To ensure businesses are run successfully, food processors need to select carefully the appropriate frying system and also consider the oil which is best suited to their technology and product, while at the same time maintain a good oil management to ensure high oil quality.
There are 3 main reasons that cause a cooking oil breakdown and they are oxidation, hydrolysis and polymerization. Oxidation happens when air comes into contact with oil while hydrolysis is caused by water interacting with oil causing end-products to have an off-flavor. Hydrolysis could be caused by the increasing number of heating and cooling cycles of the oil, metal alloys and emulsifiers amongst others.
Meanwhile, oil which deteriorates form both volatile (or reactive) and non-volatile compounds. Non-volatile compounds remain within the frying oil and can produce polymerization. These molecules bond together to form large, different-sized clusters that accumulate on the oil surface and areas of the fryer. Since they do not dissolve, they cause foaming (e.g., trapping air in the oil), increase the possibility of hydrolysis, and make the fryer difficult to clean.
Choosing the right cooking oil
Selection on cooking oil depends largely on market consideration. The end flavor could dictate what type of oil to use. Consumer preference might force processors to minimize the level of saturated fats in the final product. Increasing the level of unsaturated oils would result in greater oil instability—an important consideration when selecting frying machinery.
Environmental requirements are also crucial. Some oils solidify under ambient conditions, so effective oil-handling techniques associated with correct oil storage and transfer equipment need to be considered.
Processors must ensure that their oil is suited to their cooking technique. For example, confectionery manufacturers can only use certain oils to fry nuts, so as not to contaminate their chocolate. If oil turnover within the fryer is long — as is the case in nut frying — a more stable oil may be required. Additionally, processors must check that oil standards are met. It is essential that they establish what they perceive to be a minimum level of oil quality and ensure that the supplied oil complies within this standard.
The quality of refined oil can be compromised at any level—from raw feedstock, through the refining stage, leading up to and including the distribution of the refined product. Low-cost oil may not be the best solution. Furthermore, some oils may need to have a chelating agent (to prevent particle build-up) added to fresh oil before it is poured into the fryer, in addition to antioxidants or anti-foam additives.
Establish oil quality standards, whether it is FFAs (free fatty acids), TPM/TPCs (total polar molecules/total polar compounds), or PVs (peroxide values), and stick to those standards. If you surpass your limit thresholds, the oil will continue to degrade, resulting in reduced to unacceptable product quality.
Proper storage and handling
During delivery, bulk oil should only be received via vehicles designed for oil handling. In addition, the vehicle should be clean both on the outside and on the inside to prevent contamination. During transfer, care should also be taken so that the oil is not accidentally aerated. This is especially important when the tanker is almost empty.
Oil-storage tanks should be sealable to slow the flow of air into the headspace. Ideally, they should be injected with some form of inert gas, like nitrogen. In addition, tanks and pipe work should be constructed of materials that will not compromise the oil – copper or brass parts are not acceptable. In terms of maintenance, tanks and associated pipe work may need to be traced or heated to maintain oil in a liquid state. Cleaning should be done routinely to keep the storage tank hygienic.
Smart equipment selection
There are a variety of different fryer styles and configurations available to processors depending on their requirements, ranging from large, continuous systems to small, restaurant-style batch units.
Consider the following factors when selecting a fryer system:
- What are the desired characteristics of the finished product?
- How many kg per hour of final product are required?
- How much heat energy is required and what type of heater is needed?
- What level of oil filtration is required?
- How much oil will be absorbed or given off by the product during cooking?
- How will the machine affect oil selection?
- What is the size of the raw/cooked product ? Does the product have any special frying characteristic, such as sink, float, sink then float? This will determine the type of conveyance mechanism required to bring the product through the fryer.
- Does the end product have any special characteristics?
- How easy is it to clean the fryer ?
Well-designed fryer systems address processor needs and help to maintain oil integrity within the fryer.
The following are factors to consider when preventing oil degradation:
The fryer should be sized to suit the heat load, production capacity, and output requirements. If systems are sized too large for production capacity, then the oil turnover time can be too long, causing oil to breakdown too quickly before it can be replaced by fresh make-up oil. If the heater is sized too small, the output may have to be reduced, again causing oil quality to suffer.
Maintaining the correct oil level will minimize oil and product quality issues.
This ensures that the frying oil is exposed minimally to air. This is done by various methods (e.g., steam blanketing, internal baffles, controlled air flows). Each technique is designed to prevent oxidation, the process where air interacts with the hot oil.
Materials should be manufactured from functional materials that do not compromise oil quality. Most modern equipment is manufactured from stainless steel; however, carbon steel is acceptable in certain instances. Brass or copper should never be used because it reacts chemically with cooking oil, immediately making it rancid.
Filtration removes particulate material or debris, commonly known as fines, before it compromises the end-product or degrades the oil. Fines left in the fryer will burn and carbonize, and burnt fines are one of the greatest contributors to degrading oil quality. Using an absorbent that removes FFAs can rejuvenate the oil.
Effective Oil Heating
Oil heating systems should be designed both to fulfill heat-load requirements and to minimize any oil damage from excessive heater/oil-film temperatures.
Low Oil Volumes
Minimized oil volumes within the fryer system reduce the time needed to replace old oil with fresh make-up cooking oil as oil is absorbed into the product and taken from the system. This, in turn, helps control oil condition.
Ease of Cleaning
The system should offer features that help cleaning procedures. It is important fryer systems have built-in clean-in-place systems for efficient, automated cleaning.
The removal of water from a fryer system after cleaning is crucial, not only for maintaining oil integrity but also for user safety.
To maintain good oil quality, a food processor can start heating as late as possible when production is about to begin. Keep the fryer hood closed to maintain the modified atmosphere. Oil can also be conditioned by adding older oil to fresh oil to maintain the desired flavor characteristics. Upon shutdown of production, oil should be cooled to below 250°F/120°C as quickly as possible and then stored in an appropriate storage area. Finally, the frying system should also be cleaned regularly to minimize oil deterioration apart from complying with HACCP standards.
Contact your local Heat and Control representative for professional advise, information and support on the right frying equipment as well as on the right frying processes. Heat and Control offers a network of engineers, food technicians and support teams at its 10 manufacturing facilities, 11 test centres and more than 30 offices globally.
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