Catherine Brown goes in search of the best oils to pep up your summer salads and gets some expert advice on how to taste test the slippery stuff

Pouring oil in a thin stream over mixed salad leaves has become a mealtime ritual these days. But which oil? They all perform more or less the same function of lubricating the leaves so it's on taste, food value, and price, that we must make our choices. Lurking in the corner of the chill cabinet, in my neighbourhood wholefood store the other day, was a bottle of

Elmer's Original Pure Hemp Oil. Interesting. Expensive, though.

But how did it taste?

''It has a wonderful taste,'' replied the assistant. ''It's quite intense though. So you don't need a lot of it to get the flavour.''

''Is it fruity then, like olive oil?''

''No it's got a lovely mellow nutty flavour. It's also got a higher level of essential omega fatty acids than any other plant.''

Sure enough, 85% (omega three, six and nine) it said on the label. It also said ''store

in the refrigerator'' for the oil's omega fatty acids are particularly sensitive to heat, light and oxygen.

These valuable fatty acids are believed to inhibit the production of harmful cholesterol, dilating blood vessels and preventing the clotting of blood platelets in arteries, as well as reducing blood pressure. My oil (bottled by Naked Earth, PO Box 996, Kingston-upon-Hull, HU8 8YT) said on the label that it

came from an ''extra virgin'' cold pressing

and had been made from organically-grown

hemp seeds.

The confusion between industrial hemp, which has been grown for centuries for paper, fibre, food and fuel, and the plant's use as a narcotic, surfaced recently when Body Shop founder, Anita Roddick, launched a new range of hemp skincare products.

Handing out packets of cannabis sativa seeds to people, as part of the publicity launch, they came with a drugs warning: ''Do not attempt to use the plant as a narcotic. You would need to smoke a joint the size of a telegraph pole to get high.''

She would like to see the use of industrial hemp restored - it can only be grown in this country with a Home Office licence. But it's an environmentally-friendly, easily-grown and versatile natural product. We need to think of it differently, she says, and not just as a source of drugs.

The sight of a hemp plant is not going to drive the country's youth to drugs, just as Poppy Day is not going to encourage them to take opium. If it became legal to grow industrial hemp again in the US, where it has been banned, hemp oil could become as common as corn oil and much better for us.

But until that happens we must look to other sources of good flavours to oil the salad. To the oil from the olive which leads the market. Produced only in warm, Mediterranean climes, it has found its most lucrative market in colder northern countries where many myths and confusions about it still exist. Most widespread - to the advantage of the producer rather than the buyer - is when it is priced higher than its worth.

An expensive bottle of oil does not always guarantee a better quality. So far the olive oil industry has not produced a clear definition that we can trust as a benchmark of quality.

Too many commercially-blended extra virgin olive oils are of an indifferent quality. They often have none of the fruity aromas, and tastes of ripe olives, which should be there. The Italians get the blame for producing the largest amount of indifferent extra virgin olive oils, while the Spaniards and the Greeks are usually credited with producing a better quality at a cheaper price.

Then there is the fancy bottle market (usually Italian), sometimes with spices and herbs added. They provide an amusing diversion, but there is no guarantee that the oil inside is equal to the price paid. To find a value-for-money olive oil, Anne Dolamore, (in A Buyer's Guide to Olive Oil, Grub Street, #7.99) suggests that you buy in the smallest quantity you can. Then do a critical tasting of the oil on its own to establish its worth.

Put a few tablespoons into a wine glass. Hold the glass in your hands for a few minutes to warm the oil slightly and release the aromas. Then ''nose'' it as you would wine. Take a sip and let the oil slide onto your tongue. After a few seconds, form your tongue into a spoon shape and position it towards your top teeth. Open your mouth slightly and inhale three times in quick succession. The mixture of oil and water will spray your mouth and palate, allowing you to register the sensations and flavours.

Next, swallow the oil. Bitterness is registered at the back of your throat. Try to store in your mind all the immediate impressions. Is it: sweet? bitter? pungent? delicate? fresh? fruity? spicy? nutty? earthy? strong? Do you like it?

Take a drink of carbonated water, or a slice of apple, to clear your palate and taste it again to reaffirm your first impressions. Dolamore usually gives her palate a rest after six ''tastings''.