While reviewing my recipes today, it dawned on me that you may need to know a bit about aji amarillo–the key ingredient to most Peruvian dishes–before you can really dive into my recipes. Here’s a quick tutorial on what it is, what forms you can buy it in and where it is available.
There are several variaties of ají peppers grown in Peru, but ají amarillo is without a doubt the most commonly used. Long and slender with a vibrant orange color (not in fact yellow as the Spanish name would have you believe), the lingering heat and unique fruitiness of this pepper is impossible to replicate. Whenever using whole peppers in my recipes ,they have been seeded (like you would do with a jalapeno). If you would like to leave the seeds in, that’s fine. Just keep in mind that the peppers will be much hotter this way. My recipes are already on the hot side, so I would not recommend using the full amount when using unseeded peppers.
Aji amarillo peppers, as far as I know, are not available in their fresh form in the United States. Perhaps large cities with vibrant Peruvian communities will have them, but Madison certainly does not. Fortunately, I have used frozen, canned and paste forms, all of which worked beautifully. I found a bag of frozen Goya brand aji amarillo peppers in Madison at Yue-Wah Oriental Foods in Madison. This is what I used exclusively during my first month of cooking and they worked well. I just thawed a few as needed.
The jar pictured at the top of the page contains whole aji amarillo peppers in another form. Instead of being frozen, they are stored in a brine that preserves them. I was a bit skeptical to use peppers that were soaked in a brine for who knows how long, but I opened them up one day when I ran out of frozen peppers and diced them for a batch of salsa criolla. They behaved exactly like frozen varieties. This specific jar is also available at Yue-Wah in Madison. It is also available at Amazon.com along with other brands.
Instead of using whole aji amarillo peppers, you can also use pastes. A couple of my favorite brands are pictured above and below (click on them to take you to their product page on Amazon.com). Especially useful if you don’t live near a city with a thriving ethnic community, a variety of pastes are available online for reasonable prices. When using aji amarillo paste as a substitute for fresh diced aji amarillo peppers, remember that 1 tablespoon of the paste equates about 1 1/2 whole seeded peppers. Also, I recommend always using a bit less than the recipe calls for at first because every paste (both brand and batch) varies quite a bit in heat. Again, if you live in the Madison area, Goya brand aji amarillo paste is available at Yue-Wah for around $3.
One Country at a Time 
excellent post – clear and informative! Makes it not so intimidating to buy these.
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Nice job on the blog, keep up the good work. I’m a Peruvian in Madison and just so you know, Savory Accents often sells aji peppers (both aji amarillo and aji panca) at the farmers market, both as individual fresh peppers or as plants. The aji amarillo peppers I’ve seen usually look more like a greenish yellow, rather than the expected yellow/orange color, but it may be a question of ripeness. I’ve also found aji amarillo paste at La Hispana, a small Latin store on Fish Hatchery, as well as frozen aji peppers.