Thai Peppers and the 50 Local Chili Lines Thailand Grows

What are Thai peppers?

Small, upright, hot chilies, grown on a scale you might not expect. In 2006/2007 Thailand planted 75,955 ha of chili and harvested 333,672 t, about 8.1 t per hectare, and over 60 % of that land grew small, erect-fruited chili, the prik khee noo¹.

Thai chilies are Thai by long use, not by origin. Like every pepper they trace back to the Americas, and the peppers by country page shows how they got to Asia. What you buy as a Thai chili in a shop abroad is one slice of a much wider crop, and the rest of this page shows you the other slices.

Which chilies do Thai farmers grow?

You'll find prik khee noo on the plains and local landraces in the hills. The table brings together what a Kasetsart University study and a Department of Agriculture survey say about each type¹².

With most of the chili land in one type, the small upright prik khee noo is the Thai chili most people mean. The hill lines are a different story: for the Karen chili, the Department of Agriculture notes a distinctive aroma and a hot bite².

If you buy seed, you'll meet both kinds, because Thai farmers keep both in use. The Kasetsart study puts the split at about 20 % F1 hybrids to 80 % open-pollinated varieties, and the 28 prik khee noo lines it tested came mostly from the Northeast, with a narrow genetic spread between them¹.

How hot are Thai peppers?

The Thai pepper sold in the United States rates 50,000 to 100,000 SHU, the top of the hot band⁵. That's 10 to 20 times an average jalapeño at about 5,000 SHU⁴.

On the chart you'll see the Thai chili sit above cayenne at 25,000–50,000 SHU and below the habanero at 100,000–350,000⁴. So if your recipe asks for five Thai chilies and you only have cayenne pods, expect a milder dish at the same count.

Local lines give you a much wider spread. Thailand's Department of Agriculture measured capsaicin in 50 lines and found anything from 14.12 to 2,111.61 mg per kg of fruit, with 36 of the 50 above 500 mg per kg². The UC Master Gardeners describe Thai chilies as fruity, sometimes citrusy and very spicy with lingering heat⁶, and that last word is the one to plan around.

A Kasetsart lab study of ten Thai cultivars gives you the field picture in Scoville terms: all but one rated 45,000 to 80,000 SHU, and two, Huarua and K07, went above 80,000³.

Are Thai peppers C. annuum or C. frutescens?

Both, and that's why sources disagree. The Kasetsart study says C. annuum and C. frutescens are Thailand's main cultivated species, and that the commercial hybrids are C. annuum¹. The Department of Agriculture's survey sorted 50 local lines by flower and seed color, and C. frutescens came out ahead, 33 lines to 16, with one line of C. pubescens, the rocoto's species².

So when UF/IFAS files the Thai pepper under C. annuum⁴ and the University of Guam lists Thai under C. frutescens⁷, both can be describing real Thai chilies. The Capsicum species key shows you how to tell which one is on your plant.

When and where do Thai chilies grow?

Prik khee noo grows mostly in the Northeast, then the North and the East¹. The Karen chili is a hill crop: farmers in Mae Hong Son grew 8,436 rai of chili in 2012, mostly local lines saved from year to year, often planted among upland rice or maize².

The highland year runs as a loop, because the seed for next season comes off this season's plants.

The survey found the Karen chili growing at up to about 1,000 m above sea level². If you grow Thai chilies in a pot far from Thailand, the useful lesson is the length of that season: from the May planting to the December pick runs about eight months, so your plants need a long warm stretch to give you their full crop.

How do Thai cooks use their chilies?

Fresh and processed. The Department of Agriculture's report names six uses, from fresh seasoning to curry paste and food color, and the use tiles above list each one².

Pounding them fresh in a mortar, drying them or taming a dish that came out too hot are all cooking with hot peppers questions, and that silo takes it from here. For curry paste and sauce, your choice of line matters more than the name on the bag, since the hottest Thai lines carry over a hundred times the capsaicin of the mildest².

Which Thai chili should you buy for your dish?

Start from how much heat your dish can carry, then pick by size. The three cases below come from the figures on this page.

• You want the familiar burn of a Thai restaurant dish: buy the small 1-inch Thai chili sold abroad at 50,000–100,000 SHU⁴, and if you're used to jalapeños, the Thai chili and jalapeño pair walks you through the jump.
• You want aroma as much as heat: look for the longer, 4–6 cm Karen chili, which the Department of Agriculture singles out for its smell².
• You're cooking for people who rarely eat chili: taste one pod first, since local lines differ in capsaicin by a factor of about 150².

Why does your dish come out hotter than last time?

Usually because the pods changed, not your recipe. Three causes show up in the sources: a different line in the bag (14.12 to 2,111.61 mg of capsaicin per kg across local lines)², a first-harvest batch, which runs hotter than later pickings³, and a different species behind the same "Thai chili" label¹. When you can, buy from the same seller each time, and add the chilies in two rounds so you can taste between them.