Iain Bagwell
Chef Joe Truex using his Combi Oven to make Japanese souffle cheesecake; Repast, Atlanta, GA
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Ask Dr. Knützenboltz

Chris Styler / May 2010

Dear Dr. K: I've been cooking on the space station for the last decade and I'm a little out of touch. What's all this talk about combi ovens?

A: Combi oven is a generic term for a cooking unit that functions as a convection oven, steamer, or--this is where the "combi" comes in--both at the same time. The technology, in one form or another, has been around for 30 or so years, but combi ovens are finding their way into more kitchens than ever because of chefs' growing awareness of how they work and what they're capable of doing.

The latest generation of combi ovens feature accurate-to-the-degree temperature calibration and cooking programs that can accommodate, in some cases, up to 20 changes in temperature and/or humidity per program. Most combis now come loaded with programs for cooking all the basics from roasted chicken to crusty baguettes (with humidity/temperature settings that can take dough all the way from proofing through baking) as well as the ability to create user-developed programs. In some cases, new or updated programs developed in the manufacturer's test kitchens can be downloaded from a Web site onto a stick drive and then uploaded from oven to oven--useful if you're cooking the same items in four (or 400) locations. Cooking in almost all combi ovens can be temperature-probe driven, i.e. temperature and humidity changes can be triggered when a temperature probe, inserted into the food before cooking, reaches a certain temperature. Additionally, because the inside of the unit is waterproof, cleanup is as simple as a quick hose-down or, in the case with many combi ovens, hitting a preprogrammed "Clean" button.

New features emerge in each generation. Robert Simmelink, executive chef of Alto-Shaam, thinks of the debut of "combi smoking" as his company's single most important innovation. Used with any combination of convection/steam, combi smoking cuts traditional 12-plus hours of smoking time by 75 percent and minimizes shrinkage in the bargain. "In traditional pit barbecue, you have to reach and maintain a temperature and leave a rack of ribs in the pit for up 18 hours," Simmelink explains. "We cook and smoke ribs at 250 degrees in combi mode for one hour and then hold them for another hour. They're fall-off-the-bone tender in two hours. The best part: run the oven through a five-minute clean cycle and all trace of smoke flavor is gone from the cabinet. You're back in business for cooking nonsmoke items without flavor transfer."

In addition to its existing auto-cleaning, Rational has introduced de-scaling and de-liming control to their ovens. A built-in sensor advises when the unit needs de-scaling, and drop-in tablets take care of the problem. According to international marketing manager Vinod Jotwani, this feature eliminates the need for water softener and extends the life of the equipment.

Electrolux looked to the auto industry for inspiration and has been installing Lambda sensors in all of their new units. According to executive chef Sean Lucas, the Lambda sensor "measures humidity and oxygen content in the cabinet and makes adjustments accordingly, using a vent in the top of the cabinet. If I'm cooking chickens, two or 24, the element will sense the humidity in the cabinet. If the humidity coming off the product exceeds what we've set, a vent on top of the oven restores the humidity."

Hobart has taken programming one step further with their Bluetooth-enabled combi oven with bar code scanner. Software that comes along with the combi makes it possible to create cooking programs that are activated when a product's bar code is scanned or to print bar code labels for recipes that are created in-house.

Lastly, while blast-chilling isnt exactly new technology, the number of foodservice operations that are incorporating cook/chill into their routine, whether for HACCP or QC reasons, is on the rise. Manufacturers, such as Electrolux with their Air-O-System and Hobart in conjunction with affiliated company Traulsen, are making it easy to wheel a rack of combi-cooked foods right from the oven and into the chiller.

Dear Dr. K: So what exactly is worth getting so worked up over? Can't I just stick a hotel pan of water in the bottom of my convection oven?

A: Sure you can. Just don't expect the same results that a combi oven delivers. What makes combis so near-miraculous is the precision with which they can be programmed. Not only can chefs program each unit with intervals of dry and steam heat, they can set the amount of steam and temperature during each interval. In short, with some tinkering, you can determine the ultimate setting for whatever you're cooking--from roasted duck to crème brûlée--and "ask" the combi to remember those settings in a program. The combination of convection cooking and humidity control--and the ability to precisely control the amount of steam and the temperature inside the unit--means quicker cooking, less shrinkage, and remarkably consistent results. Lucas cites Electrolux's Air-O-Steam combi ovens as capable of delivering a meager 8 to 10 percent yield loss on large roasts.

As for consistency and accuracy, Alto-Shaam's Simmelink relates this real-world story: At a VIP launch of a restaurant in a major hotel chain, Simmelink and his combi therm produced a main course centered around 800 six-ounce beef fillets, seared first on a grill then finished with combi cooking. "Of course, some fillets were thicker and some thinner," Simmelink recalls. "We cooked them off 400 degrees at a time, with temperature probes inserted into one fillet on each tray, at 135 degrees. They were all cooked to 135 degrees in about 20 minutes. We served 800 steaks in two rounds with exactly eight returns."

This fine-tuned precision is especially helpful at the low end of the temperature scale, when regular ovens--even well-calibrated ones--tend to slip up.

Dear Dr. K: What's the big deal about low temp?

A: Two big deals, really, plus a few smaller deals. The first is the ability to cook with steam at a reduced temperature, which yields more delicate results. Seth Greenburg, executive chef of The Huntley hotel in Santa Monica (and just about every other chef who has experience with combi ovens), cites delicate crème brûlées that emerge evenly cooked, without a speck of brown and nary a surface bubble--all without the hassle of a water bath. Joe Truex, chef/owner along with his wife, chef Mihoko Obunai-Truex, of Repast in Atlanta, uses his Rational SelfCooking Center to prepare many of the restaurant's Asian-influenced dishes, including a steamed Japanese soufflé cheesecake, which is cooked in steam mode at 170˚F. "I can't reproduce this dessert in a regular steamer," Truex cites. "The lower temperature means gentler cooking and a very light result, not just for the cheesecake but other desserts as well. I don't believe in inducing food coma; I believe in balance."

The second big deal is how combi ovens simplify two of the last decade's major cooking trends: sous-vide and fat-poaching. "Low-temp cooking is one of the things that people may not think of first when they think of combi ovens", says Simmelink, who claims that low temp is where combis really shine. "Anything you can cook sous-vide you can cook in a combi oven," he states, including vegetables, starches, and every protein from the now-classic sous-vide 72-hour short rib to eggs poached in the shell. (For the latter, eggs in their shells are placed in a perforated pan and cooked in combi mode at 148°F for 40 minutes, then blast-chilled. After retherming in combi mode at 275˚F for four minutes, the eggs are ready for cracking right onto toasted English muffins.)

Greenburg stands the sous-vide process somewhat on its head, starting with proteins cooked in a combi and ending up with them sealed in bags, ready for service. "I think of my combi as a big sous-vide cooker--after all, the seal is airtight," Greenburg states. For the hotel's banquets he slow-cooks short ribs, for example, in perforated hotel pans with a drip pan under all of them to catch the juices. The ribs are removed and seared on a plancha for flavor and color and the collected juices are used to build a sauce. Once the components are ready, Greenburg packs them up in sous-vide bags, adds the sauce and, when the time comes, retherms them on the service line in immersion circulators.

Another low-heat trend--poaching proteins in olive oil or butter--seems to be what combi ovens were invented for. "Any seafood that is done stovetop can be done in a combi oven," says Simmelink. "If we're cooking lobster, for example, and want the lobster to hit 158 degrees, we run the oven on convection mode at 163 degrees and put the butter in a hotel pan for 20 minutes or so to melt. Then, in goes the lobster and using a sous-vide temperature probe, which is smaller than a regular probe, we record internal temp and pull it at 158 degrees."

Simmelink points to a few other not-so-apparent uses for low-temp steam: canning, working with agar-agar, and tempering chocolate. The last is a task well-suited to the combi oven's finely tuned temperature calibration. Canning, which can tie up the stove with huge pots of boiling water, is done in a combi oven simply by putting the filled jars on a sheet pan and steaming at 186˚F for approximately 15 minutes (depending on the size of the containers and temperature of the food when it is put into the containers) to achieve a perfect seal. In a recent round of tests, Simmelink fashioned a lobster terrine made with agar-agar dissolved in celery and grapefruit juices. Once chilled, the terrine was sliced and rewarmed in convection mode at 150˚F. "Agar-agar works like gelatin, but you can heat it to 185 degrees," Simmelink explains. "At 150 degrees the agar-agar held, and the color of the celery and grapefruit juices stayed nice and clean."

Sounds complicated. Do I need a B.S. in combi ovens?

A: Like all new equipment or techniques, there is a learning curve involved. But most chefs agree: the time you put into learning to operate the oven and the time spent honing your cooking programs is more than repaid with radically shortened cooking times, less yield loss, and consistency. If you do need a hand, most manufacturers are more than happy to send representatives to help with the basics of programming. Most, like Rational, offer support during the presale phase when sales rep/chefs do a test-drive with interested chefs at 150 locations throughout the United States. "We encourage chefs to visit our training locations and to bring some of the items on their current menu so we can compare what they're making with their own equipment," says Rational's Jotwani. "Beats the heck out of a brochure."

Electrolux offers similar pre- and post-sales support. In fact, one of Lucas' main responsibilities is matching up combi oven newbies with one of the company's regional chefs. "It works well--our chef works with our oven in the real environment, with the chef's team and the actual items and ingredients from the menu."

The social networking craze has extended to the world of combi cooking: each of Alto-Shaam's chefs has a Facebook page to answer users' questions and to post new ideas, and how-to videos are posted regularly on YouTube (search "justshaamit").

Dear Dr. K: My kitchen is already loaded to the brim with equipment. Do I really have room for one of these things?

A: The question most combi-savvy chefs would ask is, "Do you really not have room for a combi oven?" A combi can, in a scaled-down footprint, roast beautifully, braise overnight ("It cooks while I sleep," Truex says happily), steam, dehydrate, produce desserts with minimal hassle and retherm sous-vide or even plated dishes. One or more can be an ideal way to reduce clutter in the kitchen and streamline operations. Ask Greenburg, who relies on a pair of Alto-Shaam ovens for virtually the entire output of his tiny, remote-from-the-main-kitchen, banquet and pastry kitchen. The ovens, which feature an optional self-venting attachment, need not be situated under a ventilation hood, another feature which nudged Greenburg toward his decision to go combi. "That kitchen is tiny, but since we bought those ovens, it's pretty much the two combi ovens and a bunch of counter space."

Truex, who uses two of Rational's SelfCooking Center's smallest tabletop model (the ‘61'), stacked one atop the other, makes his case for the switch: "For the footprint of the thing, it does an amazing amount of work. I've had to rethink the way I cook--in a good way." Truex sears meats for braises at high heat in combi mode ("a beautiful crust," he notes), then continues the braise by adding liquid and cooking at 300˚F in combi mode. "No more standing over a rondeau while the meat is browning." To deal with the seasonal vegetables that flood Repast's kitchen, Truex eschews huge pots of boiling water and chooses instead to steam them in perforated pans at 265˚F, then top-ices them and douses them with cold water (that waterproof lining again!). "Blanching all the vegetables in the combi oven saves a huge amount of time and space. I can chill them instantly, and the drain is right there. It's less work for the dishwasher, less time and stove space for me."

Combi ovens can, with some items, act as a holding unit as well. Greenburg has cooked six 18-pound turkeys in a little over an hour and a half to golden brown perfection and held some of them for up to four hours with virtually no adverse affect on juiciness or flavor. Electrolux's Lucas cites another advantage of holding time. "When beef is roasted, then held in this kind of controlled environment, the enzyme breakdown is similar to what happens when beef is dry aged," he explains. "One hour of holding time is the equivalent of two days of aging hanging beef. So I can set the oven when I leave at night and come back to perfectly roasted, extremely tender beef."

All right, Dr. K: This all sounds fine, but the bottom line is: I got into this biz to cook, not to push buttons.

A: Greenburg feels the same way. After initial resistance to the technology, he has come to rely on his combi ovens and see them for what they are: the next step in the evolution of cooking. "You still need to watch everything that comes out of your combis," he cautions. Greenburg, who is using his combi to develop a fat-free french fry ("not perfect, but we're getting there…"), doesn't see combi cooking as a surrender. "You still have to poke, test, and use your judgment," he reasons. "But what I've found is that these ovens are incredibly reliable, and the time they save me I devote to creating new dishes," And isn't that what it's all about?