Deep-frying is becoming more and more popular as the food manufacturing industry offers quality products which can be deep-fried and frozen such as french fries, shrimps, spring rolls, meat products coated with breadcrumbs and some vegetarian products.
As well as having a long shelf life, these frozen products are quickly and hygienically prepared to suit a variety of menus.
During deep-frying, the water contained in the product is used for cooking.
The water is vaporised by the high temperature (typically 170°C to 175°C) of the oil but is simultaneously bonded by the oil so that it cannot immediately escape to the ambient air.
In this way, a type of ‘vapour baking’ takes place. However, the cooking oil used must be sufficiently fresh, otherwise the food will soak up the oil.
The deep-fried food would then have an unwanted dark brown colouration and substances could be released which are difficult to digest or which are thought to cause cancer.
Rapeseed oil, peanut oil or coconut oil, either pure or in mixtures are often used as cooking oils.
Oil ageing
Ageing at room temperature can lead to rancidness, caused by an oxidation reaction between the air and the oil.
As well as this, the quality of the oil is influenced by the effect of heat and by the food that is deep-fried in it.
This is referred to as thermal oxidative modification of the cooking oil.
Scientific research has shown that the so-called polar components or total polar materials (TPM) are a good indicator of the thermal oxidative load of cooking oil.
They are also an indication of how used the cooking oil is.
A high level of polar components indicates that the cooking oil has been used frequently.
Measuring methods
The polar components are measured using column chromatography.
In many countries, it is the reference method used by federal research institutes and food laboratories.
The different components of cooking oil are separated in a column (a pipe-shaped glass body) according to the retention principle.
However, the measurement of polar components according to this method is usually limited to laboratories with trained personnel on account of the complexity involved and the experimental set-up necessary.
This method is unsuitable for use in industrial kitchens. However, polar components can also be measured using a physical parameter: the dielectric constant.
Increasing polar components in cooking oil has the effect of changing the dielectric constant because the polar components are aligned in an electrical alternating field.
The change in the dielectric constant is measured on a capacitive basis using a special sensor and is converted to the required percentage TPM display variable.
In this way, fast electronic measurement of this reading is possible.
Solution
Testo has developed a compact, electronic hand-held instrument for daily use.
The main part of the instrument is a sensor developed by Testo, which can be immersed directly in the hot cooking oil.
After approximately 25 to 30 seconds, the instrument shows the number of polar components directly in the display.
The current cooking oil temperature is shown in a second display line.
Two limits, which trigger a light emitting diode displaying different colours dependant on the oil quality, can be set in the instrument making operation easy for all staff.
If this light emitting diode is green, the cooking oil is fresh; a yellow display indicates that the oil is slightly used; a red display indicates that the oil should be changed soon.
Both limit values (threshold values from green to yellow or yellow to red) can be defined by the user. In this way, anyone can measure cooking oil quality quickly and efficiently.
Hygiene
The instrument does not need to be adapted to the cooking oil used, so is suitable for any standard oils and fats.
The tester is easy to clean under running water if it comes into contact with cooking oil as a result of the ‘TopSafe’ protective case supplied.
Since the ‘TopSafe’ is resistant to heat, it can be cleaned in the dishwasher to ensure it remains hygienic.
The Testo 265 can measure cooking oils ranging from 40°C to 200°C via its built-in temperature compensation function. If this value is exceeded, it is shown clearly in the display.
The temperature display will mean it is no longer necessary to have additional thermostat checks on the deep-frying bath, using a separate electronic thermometer.
www.testo.com.au