The Science Behind A Curry

The Science Behind A Curry

Ever wondered why curry stains so badly or why cutting onions makes you cry?

The Science: [So what? So everything] campaign, which aims to highlight the science behind our everyday lives, has brought together some fascinating questions and answers about the science behind curry, including the potential health benefits of some of the ingredients that make up one of the nation’s favourite dishes.

For more information about the science behind curry and other areas of our everyday lives, visit

Why does chopping onions make me cry?

When an onion is sliced an enzyme in the vegetable is released and causes a chemical to split, creating a substance that is an irritant to your eyes and nose. You immediately start to sniffle and weep, and your tears continue until they’ve successfully removed the irritation.

Garlic contains a similar chemical, called alliin, but does not have the other reactive chemicals, so it does not make you cry when you slice it. Many tricks have been suggested to stop you crying when chopping an onion, including using a fan to stop the chemicals from reaching your eyes.

Is the crunch of poppadoms addictive?

There has been a lot of scientific research into the way your brain interprets the sound produced when you bite into something crisp and crunchy.

That cracking, snapping and popping sound, especially when you experience it at the start of a meal, could be telling you 'what I’m about to eat is fresh'.

Crunchiness also adds a completely different textural and auditory dimension to food which grabs your attention. This helps make poppadoms and bombay mix so more-ish.

Why does curry stain so badly?

Curry causes problematic stains due to the bright yellow molecule called curcumin which is found in turmeric. Turmeric can be used as a dye for clothes as its molecules bind very strongly to cotton and other fibres.

As well as causing clothes to stain, turmeric as an ingredient has also been found to have some health benefits.

Scientists recently found that curcumin - the chemical which gives this spice its yellow colour, is a great antioxidant source, and are exploring its potential to help liver and kidney function, and its possible connections with treatment of Alzheimer’s Disease. The research has a long way to go, but has shown some positive results in the lab.

Why is a chilli hot?

When you eat a chilli (or its powdered form cayenne pepper) the areas of your tongue that normally sense heat and pain are stimulated, telling the brain that the area affected is burning.

The substance responsible for this reaction is called capsaicin, which raises the heart rate, increases perspiration and the release of endorphins.

Contrary to popular belief, most of the heat in a chilli is found in the white pith, where the largest amount of capsaicin is found, rather than in the seeds.

The burning sensation caused by chillies leads to the release of endorphins, the body’s natural painkillers. These can give us a feeling of happiness, which is perhaps why eating a hot curry makes us feel good.

The heat of chillies is measured using a Scoville rating. The jalepeño pepper has a Scoville rating of up to 8,000, whereas the world’s hottest chilli pepper has a Scoville rating of over 1,000,000. Ouch!

Beyond its kick, capsaicin has potential for wide ranging pharmaceutical uses:

- It has been known to work for pain management in cases of muscle pain, headaches and cramping

- Some scientists have connected capsaicin with relief for nasal and lung congestions, helping to clear away mucus

- It has also been found to have notable cardiovascular effects such as reducing blood pressure, by dilating the blood vessels and increasing blood circulation. However it would take large amounts of cayenne pepper to see notable effects

Can the Indian side dish raita stop my mouth burning?

It’s possible that the yoghurt in raita might dissolve the chemical capsaicin (which gives chilli its heat) and reduce the heat experienced in your mouth’s pain sensors.

But raita might also help to reduce heat because it includes cucumber, the crunch of which provides the brain with enough distraction from the pain of the capsaicin to ease the feeling of discomfort.

Do other curry ingredients have health benefits?

As well as turmeric and chilli, popular curry ingredients, ginger and garlic, are also thought to have some health-kicks.


Ginger has many health benefits including relief for upset stomachs, anti-inflammatory and antioxidant effects.

Ginger is well known for soothing stomach and digestion problems. Ginger helps to neutralise stomach acids, and encourages the secretion of digestive juices.

Interestingly, research has shown that it can reduce nausea and vomiting in pregnancy, so it is not just at the end of the pregnancy that curry should be consumed!


Renowned for keeping our hearts healthy, garlic has been used medicinally for years. Garlic contains a chemical called alliin, which when broken down by our bodies, not only creates the pungent ‘garlic breath’, but also reacts with red blood cells and produces hydrogen sulphide which dialates the blood vessels.

In addition, garlic is an excellent source of selenium, which can help proper functioning of the immune system.

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