A buyer's guide to cooking oils
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Oils or fats (known collectively as 'lipids) have formed the basis of our cooking since man discovered how to render animal fat from whatever beasty he had on a spit over a fire. We use it not only for flavour (I'm thinking dripping on toast, goose-fat roast potatoes, duck-fat chips, walnut or hazelnut oil drizzled over a salad) but also as a general cooking medium (regular olive oil, sunflower, vegetable or my flavourless preference, groundnut). Oils are all around the same calorie mark, at about 100 calories per tablespoon; they do different things inside you, though - some helping to lower cholesterol and some building it up.
There are now squillions of different types of oils available on the market. Here's my guide to the most common ones - it's a quick-start guide - flavour characteristics, uses, smoking point and a bit of health stuff too!
Extra virgin olive oil
Made from the first pressing ONLY of the olives; flavour varies from mild to peppery; use on salads and try not to heat as this can destroy part of the flavour; high in mono-unsaturated fats which have been shown to reduce the risk of heart disease; a good quality extra virgin olive oil (called 'EVOO' on many websites these days) will have a relatively high smoke point (just under 200°C). Store it in the dark to preserve its flavour.
Regular olive oil
As above but better for cooking as it is less expensive and has less nuances of flavour.
Groudnut aka peanut oil
Flavourless oil made from peanuts; great for bulk use where flavour would be a negative - ie in sauces such as mayonnaise or Asian vinaigrettes; also great for frying and particularly popular in the US for french fries. Its smoke point is around 230°C, one of the highest of any oil, making it very useful for frying. It is free from cholesterol making it one of the better oils for you.
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Good quality extra virgin olive oil should be reserved for salad dressings.
Relatively low in flavour, this oil is made from pressing sunflower seeds and is inexpensive so useful for deep frying, although I find it a bit more pungent than something like peanut. It has quite a high smoke point at 227°C. Great for when flavour isn't essential - deep frying or stir-frying or in oil-based cakes like carrot cake. Research tentatively suggests high consumption levels can cause cancer so perhaps one to avoid.
One of the finest food stuffs in the world; rich, flavoursome, unctuous and great for cooking, adding roundness and depth. Made up of butter fat, water and milk proteins and derived from churned cream, a very 'pure' fat but one that isn't particularly good for you due to the concentration of saturated fat (around 60%) which isn't good for the heart. Smoke point is 120 to 140ish, but this low smoke point allows us to make 'beurre noisette' or burnt butter, the delicious sauce frequently served a smattering of capers over fish.
This fat is used most frequently in Indian cooking and is clarified butter, made by heating butter and causing the milk solids to separate from the butter fat. The top layer is poured off to create ghee and the solids discarded. A high smoke point of 250°C makes it a versatile fat for both frying and deep-frying. The problem with ghee is that it is not strictly a 'bad' fat - in low doses it can actually help to lower cholesterol but in the large amount that is used in many Indian restaurants, it isn't a healthy fat.
I've grouped these together because of their similar properties; they both make wonderful dressings for salad leaves but have relatively low smoke points (around 220°C and 160°C respectively) and their delicate nut flavours disappear quickly. Walnut oil has a long list of health benefits - not least of which is that it contains free-radical fighting antioxidants.
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Oils with a high smoke point like groundnut oil, are suitable for stir-frying.
There are two types of sesame oil - toasted and untoasted. The untoasted variety has a very delicate flavour. Toasted should be used as a drizzling oil not a cooking oil, as it frequently is. It burns incredibly easily and overpowers all other flavours. 180°C is roughly the smoke point - way lower than your wok will be when you make a stir-fry. Try to find untoasted variety - it is light and deliciously nutty. The oil is made from pressing sesame seeds and it should be used quickly as its flavour will not last. It ranks close to olive oil in its health benefits.
This oil has a beautiful golden colour and is great for salads and cooking. It is related to canola oil and has a very high smoke point - certain varieties will smoke at around 245°C. You can get cold-pressed varieties which are better (and more expensive). It contains half the saturated fat found in olive oil.
A relative newcomer to the oil scene, this is derived in a similar way to the olive - not from the stone but from the fleshy pulp around the stone itself. It is high in both mono and polyunsaturated fats making it a good choice and is also good for your skin; it has a very high smoke point of around 270°C which is amongst the highest of all the oils. You can use it as you would an olive oil, for pouring or in salad dressings - it is a beautiful deep green colour which looks fantastic drizzled into a soup.
Lard/dripping/goose fat/duck fat
Not strictly an oil, but hey -these are packed with flavour and have lots of uses from frying your fried bread or an egg for brekkie to gorgeous chips and roast potatoes. I've even used goose fat to make a brownie. It was... interesting to say the least. There is plenty of controversy around their use due to health reasons - but certain varieties, ie Iberico pork fat, are actually better for you than butter as they contain less saturated fats. The smoke points of these oils vary but can get up to around the 220°C mark.
A couple of pointers - oil changes structure when it is heated making it, generally, less healthy. It does, however, impart a better flavour - but only up to a point. Store all your oil in the dark with a lid on - exposure to oxygen will cause oxidisation and rancidity, making everything you put it in taste horrid! Above all, treat your oil well and consider how you use it, the volumes you are using it and what you are using it for. But don't deny yourself - there's nothing quite like hot toast with lashings of butter...