Managing Sugar/Acid Ratio in Apples

Apple flavor and taste are related to the level of soluble solids in the fruit, which are mainly sugars. Total Soluble Solids (TSS) is therefore of extreme importance to measure the quality of apple.

Referred to as oBrix, TSS is assessed by refractometry or near-infrared spectroscopy and can be used to check fruit maturity and ripeness, important to determine harvest timing. A balanced crop nutrition can influence TSS content of fruit.

Crop Nutrition and Apple TSS Content

Nitrogen and potassium

Nitrogen has a positive effect on the soluble solids content of apples. Potassium also plays an important role on sweetness, measured by oBrix, as shown in trials in India. °Brix is used to approximate the TSS content because the soluble sugars usually represent more than 75 - 85% of the soluble solids.


Apple acidity is a relevant characteristic for both fresh and processing markets. It is one of the main group compounds determining flavor. The higher the level of acidity, the more tart the flavor and the better the thirst-quenching properties of processed soft drinks. Magnesium has a slight effect on fruit acidity.