RESOLUTION OENO 4/95

CATION-EXCHANGE RESINS

THE GENERAL ASSEMBLY,

IN VIEW of article 5, paragraph 4 of the International Convention for the Unification of Methods of Analysis and Appreciation of Wines of 13 October 1954,

ON THE PROPOSAL of the Sub-Commission of Methods of Analysis and Appreciation of Wines, DECIDES :

to supplement the International Oenological Codex with the monograph "Cation Exchange Resins for the Tartaric Stabilization of Wines ».

Definition:

Ion exchange is the reversible exchange of ions between a liquid and a solid during which the solid does not undergo any substantial change. In the application of this technology to wine, the solid is an insoluble porous synthetic resin which can exchange ions with the wine with which it is in contact.

Composition :

Cation exchange resins may be prepared in an appropriate physical form using one or several of the following formulae:

1. Sulphonated copolymer of styrene and of divinylbenzene.

2. Methacrylic acid-divinylbenzene copolymer.

The resin must be satisfactorily inert.

Substances which can be used in the manufacture of these resins are listed in annexes 1 and 2.

The resin should contain no more than 1 part per million of organic extracts obtained with each of the following solvents: (a) distilled water, (b) 15 percent alcohol, (c) 3 percent acetic acid.

The resin will have been washed and prepared according to the manufacturer's directions and subjected to the following test: using a separate ion exchange column for each solvent, prepare each column using 50 ml of the ion exchange resin which has been prepared according to the manufacturer's instructions. While maintaining the highest temperature which will be encountered during use, pass the three test solvents through these resins at the rate of 350-450 ml per hour, distilled water, 15% (by volume) ethyl alcohol, and 3 per cent (by weight) acetic acid. The first litre of effluent from each solvent is discarded, only the next two litres from each are used to determine the organic extracts.

The two litre sample is carefully evaporated to constant weight at 105°C; constituting the total extract. This residue is fired in a furnace at 850°C to obtain constant weight; constituting the ash. Total extracts minus ash equals organic extracts. If the organic extracts are greater than 1 part per million of the solvent used, a "blank" should be run on the solvent, and a correction should be made by subtracting the organic extracts found in the "blank" from the organic extracts obtained in the resin test. The solvents used are prepared as follows:

Control reagents:

Distilled and/or deionized water.

Ethyl alcohol at 15 per cent volume obtained from ethyl alcohol and distilled and/or deionized water.

Acetic acid at 3 percent volume made by mixing 3 parts by weight with 97 parts in weight of distilled and/or deionized water.

Limits:

1. Such a treatment must not alter the character of the wine.
2. The treatment must not reduce the colour of the wine.
3. The treatment must not reduce the metallic cation concentration in the wine to less than 300 mg/l.
4. Treatment must not lower the pH of the wine to less than 3.0. The reduction of the pH must not exceed 0.3 pH units.
5. The resin must not impart to the wine any material or characteristics (due to the resin treatment) which do not normally exist in wine.

The winemaker may employ conditioning and/or regenerating agents consisting of water and inorganic acids, provided the conditioned or regenerated resin is rinsed with water until the resin and container are completely free of unreacted (excess) conditioning or regenerating agents prior to the introduction of the wine.

1.      Annex 1

Substances utilisables dans la fabrication des résines échangeuses d’ions servant au conditionnement des denrées alimentaires.

Annexe 2

Substances provisoirement utilisables dans la fabrication des résines échangeuses d’ions.