Johanna Hignett reviews the functional roles of fats in food, including which fats are best for specific types of cooking, as well as storage advice and tips for choosing healthier fats
Fat is one of the main nutrients in the diet which should provide around a third of our energy. It’s also a source of the fat-soluble vitamins A, D, E and K. Intakes of fat have declined in recent years and total intakes are now close to recommended intakes. Unfortunately, the same can’t be said for one of the types of fat, saturated fats, where our intakes remain high. Ideally, we should be swapping saturated fats in our diet for unsaturated where we can.
Here we take a slightly different look at fats, reviewing the functional roles of fats in food, discussing which fats are best for specific types of cooking and considering options to swap fats to improve health aspects.
Fats can be divided into two categories based on appearance: solid fats and oils. At room temperature fats such as lard, butter and ghee are solid whilst fats from olive, sunflower, corn and nuts are liquid or oils. Typically, saturated fats are solid at room temperature whilst unsaturated are oils, though processing techniques enable oils to be hardened to give us solid and spreadable fats. The simple fact of whether a fat is solid or liquid at room temperature can have a major impact on its functional role and use in different cooking methods.
Oils are 100% fat, but the fat content of solid fats varies quite a bit. Spreadable fats range from 45% fat through to 80%, whilst block butters are around 80% fat and butter based spreadables slightly less. ‘Light’ spreads vary too from 30% fat up to 49%, whilst lighter butters are around 57% fat. It can be a little confusing, but the trick is to read the information on the label.
Water is added to spreads to reduce the fat content, so lower fat spreads have a higher water content which affects their use in cooking. For instance, they are great for spreading but not ideal for pastry making. If you’re making cakes or biscuits using the creaming method, margarines are great – you will find the one you prefer!
The main uses of oils in the kitchen are for frying or sautéing food or blending with other ingredients to make dressings and sauces including mayonnaise.
Frying takes place at temperatures in the region of 180-190oC and food placed in oil at this temperature loses water as steam from its surface forming the familiar crust seen in fried foods.
The hot oil transfers heat to the food, cooking it through and providing the characteristic colour, flavour and texture of fried food. The extent of the changes depends on both the temperature and time used for cooking; longer periods in hot oil form darker crusts such as in deep fat frying. Temperature is particularly important, as frying food at a temperature which is too low results in an increased uptake of fat and often greasy soggy food!
Cooking oils must be stable at the higher temperatures used during the cooking process. Certain types of oils are more suited to frying and key to determining the suitability for frying is the ‘smoke point’, or the temperature at which an oil starts to break down, burn and smoke and becomes unsuitable for frying. Oils such as unrefined vegetable oils and extra virgin olive oil have lower smoke points and are less suitable for deep fat frying, where temperatures are higher. Oils such as refined corn and sunflower oils with higher smoke points are better choices for frying.
Repeatedly heating the same oil for frying (as might be the case in deep fat fryers) is known to darken its colour, increase the oxidation of the fat and potentially lead to the development of undesirable compounds. Unsaturates, particularly polyunsaturates, tend to be less stable, but the simple solution is to regularly discard old oils and renew with fresh vegetable oil. In fact, EUFIC recommend changing oil after every 10 fries.
Fats that are suitable for baking items such as cakes, biscuits and pastries have different technical properties to those suitable for frying. The principal difference is that they are hard at room temperature. The structure of hard fats enables them to combine with other ingredients such as flour or sugar helping to produce the textures that make up pastries, biscuits and cakes.
- Rubbing in – rubbing fat into flour coats flour particles, preventing water absorption thus giving the short crumbly texture found in pastry and biscuits on cooking.
- Flakiness – fat can also separate a pastry dough into layers on baking giving a flaky and crumbly texture such as in flaky and puff pastry.
- Creaming – whisking fat with sugar incorporates air helping to produce a soft spongy texture when baked, as in a cake.
- Colour – fats can also impart colour to a baked product. Margarines and butters give a yellow colour whilst shortening, such as lard, remains white or pale.
Oils to fats
The technical properties of oils limit them largely to use in frying, roasting and salad dressings whilst hard fats are more suited to baking purposes.
Oils can be hardened to produce vegetable oil-based fats that are suitable for baking too. This process is called hydrogenation and produces harder fats that we can use for spreading and baking. It also enables fats with lower levels of saturates and higher levels of unsaturates to be selected where traditionally fats with higher levels of saturated fats were used.
Storing fats and oils in the kitchen
Fats are susceptible to degradation, and when they spoil they become rancid. Oxidation of fats (which can be speeded up by exposure to light, heat and air) causes fats to become rancid, giving an unpleasant flavour and aroma. Storing fats carefully can help to avoid this occurring.
Oils should be stored at room temperature in a darker cupboard to avoid prolonged exposure to light, which may promote oxidation and as some can harden if kept too cool. Hard fats should be refrigerated but may need returning to room temperature if being used for the creaming method or cakes.
Checking nutrition labels to find fats with lower levels of saturates is a great step when choosing fats for cooking, and don’t forget that fat is an energy dense nutrient so keeping an eye on the amount of higher fat foods we choose will help us manage our health too.
References available upon request.
Johanna Hignett, Nutrition Consultant (RNutr), is a highly experienced nutritionist with over 20 years’ experience working primarily as a nutritionist in the food industry, as Head of Nutrition Science and Communication for Nestle UK before setting up Nourish Consulting over ten years ago.