Why are Gala apples sour and hard?

Because Gala apples contain polysaccharides, potassium ions, pectin, tartaric acid and other substances, which can neutralize acid radicals in acidic body fluids, they will taste sour.

Gala/Bila apple, also known as Jialiguo, is a kind of apple. It is a hybrid of orange apple and marshal. It is native to New Zealand and is characterized by bright fruit color, golden flesh, sweet and sour taste. Gala apple was planted in a large area in China after its introduction, and gradually became the main variety of early-maturing apples in China.

Early-maturing apple, 1962, named Discovery, was introduced from Holland by Fruit Research Institute of China Academy of Agricultural Sciences on 1979. The fruit is large, with an average single fruit weight of 140g, with regular size, oblate shape, yellow-green background, full bright red to dark red, good appearance, smooth luster, no rust spots and no edges.