Low Temperature:Cook and Hold Ovens

Dan Bendall

Technological advances, coupled with rising labor and food costs and the desire for better roasted meat products, led to the development of low-temperature, cook-and-hold ovens.

Since the beginning of recorded history, man has been cooking food. Initially, this was cooking done on a spit over an open fire. In the Middle Ages, enclosed stone and brick-lined ovens were used. Later, various ways of regulating heat were introduced and other fuel sources besides wood, such as natural gas, were implemented. These fuel sources, along with indirect heating, allowed temperature control over the cooking process. Chefs discovered that varying cooking temperatures would change some characteristics of foods.

Slow or low temperature cooking is not a new invention. It is possible that early man first used this method for producing juicier meat and reducing shrinkage. Low temperature cooking was practiced in Colonial America, but did not gain a substantial following in commercial cooking until the last two decades or so. The introduction of convection ovens in the early 1960s and the availability of more precise thermostats for controlling temperature were the first major developments in oven technology in many years. The technology, coupled with rising labor and food costs and the desire for better roasted meat products, led to the development of low temperature ovens. In recent years, cook and hold oven manufacturers have recognized the food quality desired in today’s marketplace. They have responded and added many features like precise temperature control, programmable menus, and variable humidity control to effectively provide low skilled workers the tools to deliver superior finished products.

What is a low temperature oven?
A low temperature oven is specially designed to hold precise temperatures and keep the entire oven cavity at a uniform temperature. The uniform temperature can be maintained by either introducing air movement into the oven or by heating the entire inner surface of the cavity. Cooking temperatures vary by type of product being prepared, but typical roasting temperatures for meats are 200°F to 225°F. Most ovens that are designed specifically for low temperature roasting are electrically heated, but there are some natural gas-fired models, most of which can also be used for high-temperature baking and other oven applications.

The cook and hold oven, or retherm oven as its close twin is called in schools and hospitals, has been found to be an excellent way to prepare many convenience foods. Frozen prepared dishes with sauces or gravy, such as ravioli, chicken cacciatore, or macaroni and cheese, are specially well-suited to cook and hold methods. When these institutional foods packed in aluminum trays are cooked at high temperatures, much of the moisture evaporates and sauces tend to crust and burn at the edges. Low temperature cooking slowly thermalizes and heats the product through while preserving its desired consistency.

Purchasing factors to consider:
Look carefully at what is available in the market place for oven features that are desirable for your operation. There are a variety of sizes of ovens available. Some small ovens hold one to six roasts with work tops or carving station tops. These can be used on a buffet line or as an equipment stand in a kitchen of limited space. Consider a larger unit if your expected demand warrants it. Recognize that most of these ovens are not cheap and many are more expensive than similar sized conventional ovens. Accessories should also be considered.

Casters for the oven are necessary if you anticipate moving it between areas of preparation and serving. Some units are available with smoker attachments for preparing smoked meats. However, beware of taste transfer from a smoker when not preparing smoked products. The smoker will have to be cleaned very thoroughly or another oven will need to be used for most non-smoked products. Look for a unit with digital temperature and time display and an automatic doneness probe, if these items are important to the operation.

Some oven manufacturers have chefs on staff who are knowledgeable about foods and how they can best be prepared using the cook-and-hold concept. Use these chefs as resources and then talk to other users of the ovens. You may find that low temperature cooking will provide the quality of product wanted with lower food costs.

The convection-type ovens employ a heating element, usually at the top or bottom of the oven, with a fan that circulates air through the cavity and around pans of product which may be cooking.

The “hot wall” oven, another popular cook-and-hold way of heating, uses the conduction method of heat transfer to surround foods with heat over a long period of time. Some ovens of this type use a heated metal wire element embedded in the inner wall of the oven. The elements are wrapped tightly in order to give a consistent temperature throughout the cavity without cold spots. Other types of hot-wall ovens channel hot air around an interior cooking compartment. The inner compartment is completely suspended inside an exterior wall with heated air between the two.

Another distinctive variation is low-temperature conductive cooking technology, which is accomplished by circulating a fluid through heat transfer plates in each oven shelf. The heat is then transferred directly into the cooking pans or containers from the shelf rather than by circulating hot air to cook. Manufacturers of each of these non-convection ovens claim greater product yield over convection styles as a result of less drying and more moisture retention in product.

Convection ovens designed for slow cooking are typically made with a fan that gently moves air through the cavity to produce even heat. The air is forced through the oven at a lower velocity than in a high-temperature convection oven. High-temperature convection ovens with slow roasting capability sometimes have a two-speed fan with the low speed being most desirable for low temperature cooking. The holding mode may or may not use the fan.

The cook-and-hold principle, while not exclusively related to low-temperature cooking, often naturally complements that cooking process. A cook-and-hold oven first cooks or roasts at a certain temperature for a set amount of time to produce desired doneness in the product. Once that set time expires, the oven automatically switches to a holding mode that stops cooking the food and holds the temperature above the danger zone for bacterial growth. This present holding temperature is usually 140°F to 160°F. The holding temperature will be maintained in the oven until the oven is turned off or the timer is re-set.

New technology in cook-and-hold ovens incorporates integrally wired meat probes that automatically regulate the cooking time of a product. The solid state controls are set for the oven to switch over to the holding mode once the desired internal temperature of the product is reached. These meat probes allow for a more consistently cooked product and take the guesswork out of timing various sized cooking batches. When using a timer, the operator must take into account the size of the individual product being cooked, as well as the number of pans or roasts cooked simultaneously. The meat probe feature is expected to become increasingly popular in the future as operators become more comfortable with the technology.

A further development is fully programmable controls that program the unit for a week’s activity. For example, the oven can be programmed to preheat a half-hour before cooks arrive in the morning so time and energy is not wasted.

Why use cook and hold?
There are numerous advantages to using low temperature cooking, with only a few drawbacks. The primary advantage is the reduced shrinkage of roasts during cooking. To an operator, reduced shrinkage means more salable product. As much as an additional portion or more of prime rib for each rib roast could be saved. Manufacturer’s claims for shrinkage percentages vary widely, as do studies carried by schools and independent organizations. The true shrinkage ratios that a particular operator experiences depend on the cut of meat, trim, grade, moisture content, degree of cooking doneness, and packing and handling of the product before cooking. With the number of variables involved, it is understandable why different tests produce such different results. Rib roasts cooked at 200°F to 225°F typically yield 10 to 15 percent shrinkage. The same roasts cooked at 350°F or higher shrink approximately 25 to 35 percent or more. Remember that many types of meat are over 60 percent water and contain a large amount of fat. With these proportions, it is easy to see how shrinkage is an important factor to consider in meat cooking.

Other advantages to slow roasting are that lower temperatures generally require less gas or electrical energy. Even though the cooking times are longer, the temperatures are lower and require less fuel. In areas where a restaurant is charged an electric demand fee, overnight cooking may be an even greater expense advantage since electric demand is usually low when the restaurant is not in operation. Labor savings can also be achieved by overnight cooking. If the product is started in a lower temperature oven, it can be left unattended for many hours while it automatically cooks and holds. When using higher temperature cooking with shorter times, staff may have to come in before the serving time to cook that day’s product, thereby extending work hours.

The holding cycle (140° for roast products) will aid in the tenderization of meats and enhance their taste. The tenderization is the product of natural enzyme activity that occurs in meats when held near 140°F. These enzymes break down some of the tough muscle fibers in meats. Lower cost cuts of meat may be used and become more tender when held for several hours.

Here’s another advantage: low temperature ovens are usually not required to be located beneath exhaust hoods. In a large facility having several low-temperature ovens, the cost of a ventilator can be sizable, not to mention the increased load on the heating and air conditioning system.

The disadvantages to cooking at low temperatures are that the process takes longer and it requires additional forecasting of product needs by the kitchen staff. Many chefs feel it is a disadvantage to not have the crisp, caramelized outside on meat products that they are used to having with high-temperature roasting. If cooking is done at above 212°F, however, some carmelization will occur in low temperature ovens.

Most of what has been mentioned here about cooking has referred to roast meat products. Many other foods can be prepared in a low temperature cook-and-hold oven. Other meat products, such as poultry, ham, and pork can be cooked with similar advantages to those mentioned above. In general, however, baked bread products do not turn out as well when cooked at low temperatures, and most of the advantages relating to shrinkage and holding are negated.