FNB News - Cold storage key for edible oils, as temp affects shelf life

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F&B SPECIALS

Cold storage key for edible oils, as temp affects shelf life

Sunday, 01 March, 2015, 08 : 00 AM [IST]

Venkatesh Ganapathy

Whether refined or not, all oils are sensitive to heat, light, and exposure to oxygen. Rancid oil has an unpleasant aroma and acrid taste, and its nutrient value is greatly diminished.

To delay the development of rancid oil, a blanket of an inert gas, usually nitrogen, is applied to the vapour space in the storage container immediately after production.

This is referred to as tank blanketing. Vitamin E oil is a natural antioxidant that can also be added to cooking oils to prevent rancidification of the edible oil.

All oils should be kept in a cool, dry place. Oils may thicken, but they would soon return to liquid if they stand at room temperature.

Negative effects
To prevent the negative effects of heat and light, oils should be removed from cold storage just long enough for use.

Refined oils high in monounsaturated fats keep upto a year (olive oil would keep upto a few years), while those high in polyunsaturated fats keep upto about six months.

Extra-virgin and virgin olive oils keep upto at least nine months after opening. Other monounsaturated oils keep well upto eight months, while unrefined polyunsaturated oils keep upto about half as long.

Longer shelf lives
In contrast, saturated oils, such as coconut oil and palm oil, have much longer shelf lives and can be safely stored at room temperature. Their lack of polyunsaturated content causes them to be more stable.

Let us take the example of soyabean oil. It is commercially sold in the markets as cooking and salad oil. It is also used in such products as margarine and shortenings.

At stores, consumers must opt for fresh oil, especially packed in containers, since soyabean oil, which is high in poly-unsaturated fats, tends to undergo early oxidation on exposure to air, light and moisture.

Commercially-available oil is often fortified with vitamin E and oleic acid (mono-unsaturated fatty acid) to improve its nutrition profile.

At home, the unpacked oil must be stored at room temperature in a cool dark place, and small amounts of it must be transferred to a dispensing bottle for daily use.

Cold storage facility
At places where the average day temperature exceeds 25 degrees Celsius, it should preferably be stored in a cold storage facility.

But a fresh stock of edible oil must always be bought.

Air, heat, light and age affect the quality and shelf life of many types of edible oils, which deteriorate through oxidation (rancidity).The oxidation process is greatly enhanced when edible oils are stored in containers that are not air tight and in areas where the oil is exposed to heat and light.

If improperly stored, some oils can easily take on other flavours. An unpleasant smell or taste indicates that the oil is no longer desirable for consumption.

The smell or taste of wine may reveal that the oil was not stored properly. A metallic flavour would indicate that the oil was stored in a container made with reactive metal. If edible oils become rancid very quickly, it may indicate that the oil was improperly stored and has oxidised.

Most unrefined oils (oils obtained by the cold pressing and mechanical methods) would keep for between three and six months, if properly stored in a cool dark location.

The refrigerator is the best place to store unrefined oils, and although most would solidify in the colder temperature, they would return to a liquid state if removed from the refrigerator one or two hours prior to use.

Refined oils (oils obtained from heat and solvent extraction) tend to keep twice as long as unrefined oils (between six months and a year, if stored properly).

Oils high in polyunsaturated fats have shorter shelf lives than oils high in monounsaturated or saturated fats, and should be stored in the refrigerator to extend their shelf lives.

Ghee
For proper cold storage of edible oils, the sufficient floor space that facilitates the easy movement of goods is needed.

What is also needed is a state-of-the-art locking system and sufficient lighting points with uninterrupted power supply.

Generally the storage temperatures range between zero degree Celsius to 10 degrees Celsius, and sometimes, edible oils are stored up to minus 20 degrees Celsius. Many cold storage facilities have digital temperature displays.

Generally, consumers should carefully consider their cooking oil requirements before purchasing five- or ten-litre edible oil packs, just because they are being offered at substantial discounts.

Guidelines for storage of solid fats
Most solid fats are from animal sources. However, there are exceptions.

Tropical plant oils, such as coconut oil, are either solid or semi-solid at room temperature, and vegetable shortenings and margarine made from plant oils are solid due to the hydrogenation process.

Most solid fats also contain a higher degree of saturated fat than liquid fats, and therefore, are very stable and tend to keep for extended periods, especially when refrigerated.

Clarified butter
Although clarified butter keeps longer than whole butter due to the removal of the milk solids, homemade clarified butter should be refrigerated in case any milk solids are still remaining in the finished product.

Refrigeration would allow clarified butter to remain useable for an extended period.

Coconut oil
Coconut oil is either solid or semi-solid at room temperature due to its extremely high saturated fat content, and, therefore, is resistant to rancidity.

It can be kept in its container in a cool dark cabinet for many months, and can also be stored in the refrigerator, where it would keep for an extended period.

Ghee
Ghee, which is usually sold in cans, does not have to be refrigerated because it contains no milk solids that would get spoiled.

What is special about olive oil?
Olive oil can be kept longer than most other edible oils. Although it can get rancid, olive oil is less likely to become rancid than other oils, especially if it is stored properly.

The best containers for storage are glass (especially tinted glass), ceramic, porcelain, or non-reactive metals, such as stainless steel.

Olive oil would oxidise rapidly if it is not kept in a sealed container. If it is stored in a bottle, its cap must be replaced and it should be kept tightly sealed. The oil should never be put in a container that does not have a tight cap or some other method of sealing.

It should not be stored in containers made of reactive metals, such as copper or iron. The chemical reaction between the oil and the metal will damage the former and may produce toxins. The oil should not be stored in plastic containers because it may absorb PVC from the plastic.

The ideal temperature for storing olive oil is 57 degrees Fahrenheit, although a normal room temperature of 70 degrees Fahrenheit works very well if the olive oil is stored in a dark area where the temperature remains fairly constant.

It would solidify at 36 degrees Fahrenheit, but it would return to a liquid state as soon as the temperature rises. In colder weather, olive oil may turn cloudy, especially if the temperature of the storage area falls below 50 degrees Fahrenheit.

It is important to store olive oil in a cool, dark place. A wine cellar is an ideal place for storing it, because it is dark and the temperature is cool and constant. Since most of us do not own wine cellars, a kitchen cabinet located away from the stove and direct sunlight would work quite well.

Refrigeration would extend the life of olive oil without harming it. It may become cloudy and solidify in the refrigerator, but that would not significantly affect the quality or flavour.

When the oil is warmed to room temperature, it would return to a liquid state, and its colour would be restored.

Refrigeration does not harm most grades of olive oil, but it is not recommended for expensive extra virgin varieties because condensation may develop in the bottle, affecting the flavor.

Preservation of cooking oils
A carnosic acid-rich extract from rosemary may extend the shelf-life of sunflower oil, and perform better than synthetic preservatives. This was stated by a new study.

Antioxidants are used to preserve edible oils, but the dosage of antioxidants is important.

Oils and fats, and foods with a high oil or fat content, are susceptible to deterioration through oxidation. The objective here is to preserve the quality by avoiding oxidation.

Oxidation refers to a chemical reaction where atmospheric oxygen attacks the fat acid chains of triglyceride molecules.

The oxygen attack can take place at ambient temperatures or below (i.e. during normal storage of oils or finished food products).

It can also occur at elevated temperatures, such as during processing or deep-fat frying.

In order to protect the oil and improve oil stability, oxygen should not come in contact with the product at any stage of the production process.

In line with the worldwide trend towards the replacement of harsh physical and chemical preservative methods with less severe alternatives, the food industry is increasingly relying on nitrogen to resolve the oxidation challenge.

Nitrogen is a chemical element. Because it is an inert gas, it does not interact directly with the product.

It is used to displace atmospheric air (and thus oxygen) and water vapour to avoid oxidation.

There are two main processes for replacing oxygen with nitrogen - sparging to remove the dissolved oxygen; and blanketing to assure the absence of oxygen in the headspaces.

Cooking oil storage and preservation in pantries and industrial canteens
Cooking oil is a staple in most pantries, and is used frequently by chefs of households to prepare any number of culinary variations.

The preservation of cooking oil is often overlooked until one goes to pour a spoonful into a pan and it smells, looks (or tastes) offensively malodorous.

Such rancidity often goes unnoticed for some time because most oils bought at a store are highly refined and deodorised; but aside from the taste factor, rancid oils present significant health risks such as heart disease, atherosclerosis, and cancer.

Clearly, this should be avoided at all cost by ensuring that cooking oils are stored properly from the time they leave the store.

The cause of rancidity is oxidisation, an inevitable process due to the exposure of a fat or oil to air, heat, and light.

The more polyunsaturated a fat is, the faster it would go rancid.

Examples of oils with a high polyunsaturated fat content are flaxseed oil, sunflower oil, corn oil, and soybean oil.

Butter, palm oil, and olive oil have relatively small amounts, but they are by no means safe from early rancidity if not handled with care.

In general, unless cooking oil has been specially preserved, an unopened bottle has a shelf life of about a year if it has been properly stored. Highly polyunsaturated oils don’t keep as well.

Although an active chef may go through a large quantity of cooking oil, the average person should avoid buying in bulk.

The shelf life of cooking oil should be accounted for while shopping. Like other food items, products tend to be fresher at stores with a higher inventory turnover rate.

Mind the expiration date, too. Provided that cooking oil is fresh at purchase, those with more preservatives added by the manufacturer last longer than those without them.

Also, while darker-coloured oils tend to be more flavourful than paler-coloured ones, it is important to note that ingredients contributing to the flavouring and colouring of the product also lead to faster rancidity.

Thus, for maximum shelf life, a consumer should always buy paler-coloured oils. The bottling of the product is also important, as some bottles are more gas impermeable than others.

Opaque glass best
The most preserve-friendly package for the product would be an opaque, airtight glass or metal container.

Some people don’t like to buy a product simply based on its bottling. If you don’t, the solution to meeting your product of choice with smart storage is to transfer the cooking oil into a different bottle when you get home.

If the oil comes in a plastic container, particularly clear plastic, then it’s a good idea to transfer it to a gas impermeable glass or metal container that can be sealed airtight.

It is thus important to refrigerate stored oil, especially after it has been opened, and to keep transparent glass and plastic containers stored in a dark place such as in a box to avoid speeding up the oxygenation process.

A lower temperature may cause the cooking oil to become cloudy or solid, but in fact, the fat is still perfectly usable and would return to its normal liquid, clear state once left out before use and warmed back to room temperature.

Thus, the proper storage and preservation of cooking oils is essential to ensure that we consume quality cooking oil.

It may be expensive to buy cooking oil frequently, but if you consider the trade-off, it is a much better option.

It is better to consume quality edible oil than a cheaper oil of sub-standard quality. After all, health is wealth.

(Venkatesh Ganapathy completed his B Tech [Oil Technology] from UDCT, Mumbai, and obtained a masters’ degree in business administration [MBA] from Southern New Hampshire
University. He currently works as associate professor (marketing and operations) at Presidency School of Business, Bangalore. He can be reached at Venkatesh_gana@yahoo.co.in)