The inner life of partially hydrogenated vegetable oil
Flaky. Rich. Dense. Moist. Sinful. Luscious. Indigestible?
As the mince pie season lurches towards its peak, campaigners are warning that nine out of ten pies bought in shops this Christmas will contain artificial fats so harmful to humans that they threaten the lives of 20,000 Britons a year.
Partially hydrogenated vegetable oil, a tasteless shortening used in most mince pies and thousands of other processed foods has been linked to heart disease, stroke risk and a range of neurological conditions including Alzheimer's. One leading academic, only half in jest, referred to it yesterday as "devil's spunk".
A continuing study by the Harvard School of Public Health estimates that eliminating the substance, also known as trans fat, from US diets would prevent 100,000 deaths a year from coronary heart disease alone.
The equivalent figure for the UK is 20,000, according to Oliver Tickell of the Oxford-based tfX (the Campaign Against Trans Fats in Food). And it isn't helped by Christmas.
Only explicitly "all butter" mince pies can be relied on to be free of the artificial fat, Mr Tickell said this week. "And high street bakery pies are just as likely to contain trans as mass-produced ones. Even quite posh-looking ones can have it. It depends purely or simply on whether they use so-called "vegetable shortening" or butter".
Last month Marks and Spencer said it would ban all man-made fats from its own-brand foods from next year. Tesco and Sainsbury's have since announced similar initiatives, and from next month all foods sold in the US containing so-called trans fats will be required to declare this on their labelling.
European vegetable oil producers have complained of "unjustified discrimination" towards some of their products, while last week a US soybean analyst warned that his $16 billion industry could shrink by five per cent at a stroke on January 1st.
The food industry, meanwhile, is scrambling to switch to trans fat-free alternatives such as palm oil and cocoa butter.
None of this is easy. The World Wide Fund for nature claims the habitat of a mystery carnivore on Borneo is threatened by a vast new palm plantation. And none of it would be necessary but for an accident of molecular biology.
Partially hydrogenated vegetable oils contain fatty acid molecules with hydrogen atoms arranged diagonally rather than symmetrically around a carbon core. This "trans" shape (hence "trans fat") appears to baffle the human body, either by fooling the metabolic system into absorbing it as if it were a useful fat, or inhibiting the uptake of other essential fats, or both.
Yet for nearly a century its advantages to the food industry seemed miraculous. Partially hydrogenated vegetable oil takes a cheap and abundant raw material and transforms it into a soft, spreadable fat that was long considered perfect for baking, frying, margarine and confectionary.
It melts in the mouth, literally. In the jargon, it has great "mouth feel". It is also an excellent preservative. A chocolate bar made with partially hydrogenated vegetable oil should taste fresh for 18 months, compared with 30 days for one made with natural fat.
But manufacturing it is not for amateurs, because hydrogen is explosive. In a process patented by Procter and Gamble in 1904, hydrogen is bubbled through vegetable oil in the presense of a granular metal catalyst (usually nickel) in a steel, spark-free pressure vessel at between one and six atmospheres. At the same time, the mixture is stirred and heated to about 180 degrees C for between 15 and 30 minutes.
The longer this process is allowed to continue, the more hydrogenated the oil becomes and the higher its melting point once left to cool. Oil and catalyst are then separated by filtration. The oil is cleaned with a bleaching earth to which particulate impurities stick. The earth is allowed to settle, leaving the oil "the pale yellow colour that customers like", according to Dr Mike Gordon of Reading University's school of food biosciences.
It is then "scrubbed" with heated steam in a 200-degree vacuum to strip out "off-flavours", pumped into tubs, drums and tanker trucks, and shipped to market. The whole process can be squeezed into a plant the size of a three-bedroom house, an industry spokesman said.
In the past two years partially hydrogenated vegetable oil has been removed from dozens of Britain's best-known brands, including Mars Bars and McVitie's digestive biscuits. But finding replacement fats is complex and expensive because the slightest change in taste or texture can put consumers off for life.
It's also hard for consumers to know exactly which products still contain trans fats. Some which declare "vegetable fat" on their packaging do, but in others that fat is trans fat-free.
"What's happening is that manufacturers are removing trans-fats quietly because they don't want people to know there was ever a problem," according to Mr Tickell.
The palm oil industry has benefitted, especially from the looming US deadline, because it is virtually tasteless, solid at room temperature in its natural state, and trans fat-free.
But there is an alternative being pushed by vegetable oil refiners. "It's rather technical and some people might not like it, but I'm a strong supporter because it gives the food industry what it wants and also satisfies health concerns," says Mr Tickell.
This high-tech, zero trans fat holy grail of the vegetable oil industry is full, as opposed to partial, hydrogenation. Using existing technology, the hydrogenation process is simply prolongued until every fatty acid molecule is loaded with as much hydrogen as it can hold and their awkward "trans" shape disappears.
There is a catch: the final product has a high melting point and poor "mouth feel". It has to be softened with yet another catalyst (this time usually sodium) in yet another sealed steel tank, in a process known as inter-esterification. If it catches on it might be time to buy futures in sodium; failing that, try butter.