from the family’s hearth, putting the warmth generated by nightly dinner prep to good use.
As mentioned, Hypocaust-style heating was dangerous, because of the open flame. To avoid the dangers of Hypocaust-style open flame heat, the Koreans separated the flame of the fire from its smoke. Ondol flames travelled horizontally, through a series of flues, which terminated in a chimney for smoke to escape at the other end of the house. By having a flue entry located beside the furnace, they prevented the smoke from traveling upward, so it stayed warming the floors for as long as possible. Koreans also harnessed the power of smoke to their benefit. Traditional Korean houses were mainly constructed with wood, making them vulnerable to pests, bacteria and mold. Smoke, with its natural sanitizing qualities was the perfect solution, wiping out troublesome insects as it traveled through the flues.
Today, the mechanics of Ondol are still the same, but instead of fire doing the heating, hot water from showering and cooking is channeled through pipes that warm the floors above. After being thoroughly impressed by a traditional Ondol room in Japan, architect Frank Lloyd Wright imported this updated Ondol technology stateside in the 1930’s. He designed many of his buildings, including the below pictured L-shaped Herbert Jacobs house, to incorporate underfloor heating, via hot water pipes. Currently known as Radiant Floor Heating (RFH) in the U.S., Ondol has come a long way from its Bronze Age roots, and is an increasingly viable alternative for homes looking to minimize energy costs.
Radiant Floor Heating in Modern Design
Although it’s not easy to install RFH in an already existing structure, when adding a new room or project from the ground up, this type of heating, which can use hot water or electricity, is more energy efficient than the common HVAC. Just think about it; when hot air is blown downwards out of a vent, it immediately wants to rise back up to ceiling, due to thermodynamics. It then has to drop in temperature in order to fall and blanket the rest of the room (resulting in cold feet syndrome, especially in ground floor apartments). If the heat comes from the floor, it passes through objects in the room as it rises, so they store some of its temperature and then radiate it back out of the room when ambient temperature drops—making use of the thermal mass of inert objects. Bonus points if there are objects in the room with high thermal mass, like stone floors, furniture or earth/mud walls etc.
The prevalence of underfloor heating, from the traditional Ondol to the modern day, was instrumental in creating a culture that made floors the central domestic space. To wit, the first thing you do when you enter Korean homes is take off your shoes. This isn’t just a cultural custom, it’s because people eat and sleep on the floor and they don’t want whatever gross thing you stepped in tracked in from the outdoors. Traditional Korean beds are mats, keeping minimal space between body and warm, cozy floor. In contrast, Western-style beds, tables and chairs are quite high, putting ample space between human and cold, drafty floor, allowing warmer air (relative to the floor) to act as an insulator. Until about 30 years ago, most Koreans were still sleeping on the floor, though now this custom is mainly practiced by the elderly. Tables are much lower to the ground because folks usually sit on the floor to enjoy their meal, and in fact, spots nearest the furnace in a Korean home are generally reserved for elderly or honored guests as a sign of respect.
Bringing Traditional Design to Hangawi Restaurant
In some North American Korean restaurants today you can still find low tables, cushions and underfloor heating to enjoy a more authentic experience. One such restaurant is Hangawi in NYC, which provides low tables flanked by beautiful cushions that guests sit on to enjoy their meal. Shoe removal is required at the front door, and during the winter, the floors are heated by an electrically powered Ondol to keep customer’s feet warm. We spoke with Manager Terri Choi about how keeping the seating traditional at this Vegetarian Korean restaurant was influenced by her own childhood in Korea, and is a huge part of the dining experience for guests from all backgrounds today.
“When we first started our restaurant, many of our customers were surprised by the idea of taking off their shoes and sitting on cushions on the floor,” recalls Choi. “But over time, this practice has become a big part of our unique experience, where our guests feel as if they have been transported to a faraway temple or retreat in Korea.” The cushion seating exemplifies the Zen aesthetic the Hangawi design team envisioned for the space. “[We wanted it to] evoke an experience of all the senses in total harmony. Vegetarian meals; presentation of traditional teas; folk and zen music [and] decor filled with natural artifacts.”
Growing up in Korea, Choi slept, sat and ate on the floor. “All our extended family members gathered on special occasions like New Year’s Day and Full Moon Day and sat on cushions on the floor facing a long table with food.” Still, she considered her audience when starting her restaurant in New York. Realizing most Westerners weren’t accustomed to sitting cross-legged for an extended period of time, Choi elected to build a well underneath Hangawi’s low tables to allow guests to fully extend their legs
Choi is a big advocate of the traditional cushion style seating, for influencing everything from taste and presence, to bonding with family and friends. “I think sitting lower to the ground helps in mindful eating; It helps you to focus on your food: the taste; the presentation; the fragrance of the dish that is placed before you,” explains Choi. “It also provides a more intimate and bonding experience with your co-diners. It feels more comfortable and relaxing and therefore helps in creating a more informal communication atmosphere.”
How wonderful it is that everything in the restaurant experience, from the chairs we sit on to our dinner table chatter to the char on the bread we break is living history, inseparable from thousands of years of playing with fire. And you thought it was just pizza!