FOLLOW THE PROCESS
Frying oil has a strong impact on the shelf life of the snack.
The frying temperature for pellets depends on their characteristics but typically, it ranges between 180 and 200°C, while in case of natural potato crisps it ranges between 160 and 180°C. Because of the high processing temperature, it is necessary to use oils with high thermal stability.
Triglycerides are made of saturated, mono-unsaturated, and poly-unsaturated fatty acids. Oils rich of saturated fatty acids are heat resistant, but give a fatty off-taste to the product and they are not recommended by the recent nutritional guidelines. Oils rich of mono-unsaturated fatty acids have a good thermal stability and they resist well to the frying process up to 195 ÷ 200°C. They have a neutral taste , and there are no concerns from nutritional point of view. They are less cheap and they are less used. Oils rich of poly-unsaturated fatty acids, do not have a good thermal stability (smoke point 150 ÷ 160°C only), they tend to form peroxides reducing the shelf life of the product. Moreover, they tend to cause gumming in the fryer and on the conveyors.
As a general indication, a GOOD OIL for frying pellets should maintain during the process the following values:
- Free Fatty Acids: FFA 0.3 – 0.4%
- Peroxide Index Value: PIV < 7 – 8
Higher levels thereof are an index of a degraded oil which may lead to a shorter shelf life of the finished packed snack.
Main TYPES OF OILS:
Standard Sunflower Oil
It is known to cause gumming in fryers, due to the formation of high molecular weight polymers and as consequence it leads to an increase in oil viscosity. It needs regular cleaning, to avoid oil deterioration. Its stability is not sufficient for frying temperatures higher than 180°;
High-Oleic Sunflower Oil
It is a good quality oil of about 80% of oleic acid (mono-unsaturated) with a good thermal stability, a good oxidation resistance, and a neutral taste. Melting point is 0,5°C;
Fractionated Palm Oil (Palmolein)
Chemically and physically it appears to be particularly stable and clean for frying, as well as relatively cheap. Since it contains natural anti-oxidants, further chemical additions are not required. It is probably the most used worldwide for frying pellets, although it is object of recent concerns from nutritional point of view cause of its content of 30-40% of palmitic acid (saturated acid);
Maize or Corn Oil
It is not widely used for commercial frying and its problems are commonly related to a low thermal stability and consequent gumming in the fryer, and its relatively short life;
They are generally unsuitable for frying pellets, but in the past they were used after hydrogenation process. Nowadays, trans-fatty acids formed during the hydrogenation of oils are a major concern from health point of view.
Pure Soya and Rape seed Oil
Other aspects which are essential for achieving an adequate shelf life of the fried product:
- suitable design of the fryer (heat exchanger characteristics, oil filtering system,…);
- handling of the fryer to ensure a short oil turnover time (running fryer at maximum output capacity,…);
- good cleaning practices to reduce to the minimum the formation of products with high molecular- weight;
- using of anti-oxidants in the frying oil (natural or synthetic);
- nitrogen injection into the snack’s bag;
- characteristics of the packaging (bag film).