SOP: Determination of Brix:Acid Ratio

GIFSQ — Global Institute for Food Safety & Quality

Principle

The Brix:acid ratio is the ratio of °Brix to the grams of anhydrous citric acid in 100 g of citrus juice or concentrate. A higher ratio indicates a sweeter product and vice versa: a ratio of 14.0 means that for every 14.0 parts of soluble solids (mostly fruit sugars) the sample contains one part of acid.

Apparatus required

• As required for the determination of total soluble solids (Brix) and titratable acidity

Procedure

Determine the degrees Brix of the sample (by hydrometer or refractometer, as applicable)

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Determine the titratable acidity of the sample, expressed as per cent anhydrous citric acid

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Divide the degrees Brix by the percentage of titratable acidity; express the ratio to the nearest first decimal place

Calculation

Brix:acid ratio = °Brix / % titratable acidity (as anhydrous citric acid)

Worked example from the book: a juice with a Brix of 11.2° and an acidity of 0.8% gives a Brix:acid ratio of 11.2 / 0.8 = 14.0.

Precautions

• Both the Brix and the acidity must refer to the same sample — the ratio is meaningless if they come from different portions.
• Express the acidity as anhydrous citric acid before dividing, or the ratio is not comparable.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.