The Science and Magic of… Curry

By Andy Connelly

bandar kyaa jaane adrak kaa swaad
‘What does a monkey know of the taste of ginger?’

-Traditional Hindi idiom

For centuries spices drove our actions and imaginations. Empires rose and fell striving to control the spice trade, great men shipwrecked their careers in search of spice, and sailors were so bewitched that they claimed to be able to smell the spice islands of Indonesia or Zanzibar from far out to sea. Over the last few centuries we seem to have tamed our lust for spice; pouring our desires into one of their greatest expressions, curry.

The privileged inhabitants of these Isles have eaten spiced food since pre-Roman times. However, curry did not exist until centuries later when the British arrived in India and fell in love with the paradise of spicy dishes. From these dishes the British curry evolved and from Hannah Glasse’s 1747 curry recipe to the first curry powder in 1780 and the first curry house in 1810 the popularity of curry continued to grow. Then, when rationing ended after the Second World War, Indian restaurants began to open all over Britain. Now there are ten thousand ‘Indian’ curry restaurants alone. We have truly taken this “spicy stew of meat, fish or vegetables usually served with rice or bread” to our hearts.

The word curry has come to represents a plethora of wonderful dishes that come from different countries, cultures, and cuisines; from Korma to Kaeng Som, Pasanda to Soto Ayam. In my own kitchen I have always struggled to create the mouth-watering aromas and flavours that others achieve. Frustrated by this, I set out to try and understand how curry works; how these wonderful flavours are extracted, developed, and transferred to our senses.


This recipe is a simple Indian style curry that can form a great start to lots of other recipes.

  •  1 medium onion (chopped)
  • Ghee or groundnut / sunflower oil
  • A thumb of fresh ginger
  • 3 cloves or garlic
  • 1/2 tsp Turmeric
  • 2 tsp ground cumin
  • 1 tsp ground coriander
  • 1/2 chilli powder
  • 1 tsp garam masala
  • Around 30ml Water
  • About 500g of vegetables or meat of your choice
  • 1/2 – 1 tin chopped tomatoes
  • Fresh chilli as preferred
  • Small bunch of fresh coriander
  • Garam masala to taste (about 1 teaspoon)
  • Salt (to taste)

Step 1 – Make the sauce

 Blend together garlic and ginger with a little oil using a blender, or a pestle and mortar, to form a smooth paste. Take a frying pan, add a good quantity of ghee or oil and place over a medium heat. Add the onions and fry until they are translucent and soft; for more robust onion flavour fry until golden (but not burnt). Now add the garlic and ginger paste, cook for a couple of minutes and then stir in the spices with just enough water to form a thick paste; add a little more water whenever the paste drys out. Cook until the colour has darkened, this should take around 10 minutes.

Spices are nature’s chemical warfare; plants developed them as an unpleasant and often toxic, defence mechanism against bacteria, fungi, insects and mammals. While we are mammals we have developed methods of processing and extraction to turn their defence into our advantage. We find wonderful flavours in some of the most unlikely of places.

Recipes often recommend starting by dry roasting whole spices and then grinding them. Dry roasting mellows the spices by removing some of the highly volatile raw-tasting flavour compounds while developing new roast-like flavours and adding complexity. For example coriander seed becomes less floral and lemony, taking on a more grassy and earthy aroma. These changes come from the breakdown and recombination of flavour molecules and high temperature flavour creating Maillard reactions between amino acids and sugar.

To save time, here we use garam masala to achieve these roasted flavours. Garam masala is a blend of spices from India that have been pre-roasted and ground. Using pre-ground spices is not ideal as they lose much more of their flavour compounds over time compared to whole spices. Keeping pre-ground spices in a cold dark place, or better still grinding them fresh, will ensure that stronger flavours end up in your dish.

Another method of extracting flavours from spices is to cook them in fat. This allows the aroma compounds from different spices to interact and blend with each other. The fat then acts as a flavour sponge to hold flavour in the curry. As with dry roasting high temperatures can also generate new flavours, for example cumin develops a liquorice flavour. However, these high temperatures mean that these is a greater risk of burning the spices, especially ground ones. For this reason I add a little water to keep the temperature low and so help stop the spices from burning. You need to be careful not to add too much water as you may end up losing flavour compounds in the steam created from the water.

Alternatively, some recipes add the spices once the liquid base for the curry, such as tomatoes, has been added. Personally, I find this gives the curry a less aromatic, uncooked, flavour profile.

 Step 2 – Brown meat or vegetables

 Increase the heat and add the meat and / or vegetables to the spicy mixture. Stir and cook for around 2 minutes to get a good coating of sauce all over the meat and vegetable pieces and to ensure the meat or vegetables are well browned. To avoid overcooked vegetables you can cook them separately then add them to a pre-cooked curry sauce at a later stage.

Frying the meat and vegetables like this will create lovely roasted flavours on the surface as the sugars in the sauce react with the meat and vegetable proteins in a set of reactions called Maillard reactions. This browning reaction will not seal the meat juices inside but it will create flavour which will then diffuse into the sauce. Be careful not to add to much meat all at once as this will produce lots of liquid and you will struggle to generate the high temperatures desired for browning.

Fat is a key ingredient in curry. It provides a fantastic high temperature cooking medium, it acts as a flavour reserve, and it helps transfer flavour to the mouth. As most flavour compounds are more soluble in fat than water, flavour molecules held in water tend to be released very quickly in the mouth and so give a brief and intense flavour hit. In contrast, flavour molecules held in fat are released more slowly into the mouth, giving a less intense flavour but one that lasts longer and is generally more pleasant. Fat also coats the mouth, allowing flavour compounds to remain in the mouth longer and release flavour over an even longer period. It is for this reason that vegetarian curries, lacking fatty meat juices, often have extra fat added such as deliciously fatty coconut milk. My personal favourite is ghee because I love the rich taste.

One time-sapping aspect of many curry recipes is the overnight marinade. This is a step I tend to miss out as long slow cooking of your meat in a hot flavoursome stew will allow colour and flavours to penetrate much deeper, and tenderise the meat much more, than most cold marinades will.

Step 3 – Add chillies and base

 Add any chillies and further flavourings or ingredients to your taste and briefly fry them off. The ingredients you add here can further tune the flavours of your curry, guiding it North or South, East or West depending on your preferred flavours.

The Ayurvedic tradition specifies that six key elements of food should be included and balanced: sweet, sour, salty, bitter, astringent, and pungent. As an example, a Pathia-style curry uses tamarind (or vinegar) to achieve sourness and sugar for sweetness. Chillies on the other hand offer the pungent element, for example in a Jalfrezi-style curry.

The chilli, now a staple of many curries, was only introduced to India in the 16th century by the Portuguese. Before this peppercorns and relatives were used to add heat to dishes. The capsaicin molecules in chillies make certain mammalian nerve endings think that they are on fire. Luckily capsaicin, like many flavour molecules, is fat soluble, so a pint of fatty milk or lassi will help quell that fire more effectively than a pint of lager. In the same way, adding yoghurt, cream or coconut cream to a curry will bind the capsaicin and so helps cool an over spiced curry.

After adding these ingredients it’s time for the base for your curry, be it tomatoes, stock, lentils, or coconut milk. Careful not to make it too wet as you will dilute the flavours. If you want to make a dry curry you should add small amounts of base liquid into the pan bit by bit until the meat is tender. This slow dry cooking process creates deep, strong flavours and is generally how Bhuna-style curries are produced.

Step 4 – Cooking the curry

 The final cooking process can be done on the hob or ideally in the oven. Cooking in the oven at around 170oC has the advantage of keeping the temperature of the curry low (around 80oC) so that collagen in the meat is allowed to melt but the meat doesn’t toughen as can happen at higher temperatures. One of the ultimate slow-cooked dishes is the Rogan Josh. Originating from Persia, it is a fragrant dish with cardamom, fennel and other aromatic spices and is traditionally cooked in an oven. This long gentle cooking allows more time for flavours to mingle and create a rich, tasty sauce.

One problem with long cooking is the potential for flavours to escape; however, this can be minimised by keeping the lid on your dish. The stronger the smell of “spiced indian air” during cooking, the less flavour you will find in your curry! For this reason, if you find there is too much liquid diluting your curry, don’t take the lid off to evaporate the water. Instead, try adding a starchy ingredient such as finely grated potato, red lentils, or squash – this last option adds extra lovely sweetness. Other thickeners provide dry matter which will help thicken the sauce, for example tomato purée, ground almonds, or coconut cream.

Step 5 – Balance your flavours

 After your curry has been cooking for a lovely long time (minimum an hour for meat or until the vegetables are tender) it is time to taste it and see how the flavour molecules you added have changed along the way. Some will have been transformed through reaction with oxygen and other food molecules, really bringing the curry together. However, some will have been lost through evaporation which might leave your dish a little less exciting than planned.

To add any lost flavours back in we start with garam masala, which can provide a lovely fragrance to your curry when added near the end. Raw spices would not achieve this as they often also contain unpleasant flavours which need cooking off. A word of caution though; garam masala can be translated as ‘intense spices’, so be careful how much you add.

Another important addition to your spicy stew is salt. Salt reduces perception of bitterness in food and seems to enhance flavour perception. Finally, you can add lemon juice for extra zing and coriander leaves for a touch of lightness. These add flavour compounds that would not have survived the long cooking process and so freshen up the curry. But don’t be scared to experiment with other herbs; traditional Baltis from a region of northern Pakistan (not Birmingham!) are aromatic dishes loaded with various fragrant fresh herbs including coriander and mint.

Step 6 – Eat!

Prepare your favourite accompaniments, be it wheat flour-based breads, lentil flour-based poppadoms, or the endosperm of the rice plant. I am completely behind the sentiment reportedly expressed by the last Shah of Persia: “Eating with a knife and fork was like making love through an interpreter”. All I need is a large garlicky naan and my fingers. Alternatively, you could follow the example of some Indian soldiers as observed by a French jeweller, Tavernier. They made their meal more luxurious by dipping their fingers into a bowl of melted ghee as they ate. How’s that for flavour transfer?

Further reading

Image provided by qasic (


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