What is the difference between cayenne pepper, chilli powder, and paprika powder? They seem pretty similar. Are they interchangeable in recipes? Will it be a big difference if I substitute one for another?
Cayenne pepper powder comes from the cayenne pepper. It is hot/spicy, registering 30,000 to 50,000 Scoville units.
Chilli powder, depending where you live, can mean anything between pure powdered chilli pepper (location would determine the specific type of pepper) to a spice blend of chillies with cumin, oregano, and/or other spices. Depending on the brand (or if you make it yourself) the heat and flavor can vary.
Paprika is the dried and ground pepper capsicum annuum, the species of pepper that includes a wide variety of shapes and sizes, such as sweet bell pepper, jalapeno, New Mexico chili and cayenne. It appears that the tomato pepper is the most commonly used variety for the production of paprika. Of course, there are also smoked varieties (sweet, bittersweet, and hot).
I would say that they are generally not interchangeable. Just a little bit of cayenne, for example, will bring quite a bit of heat to your final dish. Chili powder will bring more flavor/spices than paprika.
It really depends on the final result you are looking for, but simple substitutions will result in very different outcomes.
They give a similar range of flavours, but in quite different proportions. They’re all made from ground roasted or dried red peppers of some kind, so all of them involve some amounts of spiciness (chilli heat), fruitiness, earthiness, and other aspects of the flavour of roasted peppers. Cayenne typically has much more of the hotter and sharper flavours among these. Paprika typically is much less hot, and more fruity and earthy (though there’s a wide range of varieties of paprika). A very wide range of different styles are sold as “chilli powder” depending where you are, but typically they’re quite hot and a bit earthy, less sweet than paprika and less sharp than cayenne.
(“Chilli powder” can also mean a spice blend from Mexican/US cooking, which besides pure chilli powder may typically contain cumin, dried onion/garlic, oregano, salt, and other herbs/spices. I’m assuming that you’re talking about pure chilli powder, not the blend.)
Since they have such closely related flavour profiles, you can usefully exchange them for each other in many recipes — it will change the result a bit, but will usually still work well. E.g. if a recipe calls for cayenne but if you or your guests don’t like too much chilli heat, you can subsitute paprika to reduce the heat without losing the other aspects of the pepper flavour.