Authors: Joanna Blythman
There were mutinous mumblings in some quarters. Bored with recycling the same old scary story about how ‘sat fat’ (now abbreviated for speed of demonization) was killing us in droves, magazines eventually turned to quirky exceptions, notably the ‘French paradox’. This term, coined by Dr Serge Renaud, director of public medical research at the French National Institute of Health and Medical Research in Lyon, captured the apparent contradiction that the French had a relatively low incidence of cardiovascular disease despite eating a diet rich in saturated fat. His observation was warmly received in food-loving, food-literate France; some years later he was awarded the Légion d’honneur. But in common with all those who dared to question the anti-sat fat dogma, Renaud’s research was dismissed as dangerous heresy in other countries, especially those of a Presbyterian inclination, and the evilness of saturated fat was zealously propagated. This entrenched dogma was repeated so assiduously that it became the key fact that even the least nutritionally educated members of society had absorbed. Hard fats = bad fats. Liquid oils = good fats. That was all you needed to know.
Seeing how the nutritional script was unfolding, food manufacturers dropped solid saturated fats faster than a flaming chip pan, and switched production to oils rich in polyunsaturates, such as corn, soy, safflower, sunflower and oilseed rape. The dietetic fatwa on saturated fat was good for their bottom line: polyunsaturated oils were, and still are, much cheaper to buy than saturated fats. But they did have a downside. Unlike saturated fats, which are stable at room temperature, keep reasonably well, and are fairly tolerant of being heated, polyunsaturated oils are highly susceptible to deterioration. Light and heat have a devastating impact on their more sensitive chemical structure.
So although using vegetable oil high in polyunsaturates has been widely seen as a healthy choice, this is only half the story, as one oil company executive explains: ‘If you heat it up, then you degrade it and create much more reactive substances than monounsaturated [the predominant fat in olive oil and many meats] or saturated fat.’
In an attempt to make polyunsaturate-rich oils more stable, oil suppliers adopted a technique known as hydrogenation, which had been developed for hardening soaps. Liquid oils were heated and combined with hydrogen atoms using a nickel catalyst. These oils, referred to as partially hydrogenated, did the job that manufacturers needed done. Hydrogenation acts as a preservative. The hardened oils stay fresher longer, giving products an accommodatingly long shelf life. Partially hydrogenated vegetable oils and fats became the mainstay of the processed food industry, for everything from margarine, salad dressings and sauces to pre-cooked chips, chicken nuggets, crisps and fish fingers.
Under pressure from the anti-sat fat lobby, fast food companies followed suit, bragging about their change to heart-healthy oils. The oily slide to jettison saturated fats even trickled down to chip shops. Where previously beef dripping had been the fat of choice, ‘we fry in vegetable oil’ banners appeared in windows. It seemed like a forward-thinking change to make, as one Scottish fish and chip shop owner recalls:
I was aware of the reputation of fish and chips as an unhealthy food, so I thought, ‘Let’s try something different’. I decided to promote the change as a benefit, so I advertised in the local press that I was using an all-vegetable product, which was healthier. I did lose two customers who were diehard dripping users, but I gained so many people who wanted to try a vegetable product that my business has grown by 25%.
By the 1990s, however, the bad news about partially hydrogenated oils was seeping out, rather like a greasy stain that calls for a fresh change of clothes. It emerged that hydrogenation created ‘trans fats’, and these man-made fats were pretty deadly. Following the release of several scientific studies showing that eating trans fats increased the risk of developing heart disease, stroke and type 2 diabetes, health advocacy groups in the USA started campaigning for the food industry to remove them from their products.
At first, industrial food companies were in denial, hoping that these unsavoury revelations would melt away. They didn’t. By 2002, the US government acknowledged for the first time that there was no safe level of trans fat, and that people should eat as little of it as possible. By 2006, it was mandatory to list trans fat on US food labels. Come 2010, reducing intake of trans fats was a key recommendation of the Dietary Guidelines for Americans. In the UK, the FSA took no such action, justifying its inaction on the basis that manufacturers were voluntarily removing trans fats from their products. In commercial terms, although they still linger on in products such as crackers, biscuits, cakes, frozen pies and frozen pizza, microwave popcorn, coffee creamers, and ready-to-use frostings, the writing is on the wall for trans fats on both sides of the Atlantic.
So in an echo of the flight from saturated fats, manufacturers who value their reputation have dumped, or are in the process of dumping, trans fats. Faithful to the anti-sat fat dogma, they continue to use polyunsaturate-rich oils, but now choose only the unhardened, non-hydrogenated sort – but this presents them with a number of technical challenges. Essentially, the less saturated fat is, the less stable it is, so non-hydrogenated oils are something of a nightmare to work with. ‘For me, the biggest issue in frying today is the incorrect use of polyunsaturated oil for deep fat frying’, says one oil company executive. ‘It’s pretty cheap. The downside is – and people don’t realise it – it goes off faster [than saturated fat].’
So how does it ‘go off’ exactly? The first obvious consequence is flavour. When polyunsaturated oil degrades it quite quickly develops a distinctive taste and aroma that oil experts refer to as ‘fishy’. If you have ever reheated deep-fried factory foods, such as hash browns or onion bhajis, that description might evoke some memories.
The next problem is that polyunsaturated oil builds up gunk, as this chemical company advice service explains:
Over the past decade, as foodservice operators and food manufacturers have eliminated trans fats from their menus and food products, they have experienced some unexpected consequences from their use of zero trans fat oils. One such consequence is polymerisation, which causes gunk to form a coating on frying and manufacturing equipment. Polymerisation also can leave a film on kitchen and front-of-the-house surfaces that is both difficult and costly to remove.
Polymers are in the mist of oxidised fat that comes out of the deep-fat fryer, forming a sticky, varnish-like deposit on everything around – walls, work surfaces, utensils, workers’ hair and clothing. Most of us will have inhaled polymers in takeaway and fast food restaurants, or from the heavy, smelly air that hangs around outside them.
A further problem is that aldehydes, the breakdown products from polyunsaturated fats, are much more reactive – so in effect, trouble-causing – than those of either saturated or monounsaturated fat. In fact, the toxicity of these aldehydes is well established in scientific literature: ‘The geno- and cyto-toxicity of these latter compounds [aldehydes] is well known and they have recently been thought to be responsible for several diseases, such as cancer, Alzheimer’s and Parkinson’s’, one recent study concluded. We can ingest aldehydes either directly from the degraded oils by inhalation – a particular occupational hazard for factory workers – or by eating foods fried at high temperatures.
In a nutshell, although food manufacturers are gradually eliminating killer trans fats from their products, the polyunsaturate-rich vegetable oils they rely on still represent a Pandora’s box of problems. Seeing trouble looming, suppliers of oils are now marketing a new wave of polyunsaturate-based vegetable oils that, wait for it, are said to have a healthier profile than their predecessors. Is this beginning to sound familiar?
The sales pitch this time round is that these latest oils are high in oleic fatty acids, also known as Omega-9s, (the dominant fat in olive oil), and lower in linolenic acid. The latter has the bad habit of decomposing during deep frying into acrolein, a pungent, possibly carcinogenic aldehyde compound that irritates the eyes and respiratory tract. ‘Omega-9 oils are the next generation in healthier oils because of their unique health profile’, Dow AgroSciences assures us. ‘Our oils allow the foodservice and food processing industries to reduce ‘bad’ (trans and saturated) fats and increase good’ (monounsaturated and polyunsaturated) fats in food products, making healthier options more readily available.’ Déjà vu. Back to the script we have learnt by rote, that now familiar binary opposition between killer and saviour fats, and yet again, the actors playing the roles have been changed.
Still, surely anything that makes cooking oil more like olive oil has to represent progress? Sadly not. While the oleic acid in olive oil may be perfectly life-enhancing when it is anointing your mozzarella, tomato and basil salad, it behaves quite differently when heated up for deep frying. To be more specific, it produces breakdown products – oxidised monomeric triglycerides – that are absorbed in the human stomach and intestinal tract. These have been linked to cardiovascular disease and type 2 diabetes.
Of course any oil, however virgin and healthful at the outset, will come a cropper with overheating, and this is true whether you are frying in a domestic kitchen, a takeaway, or in a factory. The longer the oil is in use, the greater the presence of undesirable breakdown products. But in home cooking, oil is generally used once or twice, then discarded. On a factory scale, oils are used intensively over and over again, typically for anything from 7 up to 12 days; and remember that many food processing factories work round the clock. As one industry observer notes:
In a commercial [factory] setting, it’s a wonder that oils survive at all considering the ways in which they are abused. Large surface areas of industrial fryers expose the oil to air and oxidative stress. Accumulation of crumbs from cooked food further abuses the oil. High temperatures used in frying break down oil faster.
Food manufacturers often rely on methods as crude as colour change, or a weekly schedule, to determine when to change frying oil. Up-and-coming high oleic acid oils give them a lot more leeway because they hold up longer at higher temperatures, as one advocate for their deep-frying potential points out:
These higher smoke-point [high oleic acid] oils extend use of frying oil without sacrificing taste or performance. Not only does this help maintain a consistent product, but fewer oil changes mean savings on labor and on the oil itself. Some high-oleic soybean oils can extend fry life two to three times longer than conventional versions.
Clearly, oils have to be tough as nails to withstand the rigours of commercial-scale deep frying. And in this respect, you can forget those produced by quaint traditional extraction methods, such as cold pressing; that’s sissy stuff. Food manufacturers need battle-hardened marines that have survived an assault course even before they get to the factory.
This is why the oils that are destined for factory frying and fast food use are known as RBD, short for refined, bleached and deodorised. They owe their neutral flavour and prodigious keeping quality to a thoroughly industrial refining process. The oil seeds are crushed, and the oil is extracted using solvents, usually hexane. More chemicals are used to remove most (although not all) of the solvents; residues do remain. By this point in the refining process, some gummy stuff will have appeared in the oil, so it needs to be degummed, with the aid of either acids or enzymes. Hot by this point, the oil doesn’t smell so good and will have darkened in colour, so it then has to be bleached using clay. Next up, it must be deodorised, which means heating it to a very high temperature at least twice. Put it this way, the RBD process produces oils that are hot and bothered, the very opposite of cold, unruffled and artisan.
Of course, when we buy cheap refined vegetable oil for home frying purposes, these are also RBD oils, but at least home cooks don’t add anything further to them, unlike food manufacturers. To get the maximum longevity from their oils in the deep-fat fryer, food manufacturers and fast food outlets can add a number of ‘improving agents’ that extend the ‘fry life’, that is, delay the chemical degradation of the oil. First on the list of possibilities are antioxidants, basically preservatives by another name, such as citric acid, gallates, TBHQ (tert-butylhydroquinone), which is also used in varnishes and resins, and BHA (butylated hydroxyanisole). This last item ‘is reasonably anticipated to be a human carcinogen’. It usually comes in a solution of propylene glycol (antifreeze) and is wonderfully user-friendly because it ‘remains colourless even when heated at 194°C for one hour’. Next, an antifoaming agent might be added, such as polydimethylsiloxane (a type of silicon), along with an anti-spattering agent, such as lecithin. An emulsifier, such as mono- and diglycerides of fatty acids, can also go into the blend. Most commercial-scale fryers will also use mineral filters, such as silica, bentonite and perlite, to slow down the build-up of tacky, sticky deposits. As you will appreciate, there’s more in industrial cooking oil than just straight oil, yet none of it appears on the label of the finished fried product – your packet of tortilla chips, your doughnut, your chicken Kiev – because they count as processing aids, not additives.
Another long-life frying medium coming into the frame for food manufacturers is EE – extruded expelled oil, usually from soya. More expensive, and still a minority choice, at first view it looks like a less chemical alternative to RBD oil. The oil seeds are squeezed through small metal holes, under high pressure and high temperature. But its main appeal to food manufacturers and fast food restaurants appears to be that it offers an exceptionally long fry life. As one US chef noted: ‘We had been changing our frying oil every five to seven days. Suddenly we were able to go 12–14 days using the new [EE] oil.’