Heat Is a Spectrum, Not a Switch

Ask ten cooks from Sylhet how hot a curry should be and you will get ten different answers. Heat is not a single dial you turn up or down; it is a layered thing, built from the type of chilli, how it is prepared, when it goes into the pan and what you cook alongside it. The compound responsible, capsaicin, sits mainly in the pale pith that holds the seeds, not in the seeds themselves. It is fat-soluble, which is why a spoonful of yoghurt or ghee calms a mouthful far better than a glass of water. Once you understand that, adjusting a curry for your household becomes a practical skill rather than guesswork.

The Chillies You Will Actually Find in a British Kitchen

Scoville ratings are approximations at best, and the same variety can vary wildly depending on the season, the grower and how ripe it is. Use these as a rough map rather than gospel.

• Naga morich and bhut jolokia (roughly 800,000–1,000,000+ SHU): The pride of Sylhet, and genuinely fierce. A little goes a very long way. Half a chilli will heat a curry for four people generously.
• Scotch bonnet (100,000–350,000 SHU): Fruity and floral as well as hot, with a sweetness that works well in fish curries and achars.
• Bird's eye (50,000–100,000 SHU): Small, thin, reliable. The workhorse for those who want real heat without the naga's bitterness.
• Ordinary green finger chillies (5,000–50,000 SHU): The ones sold loose in most shops, and the least predictable. Taste a sliver before you commit — the same punnet can range from gentle to sharp.
• Dried red chillies (30,000–50,000 SHU): The backbone of baghar tempering. Their heat is rounder and more savoury than fresh.
• Kashmiri chillies (1,000–2,000 SHU): Barely hot at all, but they give that deep red colour without which many curries look washed out.
• Paprika and mild powder (0–1,000 SHU): Useful for colour and bulk when you are cooking for children or guests who prefer things gentle.

How Sylheti Cooking Builds Heat

In a Sylheti kitchen, heat rarely comes from one source. A typical fish curry might have slit green chillies dropped in late for aroma, a baghar of dried red chillies and panch phoron at the start for depth, and a spoon of achar at the table for anyone who wants more. Bhortas take a different route altogether — dried chillies are toasted and ground with mustard oil, which gives a smoky, almost nutty heat rather than a sharp one. Notice too that naga is often used sparingly and deliberately, in small amounts or in pickles, rather than dumped into every pot. That restraint is a technique, not a compromise.

Techniques That Change the Heat Without Changing the Chilli

The variety you buy matters, but how you handle it matters just as much.

• Leave chillies whole and slit if you want fragrance and a gentle background warmth. They release far less capsaicin than chopped ones.
• Scrape out the pith and seeds to cut heat dramatically while keeping the flavour. A teaspoon does this in seconds.
• Add chopped chilli early in hot oil for maximum heat, because the capsaicin dissolves into the fat and spreads through every bite.
• Add slit chillies in the last five minutes for a fresher, greener, milder result.
• Balance with fat, salt and acid — yoghurt, coconut milk, ghee, a squeeze of lime or tamarind, a pinch more salt. Sugar and jaggery help too, which is part of why a good achar tastes hot and sweet at once rather than simply brutal.

Be aware that long cooking does not destroy capsaicin. A curry simmered for two hours will still be hot, just better integrated.

Splitting the Pot for a Mixed Household

The most reliable trick in any family kitchen is to cook the base mild and add heat at the end. Simmer your curry to the point just before the chillies go in, then ladle out a portion for the children or the heat-shy, and only then finish the rest. If you have already gone too far, stir through a few spoons of plain yoghurt or a splash of single cream, and serve with a cooling raita or a bowl of plain rice rather than more bread. Keeping a jar of achar on the table lets everyone take their own heat into their own hands, which is exactly how it is done at home in Sylhet.

Build Your Own Heat Map

Taste every batch of chillies before you cook with them, keep a note of which shop or market stall gives you the ones you like, and label your frozen and dried supplies with the variety and rough heat. After a few months you will know instinctively that two of your usual green chillies equal one bird's eye, or that a quarter of a naga is perfect for a Sunday beef curry. That personal knowledge is worth more than any chart.