Oils, vinegars, dressings and marinades

About oils

Unlike animal fats such as butter and lard, which are solid at room temperature, most plant oils are liquid at room temperature. This is partly because they contain a higher proportion of healthy unsaturated fatty acids, which are thought to help to lower blood cholesterol.

Modern methods of oil extraction have increased the availability of high-quality oils. Although many of the definitions traditionally used on oil labels have subsequently become redundant, they're still used as marketing tools.

The term 'cold pressed' (once associated primarily with olive oil but now applied to many speciality varieties) indicates that no form of heating or refining was used during extraction. In general, it signifies quality.

'First pressing' indicates the oil is that released the first time the fruit, seed or nut was pressed. When applied to olive oil, the term 'extra virgin' also indicates the oil is from the first pressing. It additionally guarantees that the oil has an acidity of less than 0.8g per 100g.

The term 'single estate' can be found on highly prized bottles and indicates that the oil was produced and bottled at one named source. 'Early harvest' tends to be applied to olive oil and suggests a greener, more peppery flavour than 'late harvest' olive oil.

Oils deteriorate on exposure to light, heat and air. After purchase, keep them in a dark, cool cupboard. To optimise quality, buy small amounts of oil regularly rather than buying in bulk, and keep the spout or lip of the container clean by wiping it before putting it away.

Choosing oils

The range of oils you need to keep in the cupboard depends on the type of dishes you like to make and whether the oil is likely to be used as a cooking medium or as a condiment.

Premium priced single estate olive oils are best used as condiments rather than for cooking: drizzle them over cooked fish, meat, vegetables, soups and pasta. If you fry with them, their superb flavour will be wasted. Some people like to keep a bottle of 'olive oil' (made from a blend of virgin olive oil and refined olive oil) specifically for cooking. Light olive oils are specially blended to have a subtler flavour; they're not lower in calories.

For chips and other deep-fried foods, you need an oil with a high smoke point. This means it can be heated to a very high temperature before it begins to smoke or break down. Soya oil fits this description and has good keeping qualities. 'Vegetable oil' (a blend of rapeseed, safflower, soya and/or others) is an inexpensive option, but it should not be used for dressings or baking because its flavour is invasive. Groundnut (peanut) oil is excellent for all types of frying and baking, but anyone with nut allergies should avoid it.

Speciality varieties

If you enjoy oriental cuisine, toasted sesame seed oil is essential. Don't use it for frying - sprinkle it sparingly over the food just before serving. Argan oil is the authentic choice for Moroccan-Berber dishes and has a mildly nutty flavour that's delicious in dips and dressings (but it's expensive).

Nut oils such as hazelnut and walnut oil are a luscious, fragrant addition to dressings and baking, but they are also expensive and should only ever be purchased in tiny bottles because they oxidise quickly. Pumpkin seed oil, which is stronger in flavour and colour, has a slightly longer life and brings a rich taste to salads.

Hemp seed oil is attracting much interest as a basic cooking oil, thanks to its high smoke point, optimal ratio of essential fatty acids, and the fact that it can be readily produced in Britain. Rice bran oil is another healthy option for frying. It also has a high smoke point and mild flavour.

Flavoured oils, such as those infused with lemon, chilli, herbs or truffle, are fun to use but less versatile than pure oils. Only buy small bottles of these; otherwise they may go off before you finish them.

It's possible to make your own flavoured oils at home but they must be stored in the fridge and used within a week of making, or preferably on the same day. This is because fresh or damp herbs can carry the spores of Clostridium botulinum, a bacteria that can cause the rare but fatal disease botulism.

Health and oil

Oils and fats are essential components of a healthy diet: they help our bodies digest key vitamins, keep skin and hair in good condition, and ensure that our cells work properly. However it is important to keep consumption of oils and fats at moderate levels because they are very high in calories, and to favour those that are high in healthy unsaturated fats and low in saturated fats.

Saturated fats raise blood cholesterol, which is a major risk factor for coronary heart disease and increases the risk of stroke. Healthy unsaturated fatty acids - polyunsaturates and monounsaturates - on the other hand, help to lower blood cholesterol. Be warned, however: trans-fats, found in the factory-produced hydrogenated vegetable oils used in processed foods, are unsaturated oils that have been made more saturated by a chemical process. Studies show that trans-fats not only raise total cholesterol and the 'bad' LDL cholesterol in the body, but also specifically lower 'good' HDL cholesterol.

About vinegars

It pays to keep a selection of vinegars in the cupboard for cooking as they last almost indefinitely. A rich-tasting variety such as balsamic vinegar or sherry vinegar, plus a versatile, light and smooth-tasting bottle of white wine vinegar or cider vinegar, is a good starting point. If you like fish and chips, or making chutneys and pickles, a bottle of malt vinegar is essential. Add more specific flavours and varieties according to the recipes you like to cook.

Although the word vinegar comes from the French 'vin aigre', meaning sour wine, vinegar is produced all over the world from a variety of liquids. China, Japan and South-east Asia have vinegars brewed from rice wine; in Goa, sap from the coconut palm is used; Britain's traditional vinegars are made of cider and unhopped beer. You can make vinegar fairly easily at home by adding a special form of bacteria known as a vinegar 'mother' (or starter) to wine.

Choosing vinegars

Balsamic vinegar and sherry vinegar are both made by the solera system, which gives an intense, complex flavour. Sprinkle directly over salad leaves, adding nothing else but a little olive oil and salt and pepper. A few drops of balsamic or sherry vinegar added to a frying pan after cooking steaks, chops, sausages or chicken makes a quick, tasty gravy. An aged balsamic vinegar can be expensive but you'll be rewarded with a mild, sweet almost syrupy vinegar.

Wine vinegars, including red, white and champagne varieties, are ideal for vinaigrettes and dressings where you want to incorporate other flavours such as mustard and herbs. They are also the right choice for French sauces and marinades. Herb and fruit-flavoured vinegars are often made with wine vinegar.

For an authentic flavour in oriental dishes choose rice vinegar. White rice vinegar has a sweet, mild taste and is used in rice dishes, sweet-and-sour recipes and pickling. Black rice vinegar is similar to balsamic vinegar and can be used as a dipping sauce, or in meaty braised dishes.

Quality cider vinegar can often be used in place of wine and rice vinegars, but comes into its own as a pickling medium for apples, pears and peaches. Distilled malt vinegar (a clear variety also known as spirit vinegar) is good for pickling, too.

Although not a vinegar, verjuice, the juice of unripe grapes, is a delicious alternative. It has the tartness of lemon juice and the acidity of vinegar without the harshness of either, which makes it a versatile ingredient. Use it as you would vinegar - it's particularly good brushed over grilling meat or used in vinaigrettes.

About dressings

Dressings add complementary moisture and flavour to a dish. They are most commonly used cold for salads, but can also cloak cooked vegetables, eggs and pieces of meat, poultry and fish.

The classic vinaigrette or French dressing is three or four parts oil to one part vinegar, although the ratio can go as high as six parts oil to one part vinegar. Mustard is usually included; you might also add crushed garlic, sugar or honey, chopped herbs, grated ginger, and the zest and juice of citrus fruits. Sauce vierge is a warm vinaigrette dressing that can include garlic, shallots, tomatoes and basil and is typically served with vegetables or fish.

A richer option is mayonnaise, another classic French dressing, traditionally made with vinegar, oil, mustard and egg yolk. These ingredients are carefully combined so that they emulsify to give a creamy-textured cold sauce. Many variations are possible by adding herbs, garlic, citrus and other flavourings.

Caesar-style dressing is another emulsified dressing based on egg, but with flavourings of anchovy and parmesan cheese. Tangy dairy products such as blue cheese, buttermilk and soured cream are popular dressing ingredients in American cooking.

Middle Eastern and Asian cuisines offer exciting alternatives. Replacing the vinegar in vinaigrette with pomegranate molasses gives a sweet-sour dressing ideal for green vegetables and chicken, while a combination of yoghurt, tahini and garlic is delicious with cold boiled potatoes or beetroot.

Miso can be used to add full-bodied richness and creaminess to dressings for Japanese meals, while ingredients such as lime juice, fish sauce, garlic, chilli and coriander will give a healthy yet pungent Thai-style dressing.

Using dressings

Try to match your dressing to all the dishes it will be served alongside, not just to the ingredients it will be coating. A rich, eggy Caesar-style dressing tastes great over crunchy leaves of cos or iron-rich spinach and rocket, but not when they're served alongside a plate of similarly creamy blue cheese pasta.

If you're watching your diet, try recipes based on yoghurt instead of cream or mayonnaise, and explore the range of no-fat Asian dressings that forgo oils for rich-tasting ingredients such as soy sauce, tamarind and palm sugar.

Some salads can be left to stand in their dressing for a couple of hours (these recipes are particularly good for buffets), but when using tender leaves it's vital that the salad is dressed only just before serving, otherwise the leaves will wilt and start to break down.

No matter how delicious your carefully made dressing, try not to drown the salad ingredients with it. The dressing should cling lightly to the salad. There should be no pool of dressing at the bottom of the bowl once the salad is tossed. Also, make sure all the salad ingredients are dry before tossing them with the dressing, so that the excess water doesn't dilute the dressing or prevent it from coating the salad.

About marinating

Marinating is mainly used nowadays to add flavour to a variety of meats, poultry, fish and vegetables, but was traditionally a clever way of tenderising tough cuts of meat while simultaneously enhancing their taste and (in the days before refrigeration) preserving them for a few days.

Usually ingredients are steeped in a mixture of oil and acidic elements such as wine, vinegar, citrus juice or yoghurt, and flavourings such as garlic, chilli, herbs and spices. The acid element helps tenderise the food by unwinding its proteins, while the oil adds moisture (countering the drying effect of the acid), plus some flavour, and assists during cooking.

Marinating is a convenient technique, but does require some forward planning if the recipe requires several hours steeping. It is also important to use non-corrodible containers such as ceramic, glass, or plastic as metal can react with the acids in the marinade and spoil the flavour of the food. Marinating in a plastic freezer bag is ideal.

Laying the ingredients in a shallow container will help ensure the maximum surface area is covered by marinade. Some ingredients, such as whole fish and squid tubes, benefit from being scored with a knife before marinating. If the food is not completely submerged, turn it to coat completely before leaving it to steep and then turn it several times (such as every half hour or hour) during marinating. Watch Paul Merrett's video recipes for Butterflied leg of lamb with sherry and honey marinade, or his Spatchcocked marinated poussin with chilli jam.

Depending on the recipe, the excess marinade might be used as a baste or stock during cooking, or boiled for at least 20 minutes and turned into a sauce to serve alongside the cooked food.

Using marinades

Keep soy sauce, Thai sweet chilli sauce, satay sauce, Chinese oyster sauce, and spice pastes on hand for quickly mixing into marinades. Common store cupboard ingredients that can be employed include honey, mustard, dried chilli flakes, ketchup and Worcestershire sauce. Adding a little bicarbonate of soda to the marinade is a clever Chinese way to tenderise sliced meat.

You need not be exact with timings for marinades, but it's important that fish and other forms of seafood are not over-marinated, otherwise they will start to 'cook' in the acid and fall apart. Ideal times also vary according to the dimensions of the ingredients being marinated: diced chicken or a chicken breast beaten thin with a mallet does not require as long as a whole bird. Large joints and some types of game benefit from being left overnight - or even as long as a few days - to allow the marinade to work. Vegetables have a low protein content and therefore do not usually need more than an hour. Follow the timings in recipes.

Rubbing it in

Rubs are dry marinades that are rubbed directly onto the meat, poultry or fish which are then left to stand prior to cooking. Herbs, spices, salt and sugar are blended in various combinations to produce a wide variety of flavours. Rubs are common in Mexico and the Southwest USA and are often used with quick-cooking cuts such as steaks and fillets prior to grilling, however they can also work well with vegetables such as sweet potato. Because rubs contain no fat, the food needs to be brushed with oil or another fat before cooking to prevent sticking.

Recipes

Mayonnaise by Paul Merrett (video recipe)

Chickpea and tomato salad with tahini dressing by Sophie Grigson (video recipe)

Vietnamese-style chicken salad with lime and chilli dressing by Sophie Grigson (video recipe)

Caesar salad by James Martin

Sizzling rice prawns with black rice vinegar by Ken Hom