When making fried yellow plantains, you need to choose the right ones, which will be yellow color and have very dark/black spots on them (like the picture below). The black spots are the perfect indicator that the plantains are ripe enough and perfect for this recipe.
The perfect yellow plantain is also firm to the touch but no completely. It should feel ripe with a certain resistance. You don’t want a plantain that is too ripe (with the peel mostly black) because it will be difficult to slice, it won’t hold its shape when cooking, it will absorb a lot of oil and it will be mushy. If you have yellow plantains that are overly ripe, they won’t be good for this recipe but you can use them to make Vegan Banana Bread (using yellow plantains instead!)
When you go to certain supermarkets, you sometimes see yellow plantain with a perfect bright yellow peel. If you buy those, wait for a few days until it ripens a bit more and you can see black spots. If you cook them right away, the fried yellow plantains won’t have the soft interior and caramelized flavor that is so characteristic.