Featured, Food Manufacturing

How a spud becomes a snack – The steps involved in frying raw potato

Potato chips are consistently a top seller in the highly competitive snack food market. To maintain competitiveness, manufacturers have developed a wide variety of flavours and styles. The production process however is fairly similar between them, and processors generally seek common objectives such as a finished product with no defects, crumbs, or blisters, with a good appearance and a bright color.

Making potato chips begins with the raw potato and ends with the final packaged product. This article covers the middle part of the process — frying the washed, peeled, and sliced product — before it goes to inspection and packaging.

Image: Heat and Control Pty Ltd

Frying In Oil

Frying time and temperature varies depending on the variety of potato, specific gravity, slice thickness, and possible sugar content reduction. These two parameters of frying are not constant and must be adjusted to produce uniform quality chips. Generally, a higher temperature translates to a shorter frying time and less oil absorption. An excessively high temperature will result in burnt or caramelised chips and quicker oil breakdown.

The steam released from the potatoes forms a blanket of non-oxidising gas over the oil. This furnishes the steam blanket as well as providing a continuous deodorisation of the oil. A positive effect is that undesirable products do not accumulate because of a rapid turnover of oil, a result of constant replenishment with fresh oil to compensate for what is absorbed by the chips. A negative effect of water vaporisation is that antioxidants, such as butylated hydroxytoluene (BHT) are steam distilled out of the oil. BHT delays rancidity and flavour deterioration in the potato chips.

Specially designed equipment can be provided to increase the temperature of the chips after they emerge from the fryer and this provides a significant reduction in oil content. As steam is being rapidly released from the slices, oil absorption will be low. As the protective layer of water vapor begins to disperse in the final stages of frying, fat enters the voids left in the dehydrated cells.

Factors Leading to Oil Deterioration

Hydrolysis

This occurs when chemical bonds holding triglycerides together are broken by water, creating free acids. Frying systems with high oil turnover rates usually maintain acceptable oil quality and the steam released tends to strip free fatty acids (FFA) from the oil.

Oxidation

The primary reaction is the formation of hydro peroxides. Higher numbers of double bonds in the unsaturated oil will increase the rate of oxidation. This reaction is enhanced by heavy ions. Copper is a potent oxidation catalyst, and its use must be avoided. No copper fittings or brazings should be used in frying equipment.

Polymerisation

The two major types that occur are:

Oxidative polymerisation — free radicals are formed when hydro peroxides decompose at high temperatures and combine, doubling the weight of the triglyceride. Eventually, as the molecular weight increases, they are no longer soluble in oil and will be deposited on the fryer wall.

Thermal polymerisation — primarily occurs at hot spots on the frying equipment, caused by localised overheating.

The oil used for frying has two functions:

  • It serves as a medium for transferring heat from a thermal source to the potato slices.
  • It becomes an ingredient of the finished product.
  • Some factors affecting the amount of oil absorbed by the potato slice include:
  • Solids content of the potato
  • Oil temperature
  • Duration of frying time
  • Thickness of slices
  • Variety of potato
  • Condition of potato
  • Slicer operation
  • Conditioning
  • Type of slice (wavy or flat)
  • Relationship of FFA to smoke point of frying oils

FFA’s increase during frying, due to a reaction between the oil and the water released by frying. FFA will rise and should be maintained below 0.5%. This reaction causes the oxygen to react with the double bonds in unsaturated FFA. Any values above 0.5% will detrimentally affect the quality and shelf life of processed food.

Initially peroxides are formed, which in turn breakdown to ketones and aldehydes. The peroxide value may be helpful in measuring the degree of oxidative rancidity in the oil.

The ‘smoke point’ is the temperature indicated when the oil gives off a thin, continuous stream of bluish smoke. The smoke point of the oil is an excellent indicator of fresh oil quality. Good oils (as received) will have a smoke point of well over 250°C as the oil is used the smoke point will be proportionally reduced.

Versatile Vacuum Frying

Processors of potato chips can increase their processing capabilities substantially with vacuum fryer technology. Heat and Control’s Unitized Vacuum Fryer (UVF) is a self-contained vacuum fryer that saves space and controls acrylamide.

This complete system is designed and manufactured by Heat and Control to process 500 kg per hour of finished potato chips and features support/auxiliary equipment made up of a Vacuum Generation System, KleenSweep®, Centrifugal Oil Filtration System, Heat Exchanger, Fryer Support Module, PLC System Controls, Automatic Heated Centrifuge, and Fryer Support Platform.

The patented UVF is unique because it does not have an external vacuum chamber. It’s Unitized design eliminates an external vacuum chamber — the fryer is its own vacuum chamber, similar to a ship-in-a-bottle. This makes it significantly easier to maintain and to clean, requires less floor space, and allows the vacuum fryer to act like a regular non-vacuum fryer.

This innovative UVF technology from Heat and Control offers snack processors a chance to diversify their product offerings. Unlike traditional frying systems, it enables the conversion of high-sugar food items into snacks, unlocking fresh avenues for innovative snack development. The UVF can fry high-sugar content products like apples, carrots, sweet potatoes, high-sugar potatoes, and beets without causing excessive browning. Furthermore, it effectively reduces the formation of acrylamide by frying at lower temperatures.

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