Discover the chemistry and history of these everyday kitchen staples

A tub of butter with a knife

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Margarine is a commonplace, yellow spread. But it hasn’t always been … 

Butter and margarine are both solidified emulsions of fats in water; butter is produced from milk, and margarine is produced from vegetable oil. But the science and the history of these two spreads are far more complicated.

Let’s start with butter. It’s made from milk and usually comes from cows. Milk is an emulsion of water, sugars and microglobules of butterfat. These fats are mostly composed of triglycerides: long chains of different fatty acids – all containing carboxylic acids – in groups of three. Butterfat provides fantastic nutrients, but is calorific. So, manufacturers in the UK often use centrifugation to separate butter’s components at high speed and remove a portion of the butterfat before sale.

Turning milk into butter is all about breaking down the chemical forces that trap the butterfat in place. Each globule of butterfat is surrounded by a lipoprotein membrane. Producers separate the fat and the water in cream, then churn it, which physically destroys the lipoprotein barrier between the fats and allows the droplets to clump together. The result is yellow, tasty butter ready to use in cooking, baking or as a spread.

Making margarine

No larding matter

Margarine also originally came from cows – but in a very different way. In 1869, France experienced a butter shortage, and the French emperor Napoleon III (a nephew of Napoleon Bonaparte) needed an easy replacement to feed his soldiers. He challenged all chemists to come up with an alternative to butter made from beef fat. Hippolyte Mège-Mouriès, a pharmacist, won the prize by mixing beef tallow with skimmed milk, creating a white spread called oleomargarine. People found the whiteish colour unappetising, so producers dyed it yellow to resemble butter. Vegetable oil soon replaced the animal fat too. During the early 20th century, the first and second world wars meant butter was in short supply, and the cheaper, easier-to-produce margarine soon replaced butter on shop shelves.

This resulted in a huge network of yellow margarine smugglers, breaking the law to get the spread onto the breakfast table

They asked their politicians to stop the ‘demon spread’ from ruining their livelihoods

Modern margarine’s production requires a little more chemistry. Vegetable oils are liquids at room temperature, so manufacturers alter the fatty acids that form its triglycerides to turn it into a solid. Fatty acids with more carbon–carbon double bonds typically have a lower melting point. Manufacturers therefore use a process called hydrogenation – passing hydrogen gas through the oil in the presence of a nickel catalyst – to break some of the double bonds, saturating the chains with hydrogen and increasing the melting point. The problem is that saturated fats aren’t as healthy for us as unsaturated fats, so it is a balancing act to break the right number of double bonds. 

Yellow market

Today, the two rival spreads are available in virtually every supermarket in the world, but it hasn’t always been the case. In the US, dairy farmers almost immediately became worried people would stop buying their butter when margarine became available. They asked their politicians to stop the ‘demon spread’ from ruining their livelihoods. From 1877, US states including New York, New Hampshire and Wisconsin passed a series of laws banning margarine from being dyed yellow to resemble butter – and in some areas margarine even had to be dyed bright pink before it could go on sale. This resulted in a huge network of yellow margarine smugglers, breaking the law to get the spread onto the breakfast table.

The state of Wisconsin only lifted the final ban on margarine in 1967, when senator Gordon Roseleip agreed to take a blind taste test to prove that butter was superior. To his humiliation, Roseleip repeatedly picked margarine as the better spread. Returning home in defeat, Roseleip told his family, and was shocked when they revealed why he couldn’t tell the difference: worried about his health, they had secretly been using illegal, bootlegged margarine for years!

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@royalsocietyofchemistry Have you ever wondered what the difference is between butter and margarine? #learnontiktok #food #chemistry ♬ Butter Fingers - Kent, Lone

Kit Chapman

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