Managing TSS / Acid Ratio

The TSS/Acid ratio is a key characteristic determining the taste, texture and feel of fruit segments. It is the sugar/acid ratio which contributes towards giving many fruits their characteristic flavor. It is also an indicator of commercial and sensory ripeness.

At the beginning of the ripening process the sugar/acid ratio is low, because of low sugar content and high fruit acid content, this makes the fruit taste sour. During the ripening process the fruit acids are degraded, the sugar content increases and the sugar/acid ratio achieves a higher value.

In the USA, a minimum TSS/acid maturity ratio of between 7 to 9:1 is typically desired for oranges and mandarins. For grapefruit between 5 to 7:1 is the standard for marketable produce.

In tropical climates harvesting of oranges commences when the minimum TSS/acid ratios are reached and the fruit has a green-yellow color on no more than 25% of its surface.

In Mediterranean climates, fruit is harvested when the appropriate TSS/acid ratio is reached and the fruit is orange on its entire surface. Exceptions in fruit color may be made in early fruit harvests; this fruit may be 'degreened' in ethylene chambers.

The TSS/acids ratio is determined by simple division. For example: if the oBrix value is 12 and the total acid value is 1.0%, the ratio would be 12. If juice had a oBrix value of 12 and an acid value of 0.8%, the ratio would be 15.

Crop Nutrition and Citrus TSS/Acid Ratio

The TSS/Acid ratio is reduced by high rates of nitrogen and potassium, and to a lesser extent, magnesium.

Nitrogen

Together with a slight effect on TSS content, high nitrogen rates will reduce the TSS/acid ratio. It is important not to use excessive N or harvest will be delayed.

Potassium

Potassium increases the content of organic acids in fruit juice. This increase in acidity may also reduce the TSS/Acid ratio. Thus, the correct K regime is important and will differ for the production of sweet oranges, mandarins, or acid lemons.

Boron, copper and iron

Boron, copper and iron may cause an increase in the TSS/Acid ratio. These trials illustrate the importance of copper in fruit quality and maturity.

Related articles

orange

Managing Citrus Total Soluble Solids (TSS)

The TSS content of the fruit is usually obtained from assessing the degrees Brix of the fruit. It is important that the grower aims to produce an acceptable balance of TSS and fruit acidity (see TSS/Acid ratio).
orange

Managing Citrus Fruit Acidity

During the ripening process fruit acids are degraded, the sugar content increases and the sugar/acid ratio reaches a higher value. Crop nutrition can influence citrus fruit acidity.
orange

Increasing Citrus Absorbic Acid Content (Vitamin C)

Vitamin C helps the body maintain healthy tissues and strong immune system and a cup of orange juice can contain almost 100mg of the vitamin. A balanced crop nutrition can help growing fruit with higher ascorbic acid (Vitamin C) content.
Role of Potassium in Citrus Production

Role of Potassium in Citrus Production

Alongside nitrogen, potassium is one of the most important nutrients for citrus production. It is needed for enzyme activation, cell division, photosynthesis, photosynthate transport and osmoregulation.
Role of Copper in Citrus Production

Role of Copper in Citrus Production

Copper in citrus affects photosynthesis, plant protein production, pollen viability and therefore fruit set, respiration and water use efficiency.

See all articles about citrus crop nutrition