Key to good cider is buying apple trees with the right blend of acidity, tannins and sugars.
A mix of apples is required as few apples produce juice with such a mix. Thus, it is common to buy true cider apples with high levels of tannins as well as acidic apples to raise the acidity.
Tannins contribute to the mouthfeel and taste of a beverage, while acidic apples prevent against spoilage by microorganisms and add sharpness. Sugar drives the alcohol content.