All Steamed Up
Nils Norén, David Arnold / September 2010
Some speculate that steaming is the oldest cooking technique, carried out over hot springs, and although there's no way to know if this theory is true, steaming has been around for a very long time: Some of the oldest cookware for steaming, stoneware found in the Yunnan province in China, dates from 3000 B.C. And every culture has its own longstanding steamed delicacies: French dishes en papillote, North African couscous, Hawaiian poi, New England clambakes.
Steaming has surged in popularity recently. It is seen as a healthy, easy, fast way to cook and reheat foods--in large quantities, and even from a completely frozen state--with minimal degradation. Certain foods must be steamed to be at their best. Only steaming produces the right texture on a Shanghai soup dumpling, for example; boiled, it wouldn't have that textural stickiness and would probably break apart.
Even beyond these benefits, steaming is seen as an economically and ecologically sound way to cook. Commercial steamer technology has leaped forward in the past 15 years. Modern units can cook large amounts of food using minimal energy, minimal water, and minimal venting--obvious pluses in today's era of expensive utilities and environmental consciousness.
How does steaming actually work? Let's look at some steaming basics:
Steaming is often viewed as an alternative to boiling. How do they compare? Boiling water stays at a constant temperature: 212°F at normal atmospheric pressure. Even if you turn your burner all the way up, the water temperature never increases. So where does all the extra energy go? It's used to turn the water into steam (the technical term for that energy is the "latent heat of vaporization"), and the steam stores that energy. It's a lot of energy: 1 gram of steam has enough energy to raise 7 grams of water from room temperature to boiling. When steam condenses back into water on the cooler surface of food, it gives that energy back, quickly heating the food surface. This is why steam can burn your skin badly and quickly.
On the other hand, steam isn't very dense--in fact, it's over 1,600 times less dense than water--and, as soon as the surface of the food reaches the same temperature as the steam, you no longer get the huge benefit from condensation. At that point, boiling water, with its greater density, becomes the faster cooker. So, thinner items that have a lot of surface area--snow peas or rice--are heated very quickly by steam, whereas thick items--big hunks of meat--are heated faster by boiling.
Steaming is also preferred for cooking food in large quantities, simply because of the energy issue: bringing gallons of water to a boil is time-consuming and energy intensive, whereas steaming large quantities of food requires little water and a short heating time. And while boiling can leach out vitamins, nutrients, and even flavor, steaming won't.
Is steaming gentle? Steam isn't gentle unless you compare it to boiling and deep-fat frying. Most old-school steaming recipes viciously overcook meats and seafood. Many cooks mistakenly believe that delicate foods, including meat and fish, won't dry out in a steamer. Wrong. A piece of fish overcooked in a steamer won't get brown and desiccated as it would in an oven but it will still taste dry. Properly steaming fish is a difficult task. On the other hand, foods that are naturally cooked to high internal temperatures (well-done), like tough braising cuts of meat and thick vegetables, are much harder to abuse in a steamer than in an oven. Some foods even benefit from the high temperatures and fast cooking afforded by steam. Green vegetables are obvious steaming candidates; cooking them quickly helps maintain their color.
Is steaming super healthy? Steaming is often considered the healthiest cooking method. Most data, however, only compares steaming with boiling. We haven't found any data on vitamin retention in steam cooking versus other techniques, such as roasting or cooking in a vacuum pouch. Compared with boiling, steaming leaches out fewer water-soluble nutrients, such as vitamins B and C, minerals, and fibers. The reason is simple: steaming doesn't immerse the food in water. In fact, when boiling, the less cooking water you use the more nutrients vegetables will retain.
We've looked at steam, how about steamers?
Stovetop steaming Stovetop steaming, while limited in the amount of food it can produce, still has a place in the modern restaurant kitchen. Traditional steaming can be done in any pot with a tight-fitting lid and a trivet or steamer insert in the bottom to keep the food from touching the water. If the lid doesn't fit well, too much steam escapes and foods don't cook properly. The disadvantage of this setup is simply the pain (literally) of loading and unloading the pot around the hot steam. Steamer baskets, either stainless-steel or bamboo, alleviate this problem and can double as presentation pieces. These baskets are also ideal for foods that need to be handled delicately.
Traditionally, steamer baskets were used inside a wok. The sloping sides of the wok allow almost any size steamer basket to form a good seal, so steam is sure to be directed through the steamer and not around it. Traditional wok burners are also very powerful, which means you can start steaming quickly after you put the pan on the burner. Most of us don't have access to a wok burner, so when using a steamer basket in a regular pan with sloping sides make sure the basket fits the pan properly; if the steamer rests in the bottom, or sits on top of the pan, without forming a good seal, you won't be cooking efficiently. Even though steamer baskets are made to stack on top of one another, resist the temptation to stack them unless the product in the bottom basket can withstand a lot of overcooking. In a test of four stacked steamer baskets loaded with potatoes, the top basket took 10 minutes longer than the bottom basket to reach steaming temperature. That makes for extremely uneven cooking.
If you use traditional bamboo steamer baskets as opposed to stainless-steel, you have to let them dry thoroughly after every use or they will mold. That's the price you pay for elegance.
A big benefit of stovetop steaming is that the liquid used for steaming can add flavor to your food and pick up flavor from your food. In a blind taste test, potatoes (which are porous) and green beans (which have a smooth waxy surface) were steamed over plain water, water with rosemary, white wine, and water with sliced ginger. All the flavors were easily detected in both the green beans and the potatoes, although oddly, the ginger flavor was much fainter than the wine or rosemary. Most vegetables won't add a lot of flavor in return to the steaming liquid, because they don't give up much liquid during steaming (this is part of the reason steaming works well with vegetables--they don't dry out). Foods like mushrooms or mussels, on the other hand, give up much more liquid as they cook, and this liquid flavors the steaming liquid. This type of flavor transfer is another big benefit of steaming for some recipes: You can use a small amount of flavorful liquid to cook your food, and in certain cases you can use that cooking liquid to make a sauce, because it picks up the flavor of what was cooked over it.
Commercial steamers If you do want to steam anything more than a small quantity of food, a dedicated steamer is the way to go. Commercial steamers come in a vast array of sizes, from units that reheat single portions to units that can steam a whole cow (if you wanted to).
Most steamers are designed to cook food in standard hotel pans and are rated by how many pans they can hold at one time. When loading food, know that some steamers will bog down if filled to the gills. In addition, steam only cooks well where it can get. If steam can't get to food because of crowding, or steam stagnates and can't move around because you used a solid hotel pan instead of a perforated one, cooking will slow down. You should always load food in perforated hotel pans if possible, choosing the pans with the shortest appropriate height. Food that is messy, such as meat or fish, cooks better in a perforated pan with a drip pan positioned below the cooking pan.
Choosing a steamer can be bewildering. Let's navigate the choices.
Making steam Steamers can use externally generated steam--these are called direct steam units--or can make their own steam internally. Steam for direct steam units can come from a building-operated steam system, another piece of steam equipment in the kitchen, or from a boiler built for this purpose. If you use a central steam supply, it must produce food-grade steam. The advantage of direct steam units is that they cost less than self-contained units. Larger external boilers are also more efficient and economical to run than smaller internal boilers when producing the same amount of steam. But it doesn't make sense to install a full steam system for a single steam cabinet. Plus, if a central system breaks down, you can't use any of the equipment attached to it.
Self-contained units can use a boiler, a steam generator, or be boilerless (also called connection-less). The difference between a boiler and a steam generator: Boilers typically produce superheated steam at elevated pressures, while a steam generator generates steam at atmospheric pressure. Water quality is a big concern with boilers and steam generators. The water used must be clean, potable, and fairly soft. The constant boiling of water in these units causes scale to build up quickly. Regular maintenance is a must, even when using filtered softened water. If you don't de-scale your unit or use water within the manufacturer's specifications, you void your warranty. Boilerless units heat the water for steam directly in the cavity, are easy to clean, and don't have big water quality issues.
Pressure or pressure-less? Although normal steam is always about 212°F, pressurized steam can be considerably hotter, so pressure steamers cook foods more quickly than normal steamers. And they can cook temperature-insensitive foods, like potatoes, extremely quickly. Because pressure cookers are sealed, they are fairly efficient. The disadvantages of pressure steaming stems from the fact that these steamers are sealed: Internal convection is low, which can slow cooking speed and affect evenness. Pressure steamers come in low- and high-pressure varieties. Low-pressure units usually operate at 5 psi (227°F). Low-pressure units can be bigger than high-pressure ones and can be opened and closed fairly quickly. They usually have multiple drawers, each of which holds two hotel pans. Both Cleveland Range and Market Forge Industries make low-pressure steamers in gas, electric, and direct steam models. Cleveland makes two, three, and four compartment units. Market Forge makes two and three compartment units, and also makes an interesting model, the A-Plus steamer, that can operate either as a pressure or pressure-less steamer. High-pressure units operate up to 15 psi (250°F). They usually hold fewer hotel pans than a low-pressure unit of the same size. They also take longer to open because the pressure has to equalize first. On the positive side, they cook food very quickly. Market Forge's Steam-It unit is the most available unit in the United States. Pressure steamers are common in fine-dining restaurants throughout Europe, where Franke is the most well-known brand, but in the United States, they are found mainly in institutional kitchens. Most restaurants in the U.S. use pressure-less steamers.
Traditional pressure-less steaming cabinets Traditional pressure-less steamers use a constant supply of steam to cook food; extra steam that doesn't condense on and heat food is vented out of the cabinet. Because steam is constantly streaming into the cooking cavity of these steamers, the steam is always moving, which means the food cooks quickly and evenly since the constant movement doesn't allow any insulating barrier of cool air to form around the food. Also, because unused steam is vented out of the cavity, the cavities remain relatively dry, so excess moisture doesn't condense on the surface of foods; this is why they can be used to reheat foods like bread. The constant supply of fresh steam also ensures almost zero flavor-transfer between foods.
On the downside, these steamers require a lot of energy and a lot of water. In addition to the water used to create the steam, they require cooling water to recondense unused steam and cool it to below 140°F before allowing it to drain.
Energy ratings The U.S. government established Energy Star ratings for commercial steamers in 2003. To be Energy Star qualified, gas steamers must be at least 38 percent efficient (38 percent of the energy consumed must go into the food, instead of the air and the cabinet), and electric steamers must be at least 50 percent efficient. Using an Energy Star qualified steamer can cut utility bills in half. Unfortunately, most of the Energy Star steamers use electricity rather than gas, and gas is so much cheaper for most Americans that they will continue to use less efficient, older boiler technologies. Fortunately, there are a few gas-fired Energy Star qualified units with steam generators. The Cleveland Range Gemini series and the Market Forge Eco-Tech Plus range of steam generator steamers are Energy Star qualified.
Enter the connection-less steamer Connection-less steamers don't require a drain or a water supply line. Simply fill with water and start steaming. They have minimal venting requirements and have always been the most energy efficient type of steamer available. The large majority of Energy Star qualified steams are connection-less. In the past, the main disadvantage of connection-less steamers was that they couldn't cook as fast as boiler and steam generator units. Over the past decade, connectionless steamer technology has progressed so far that this disadvantage has almost been eliminated. There is almost nothing these steamers can't do. Another disadvantage of connection-less steamers is they can allow flavor transfer between different foods cooked at the same time--say fish and vegetables. Connection-less steam tends to keep vapors–and hence aromas--inside the cooking cabinet. Some manufacturers solve this problem by dividing the cooking cabinet into compartments. Smelly foods and delicate foods can then be cooked separately. On the other hand, connection-less steamers require minimal maintenance. There is no boiler to descale and clean, you don't need to use filtered and demineralized water, and cleaning them is easy.
Unfortunately, most of the very efficient connection-less steamers are electric, not gas. There are only four Energy Star qualified gas-powered connection-less steamers: the AccuTemp Evolution, Cleveland Range's SteamChef 3, Intek's Xtreme Steam, and Stellar Food Equipment's Sirius II. Even these Energy Star units are far less efficient than their electrically powered cousins. Increasing the efficiency of gas-fired connection-less steamers is the next horizon in steamer development.
Every company has its own technology for making fast-cooking, energy efficient steamers. Most focus on circulating the steam within the cavity, insulating the cabinet well, conserving steam when the cabinet is opened, and reducing power during idle time. Here is a rundown of current Energy Star Qualified connection-less steamers:
AccuTemp Evolution: AccuTemp is one of the most innovative steamer manufacturers. The Evolution line is extremely efficient, cooks quickly, and uses very little water. Most companies use fans to circulate steam within the cooking cavity to even out temperature and accelerate cooking. The Evolution steamers accomplish this with no moving parts by passively guiding the flow of steam to every pan. No moving parts, less stuff to break. After cooking, the Evolution can go into a low-power holding mode. AccuTemp steamers also have a unique integrated vacuum pump. As the pump reduces pressure, the boiling point of water goes down. As the boiling point of water is decreased, so is the temperature of the steam. The claimed advantage of low temperature steam is that you can hold more delicate foods hot in a steam environment for long periods of time. AccuTemp makes electric and gas models.
Vulcan C24E03: The C24E03 is a three-pan countertop steamer that packs a wallop. It is compact, simple to use, cooks quickly and efficiently, and uses very little water.
Groen Vortex: Groen's Vortex steamers are designed to operate well with heavily loaded pans. They feature an internal circulating fan, a large water reservoir, and a polished interior that makes cleaning easy. After cooking, the Vortex can be set to go into a low-power hold mode to keep foods hot without overcooking.
Southbend Simple Steam: The name tells you what Southbend is going for: easy use and maintenance coupled with energy efficiency. Units can be serviced from the front for quick repairs if necessary.
Cleveland Range SteamCub and SteamChef 3: Cleveland's Energy Star models have a technology called "Kleanshield" designed to directly condensate out of the cavity to maintain cleanliness and reduce foaming and scum in the water reservoir. Some models also have an auto-fill and auto-drain feature (although that makes them not connection-less).
Intek Xtreme Steam: Billing itself as the best combination of efficiency and cooking speed, Intek uses a proprietary fan system called "inverted flow" to guarantee fast, even steaming. Models are available that run on gas as well as on electricity.
Blodgett SBF-E: The SBF-E is Blodgett's first foray into the boiler-less steamer market. Available in three or five pan size units, the SBF-E creates steam by heating water held in a pan resulting in low water consumption and easy scale removal. A removable steam diffuser plate helps keep large food products from falling into the water pan.
Stellar Sirius II: Stellar makes both gas and electric connection-less steamers. They feature dual fans to ensure even heating throughout the cabinet and fast recovery times when loaded. The walls of the Sirius as well as the reservoir are heated. This reduces condensation in the cavity and directs the energy to the food. The interior of the cooking cabinet is made of anodized cast aluminum, which, Stellar claims, reduces recovery time. The Sirius also comes with an automatic water fill feature and a drain.
Microwave steamers Microwaves are absorbed by steam. If moist foods are microwaved in a covered container, steam is generated. The steam then absorbs those microwaves. At that point the food is being cooked primarily by steaming, not directly by the microwave. The upshot? Microwaves make good steamers.
Panasonic Sonic Steamer: The Sonic Steamer is designed to hold two covered plastic steam table pans (or four half-pans, or six third-pans, etc). It is small, like a microwave. And you just plug it in, like a microwave. It consumes no energy when it isn't being used. Powerful magnetrons generate steam almost instantly inside covered pans. Because the pans are covered, there is no flavor transfer. No water is added; most food can steam with the moisture it already contains. The trick of the sonic steamer is to generate steam very rapidly so foods steam rather than microwave. Because steam is generated inside each pan, heating is even. If you need more capacity, buy more units. This type of technology is best suited to steaming lots of portions on demand, not to steaming six hotel pans of potatoes.
Combi ovens These ovens--from companies such as Alto-Shaam, Hobart, Electrolux, and Rational--make fantastic steamers. The word combi comes from COMBInation steam/convection oven. They can do anything a pressure-less steamer can do--and much more. Sophisticated microprocessors allow chefs to designate complicated cooking profiles with different proportions of steam and dry cooking. These ovens can do anything: roast meats, steam vegetables, bake bread--all in large quantities. They're true marvels. Their main disadvantage is the high cost, both for the purchase and the maintenance.
Indirect steam Not only for direct cooking, steam also can be harnessed to heat cooking vessels. The simplest form of indirect steaming equipment is the double boiler. The advantage of indirect steam is that heat can be evenly and quickly applied with no chance of scorching and burning. Modern indirect steamers include the steam jacketed kettle and the steam griddle. Both of these pieces of equipment have amazing temperature recovery times because of steam's tendency to condense on, and rapidly heat, any cold surface. An indirect steamer's operating pressure determines the maximum temperature it can reach. Unlike direct steamers, the steam in an indirect steamer doesn't have to be food grade: It can contain antifouling agents and other chemicals that increase the life of the boiler.
Steam kettles Steam kettles can either be hooked up to an external source of kitchen or building steam, or contain their own steam boilers. Units with self-contained boilers usually cost more initially but are more efficient because they're sealed systems, meaning the hot condensate returns to the boiler and is reused rather than thrown away. Most kettles with external steam hookups also have to be periodically drained of condensate. This procedure, called blowdown, requires a drain. Other features to look for in a kettle are tilting (makes removing the food a breeze), and a product drain on the bottom (good for stocks or defatting). Like most steam equipment, the venting requirements for steam kettles are low for the amount of cooking they do. Usually, steam kettles won't get above 300°F (at a pressure of 50 psi).
Steam griddles The AccuTemp Corporation makes steamers but is perhaps best known for the Accu-Steam Griddle. It's like a hollow stainless-steel sandwich. Inside the sandwich is high-pressure steam, high enough pressure to get the griddle surface up to 400°F (around 230 psi). Accu-Steam griddles boast instant temperature recovery and no hot spots. As soon as a piece of food hits the Accu-Steam, the thin stainless-steel surface cools down. As the surface cools, steam from the inside condenses on it and heats it back up almost instantly. It operates on the opposite principle from most griddles (big chunks of metal heated for a long time to build up thermal mass).
Getting more information For the U.S. government's current list of Energy Star commercial steamers, see: www.energystar.gov
The best source of information on the efficiency of any piece of kitchen equipment, including steamers, is the Food Service Technology Center in California (www.fishnick.com). Their main steamer paper can be found at: www.fishnick.com It isn't breezy reading, but it's well worthwhile. They also review individual pieces of equipment for cooking capacity and efficiency (www.fishnick.com).
Another great resource is the National Association of Food Equipment Manufacturer's Handbook of Steam, found at: www.nafem.org.