When buying apples (mainly red Fuji), it is best to choose ones that are red in appearance (called "striped red") and have some yellow inside. That kind of apple is crispy and juicy.

What is said on the third floor is also very correct, "Don't choose green ones with a little bit of red inside. They generally have a bland taste. Even if there is a lot of water, the sweetness must not be good. And the color cannot be special. Red, preferably somewhat pink but not completely red, with many red threads. In addition, the fruit base should be deeply sunken, so that the skin will be sweet and crispy with your fingers. They are sweet and crisp apples (the end without the handle is the pedicle, remember to choose the one with the deep pedicle for the best taste)."

In addition, the original poster can refer to the pictures.