RESOLUTION OIV-OENO 662F-2023

SOLUBLE SOLIDS IN GRAPE JUICE, RECONSTITUTED GRAPE JUICE, CONCENTRATED GRAPE JUICE, AND GRAPE NECTAR

Type I method

THE GENERAL ASSEMBLY,

IN VIEW of Article 2, paragraph iv of the Agreement of 3 April 2001 establishing the International Organisation of Vine and Wine,

AT THE PROPOSAL of the "Methods of Analysis" Sub-Commission,

CONSIDERING that for grape juice, reconstituted grape juice, concentrated grape juice, and grape nectar is proposed the application of the Method OIV-MA-AS2-02 the Compendium of International Methods of Analysis of Wines and Musts,

DECIDES to add the following method:

SOLUBLE SOLIDS IN GRAPE JUICE, RECONSTITUTED GRAPE JUICE, CONCENTRATED GRAPE JUICE, AND GRAPE NECTAR

1.      Scope

This document describes the method used for determining soluble solids in grape juice, reconstituted grape juice, concentrated grape juice, and grape nectar, at the indicated concentrations ranging from 10.0 °Bx to 69.2 °Bx.

2.      Principle

The soluble solids content of a sample is estimated from its refractive index at 20 °C, expressed either as an absolute value or as a percentage by mass of saccharose (degrees Brix), the value is set out on the Table II to obtain the sugar content in grams per litre and in grams per kilogram for grape juice, reconstituted grape juice, concentrated grape juice or grape nectar.

3.      Apparatus

3.1.      Abbe refractometer

The refractometer used must be fitted with a scale giving:

• either percentage by mass of saccharose to 0.1 %;
• or refractive indices to four decimal places.

The refractometer must be equipped with a thermometer having a scale extending at least from + 15 °C to + 25 °C and with a system for circulating water that will enable measurements to be made at a temperature of 20 ± 5 °C. The operating instructions for this instrument must be strictly adhered to, particularly with regard to calibration and the light source.

Note:  An electronic refractometer can also be used. In this case, a correction is not necessary for devices that automatically take temperature into account.

3.2.      Analytical balance verified and calibrated with minimum precision of 0.01 g.

4.      Preparation of the sample

Pass the sample through a filter paper or dry gauze folded into four and, after discarding the first drops of the filtrate, carry out the determination on the filtered product.

In the case of concentrated grape juice, depending on its concentration, use the sample directly or prepare a dilution weighing 200 g of concentrated grape juice and adding purified water for laboratories (EN ISO 3696) up to 500 g (F = 2.5).

5.      Procedure

Bring the sample to a temperature close to 20 °C. Place a small test sample on the lower prism of the refractometer, taking care (because the prisms are pressed firmly against each other) that this test sample covers the glass surface uniformly. Carry out the measurement in accordance with the operating instructions of the instrument manufacturer used. Read the percentage by mass of sucrose to within one decimal place or read the refractive index to four decimal places. Carry out at least two determinations on the same prepared sample. Note the temperature in t °C.

6.      Calculation

6.1.      Temperature correction

• Instruments graduated in percentage by mass of sucrose: use Table I to obtain the temperature correction.

Table I - Correction to be made in the case where the percentage by mass of saccharose was   determined at a temperature different by 20°C.