Potato Product Fryers 101:
Selecting the right fryer design
As PotatoPro, we believe that selecting the right fryer design is one of the most critical decisions in potato processing. We also find that its importance is often underestimated.
That's why we are pleased to offer you this article by Don Giles, Director of Sales, Processing Systems at Heat and Control. In this article he provides an overview of the different fryer types available and explains how specialised fryer designs can improve productivity and quality.
Batch fryers are used exclusively for hard bite, slow cooked potato chips due to their unique temperature profile.
The high-moisture content of potatoes requires a specially designed batch fryer. Potato-specific batch fryers use a kettle of static, hot oil – direct-heated by a gas burner firing under the fryer pan or by heat-transfer tubes immersed in the oil. These tubes can be heated by a gas burner, steam, or thermal fluid.
As each batch of potato slices enters the oil, the cooking oil temperature drops and then gradually increases as the burner fires to regain the proper frying temperature. This “inverted bell curve” temperature profile produces the distinctive hard-bite texture that has made these chips the fastest-growing segment of the potato chip market.
The art of adjusting this oil temperature profile gives processors the ability to create subtle differences in chip texture. Once these cooking parameters are set, sophisticated batch fryers use a Programmable Logic Controller (PLC) to assure repeatable frying of each batch of chips. Batch fryer capacities range from 35 to over 500 pounds, (15 to 225 kilograms) of finished potato chips per hour.
Advantages of Batch Fryers
- Low cost (compared to continuous fryer systems)
- Adjustable temperature curve produces chips with unique textures
- Slice stirring systems unload the finished chips and enable one operator to handle multiple batch fryers
- Minimal floor space
- Versatility: cooks other types of root crops in addition to potatoes
Limitations of Batch Fryers
- Production capacity is limited by the fryer’s surface area and heat input capability
- Automatic stirring systems eliminate the hazardous, labour-intensive task of manual stirring
- Product must be stirred for uniform cooking and to prevent slices from sticking together in clusters
- Large oil volume with relatively slow oil turnover rate
- Some older models provide only partial removal of fines, leading to degrading oil quality and leaving black specks on the chips
There are numerous designs of continuous fryers, varying in heat load, product handling, oil filtration, and production-capacity, however all commonly cook a continuous flow of product.
Potato products such as potato chips, sticks, potato co-products such as tots and patties, french fries, or batter-coated fries require an externally-heated continuous fryer design due to the large amount of moisture that must be boiled off during the frying process, as well as factors such as:
- Responsive, accurate, and consistent temperature control
- Higher thermal efficiency than direct-heating
- Heat load is not limited by size of fryer due to the fryer and heat exchanger being sized separately
- Higher capacity production
- Lower system oil volume (including fryer, heat exchanger, fiter, and piping) than direct-heated fryers
- Continuous removal of product particles
- Rapid oil turnover rate
- Oil flow is adjustable to match product flow rates
- Minimal cleaning required as fine particles remain suspended in the circulating oil for more efficient removal
Continuous fryers are available for 200 to 6,500lbs (90 to 2,900kg) of finished potato chips per hour and over 50,000lbs (22,000kg) of par-fried french fries per hour.
Continuous oil circulation provides multiple advantages:
- Maintaining a consistent oil temperature and temperature drop through the fryer
- Separating and advancing products through the fryer for uniform cooking without clusters
- Keeping product particles in suspension for more-efficient filtration and clean fryer operation
Unique characteristics and production capacities of different potato products have prompted the development of specially-designed continuous fryer systems, including Multi-Zone Fryers, Multi-Stage Fryers, Thermal-Fluid-Heated Fryers, and Vacuum Fryers.
This enables processors to develop custom colour and texture characteristics for different products. It also permits frying at lower temperatures, which produces lighter colour product and reduces oil degradation.
(Click to enlarge)Multi-Stage Fryers are a variation of the multi-zone design and provide a greater range of frying temperatures.
Two Stage Heat and Control Fryer for coated French Fries (More on this fryer)
Each fryer stage uses a separate continuous oil filter, oil-circulation pump, and heat exchanger.
Multi-stage fryer systems are especially useful for batter-coated fries, french fries, or fine particle-intensive co-products.
Thermal-Fluid-Heated Batch FryersThis direct-heated fryer uses a patent-pending thermal-fluid heat exchanger that heats oil uniformly throughout the fryer.
A fines removal conveyor and spacing between the heat transfer tubes prevent product particles from accumulating inside the fryer.
(Click to enlarge)Operating at 10 percent or less of normal atmospheric pressure, a vacuum fryer boils off product moisture at a lower temperature than traditional fryers.
Heat and Control unitized Vacuum Fryer (More on this vacuum fryer)
This means high-sugar content potatoes can be fried without browning of finished chips. Formation of acrylamide can be controlled because oil temperature can be kept below the 248°F /120°C point at which acrylamide forms.
Heat and Control's advanced vacuum fryer design requires no external-vacuum enclosure and takes about the same floor space as a traditional, externally-heated, continuous fryer.