Cooking: Back to basics

Poultry industry markets have evolved drastically over the past 40 years. Further processing represents the majority of the products produced today, and commercially cooked products are very popular products in that market segment. Ready-to-eat products in the marketplace offer consumers convenience, quality and value.

Poultry meat is cooked for preservation as well as for sensory qualities. Cooking is a method of pasteurization in order to kill pathogenic bacteria such as salmonella. Products are required to be cooked to a minimum internal endpoint temperature of 71 C for commercial cooking. However, processors often cook to higher temperatures to ensure that all products are cooked to the minimum endpoint temperature, allowing for product or process variations.

The drawback to cooking to higher temperatures is that this results in higher yield loss and quality deterioration. Therefore, it is important for processors to assess their data from temperature checks so that the variation is minimized and the average endpoint temperature is not drastically above the required endpoint temperature. Minimizing this variation will generally require adjustments to be made to the raw product (i.e., uniformity) and/or cooking process.

Sensory qualities and yield

Sensory properties, or eating quality, of meat are important to consumers and sensory quality can be impacted by cooking. Processors are concerned with not only sensory quality, but also with yield as it can also be impacted a great deal by cooking. Meat is transformed from a raw state to a cooked state during the heat transfer process of cooking, and this transformation results in sensory changes. The meat proteins undergo heat denaturation in the cooking cycle, which results in changes in texture, appearance, aroma and flavor.

The heat causes the proteins to unwind and then wind back in a tighter configuration. This tighter structure results in shrinkage of the myofibrils, or muscle, and a more firm structure/texture compared to the raw state. This process also causes a loss of water-holding capacity as the water is expelled into extracellular spaces, resulting in a loss of juiciness and yield. The color also changes from a pinkish color to an off-white/light beige-brown (depending on light or dark meat) in color, and the flavor generally changes to “meaty, roasted.”

Furthermore, depending on cooking conditions, products will undergo the Maillard reaction, or non-enzymatic browning. The Maillard reaction is a chemical reaction that occurs when amino acids (proteins) and reducing sugars react in the presence of heat. The results are a golden brown color as well as some flavor and aroma attributes. Browning is a positive characteristic, especially for appearance of the product, and cooking parameters can affect this reaction.

Temperature gradients

Cooking is the process of heat transfer. Heat can be defined as energy that is transferred as a result of a temperature gradient. The rate of heat transfer is determined by the temperature gradient between the cooking medium and the product and more specifically, between the product surface and core. The rate will generally be higher when there is a larger gradient, and when the product nears the internal endpoint temperature, the rate slows because the gradient is smaller.

Heat transfer can be achieved through conduction, convection and radiation. Conduction heat transfer is where surface particles touch, or the product comes in contact with the cooking medium. Frying, steaming, and grilling (direct contact) are examples of conduction type of cooking.

Convection heat transfer is where free or forced air/liquid is used to gain heat transfer. Steaming and baking are good examples of convection cooking.

Radiation uses wave transmission of energy and the use of the infrared (use of heated tiles) and microwave are examples of this heat transfer method. All of these types of heat transfer are used alone or in combination in various cooking operations in order to maximize yield and quality.

Product characteristics

Some of the product characteristics that are important in cooking are the core temperature, surface browning, juiciness and yield. These can be affected by cooking parameters.

Increasing the temperature, dewpoint (temperature at which vapor first condenses), air speed, and cooking time will all increase the core temperature of the product; however, all of these parameters with the exception of increasing dewpoint, will also lead to decreased juiciness and yield. Therefore, processors must find a balance so that all the positive attributes are realized. For example, cooking in high humidity (before the dewpoint) will lead to increased cooking rate (temperature increase), yield and juiciness.

If browning is also important to the end product, it should not be cooked in high humidity the entire time because the product is incapable of browning in the high-humidity environment. Once the product surface temperature has passed the dewpoint, the surface will dry and browning can occur.

Many commercial ovens available are capable of cooking in both high-humidity and low-humidity environments so that positive product attributes can be maximized. For example, when cooking chicken breast fillets, the fillets would first be cooked in a high-humidity environment. In this section or zone, the product’s core temperature can increase at a fast rate, but because of the high humidity, moisture loss from the product can be minimized. At the dewpoint, the product will continue cooking usually through convection/impingement means and as a result, the surface will begin to dry and browning will begin.

In the end, a balance between safety, yield, eating quality (juiciness), and appearance (browning) can be achieved.

Frying methods

Frying is a popular method of cooking, and there are many battered and breaded products available in foodservice and in retail. Frying uses conduction and convection heat transfer methods and is therefore an efficient method of cooking.

Typically, coated products are fried. This causes moisture to be lost from the product and it also allows the product to absorb oil. Frying is an important step in producing coated products.

Products can either be partially fried (par-fried) or fully cooked. Regardless, the initial frying period sets the coating (adhesion) and starts color and flavor development. Frying (par-fry or fully cooked) also imparts a “fried” flavor which is appealing to consumers. By only par-frying products, more moisture can be retained resulting in higher yields. When fully cooking products through frying, more moisture is driven off resulting in lower yields. However, oil is absorbed in the frying process so some yield is gained.

When frying, it is important to properly manage the oil for best quality and highest yield. Type of oil when frying also affects yield, nutrient composition of the food, and sensory characteristics in addition to shelf-life of the oil. Fresh oil must be continually added and the oil needs to be filtered.

Ovens: Yield, speed and sensory factors

Ovens are also popular in cooking operations for many products and they can operate using several types of heat transfer mechanisms. Ovens can be linear or spiral and they can use horizontal or vertical air flow. They provide heat transfer through conduction and convection.

Spiral ovens are generally used for products requiring more cook time and when floor space is an issue.

Ovens can be used for steaming by injecting external steam into an oven. Steaming can cook products rapidly yet reduce yield loss, but steaming is incapable of browning. Therefore, other heat transfer methods are used when browning is necessary.

Impingement ovens have high speed vertical air flows and they provide a fast cook time, good browning, but it can lower yield because of the dry environment. With an impingement system, there is a forced layer of heated air that penetrates the product thereby aiding in faster cook times.

Convection ovens generally have low air speeds, either horizontal or vertical, and result in a slower cook times. Combining steaming, impingement, and convection systems can offer the processor higher yields, fast cooks, as well as good browning.

Ovens are also often used in combination with frying operations. Coated products are often fully cooked using ovens, after a par-fry period in the fryer, using the steam sections for rapid increase in product temperature and convection sections to finish the cooking process, allow browning, and to get a crispy texture. Again, the par-fry period is important for coating properties such as adhesion, color and flavor. However, the use of the oven for fully cooking products instead of a fryer can reduce moisture yield loss.

Cooking operations have evolved a great deal over the past 40 years. The right combination of cooking methods can maximize safety, yield and quality attributes so that both the processor and consumer win.