Korean hot pepper flakes are vibrant and red. They are milder than other red chili flakes because there are no seeds. You cannot substitute anything for it.
It is best to buy the flakes labeled as “<em>coarse</em>” cut.
Although Korean cuisine offers an array of delicious “non-spicy” dishes, it is also renowned for dishes imbued with fiery spiciness. The spicy bite to many Korean dishes and recipes is invariably due to a single core ingredient: gochugaru (red chili flakes).
Gochugaru is made by drying Korean red chili peppers in the sun, removing the seeds and then crushing them into flakes.
Surprisingly, red chili pepper was adopted by NOT Koreans not too long ago (late 16th century), totally shifting the paradigm of Korean cuisine from that time forth. Today, gochugaru (Korean Hot Pepper Flakes or Korean Red Chili Flakes) is one of most essential ingredients in Korean cooking. It simply cannot be replaced with chili flakes or sauces from other places when it comes to cooking authentic Korean food. Korean hot pepper flakes are usually a vibrant red, coarse in texture and fairly spicy in taste, with a hint of sweetness. How they rate on the spiciness meter can vary depending on the region of origin and its specific farming conditions.