Section IV. Remedial Actions

Transcription

1 Section IV Remedial Actions Occasionally, laboratory personnel must evaluate wines containing sediment and haze that are not biological in origin. Based on its visual appearance, Quinsland (1978) categorizes such sediment into three classes: crystalline, fibrous, and/or amorphous. The following paragraphs will acquaint the laboratory analyst with several rapid screening procedures that may serve as a basis for the more exhaustive testing that should follow. PRELIMINARY SAMPLE PREPARATION Generally, it is recommended that sediment and/or haze be concentrated somewhat prior to identification. In the case of sediment, this may be accomplished by pipetting or decanting the wine off the sediment and collecting the latter in a convenient container. With haze, however, it may be necessary to centrifuge the sample for 5 to 10 minutes or membrane filter the sample in order to concentrate the suspension. Once it has been concentrated, Tanner and Vetsch (1956) recommend washing the collected sediment in 5 ml of 95 % alcohol. This is most conveniently done by resuspending the collected sediment in the alcohol and recentrifuging. CRYSTALLINE DEPOSITS Potassium bitartrate and calcium tartrate instabilities are discussed in Chapters 13 and 18. For details regarding the formation of bitartrate/tartrate precipitates as well as their analytical determination, the reader is referred to these chapters. Additionally, filter acid (diatomaceous earth) may occasionally be seen (see photomicrograph IV-5), p Bright field microscope and several slides and cover slips Membrane filters and appropriate housing. Most laboratory filtration units utilize 47-mm membranes. For general purposes, 1-5-Jtm cellulose acetate filters are useful. Clinical centrifuge Magnesium oxide rods Cobalt filter 347

2 348 IV I REMEDIAL ACTIONS H 2S0 4 (1 + 3) Sodium metavanadate solution (3 % ) III. Procedure 1. Using the filter apparatus and appropriate membrane, collect a portion of wine sample containing the suspect sediment. 2. Rinse sediment/crystals with a small volume of distilled water, and apply vacuum to remove water. 3. Transfer the membrane to a watch glass. Place a drop of dilute sulfuric acid on the precipitate. 4. Add a drop of metavanadate solution. IV. Interpretation 1. Tartrate present in sediment turns yellow-orange in color. V. Alternative Test for Potassium I. "Load" a magnesium oxide (' 'magnesia") rod with sediment using the following technique: a. Using the flame from a Bunsen burner, heat the end of the rod and insert it into the collected sediment. b. Reheat the rod, and again insert it into the sediment. c. Repeat (a) and (b) if necessary. 2. When the sediment is concentrated into the magnesia rod, hold the loaded end in the outer portion of the flame. 3. Using a cobalt filter disk, the presence of potassium is indicated by a rose-color flame. VI. Microscopic Examination. l. See photomicrographs IV.I and IV.2. CRYSTAL-LIKE SEDIMENTS Cork dust appears "crystal-like" microscopically, and it may be confused with bitartrate unless further examination is performed. The recommended procedure is to use a stain that reacts with lignin, a structural macromolecule in cork. The equipment required is the same as presented in the preceding method. Phloroglucinol stain (made fresh daily) III. Procedure 1. Collect a portion of wine containing the debris by filtering it through an 8-pom membrane filter. (Membrane filters of 8 porn pore size may be ordered through supply houses carrying the Nucleopore product line.) 2. Wet the filter and sediment with phloroglucinol stain. Hold the stain in contact with sediment for 5 minutes.

3 Photomicrograph IV-1. Potassium bitartrate. * Photomicrograph IV-2. Calcium tartrate. *Photomicrographs IV-l-IV-5 courtesy of Ms. Wendy Single-Davidson, CSU, Fresno. 349

4 350 IV I REMEDIAL ACTIONS 3. Apply vacuum to the filter to remove the stain. Rinse the filter with distilled water. IV. Interpretation 1. Examine the sediment microscopically. Cork debris appears as red crystal-like aggregations of cells (see photomicrograph IV.3). 2. Case lint also stains red using this technique. However, it is fibrous in appearance (see photomicrograph IV.4). FIBROUS (CELLULOSIC) MATERIALS Fibrous materials found in finished wines usually are cellulosic in nature, originating from the filter pad matrix or from case lint that may get into bottles prior to filling. As above. Phloroglucinol stain Cellulose stain III. Procedure 1. Collect by membrane filtration a portion of the wine containing the sediment onto two separate membranes. 2. Stain the first membrane using the phloroglucinol technique presented Photomicrograph IV-3. Cork debris.

5 REMEDIAL ACTIONS 351 Photomicrograph IV-4. Cellulosic debris. above. Interpretation: Case lint (containing lignin) appears as red fibrous material. 3. Treat the second membrane with cellulose stain. a. Flood the filter and particulates with stain. Hold 5 minutes. b. Filter to remove the stain. Rinse with several milliliters of distilled water. Interpretation: Microscopically, cellulosic material not containing lignin appears light blue. (Note: Best results are obtained when the preparation is examined fresh. Color intensity diminishes after 30 minutes.) IV. Supplemental Note 1. Asbestos fibers are not stained using either of these techniques. AMORPHOUS MATERIALS Particulates with no defined shape, include protein and phenolics (and complexes of the two), as well as paraffin used to coat corks. Polycarbonate membrane filters (47 mm) and housing

6 352 IV I REMEDIAL ACTIONS Amido black 1O-B protein stain Eosin Y protein stain Folin Ciocalteu reagent H 2S % (wt/vol) K 4Fe(CN)6. 3H 2 0 III. Procedure for Protein 1. Filter sample containing sediment through an 8-Jlm poly carbonate membrane. Cellulose acetate membranes are unstable in the presence of protein stain. 2. Wet the membrane with stain, and hold 10 minutes. 3. Remove the stain by applying vacuum. Rinse with methanol-acetic acid solvent until the filter is white. Interpretation: Proteinaceous materials will stain blue-black microscopically. 4. With the above procedure, Eosin Y stain may be used instead of amido black 10-B. IV. Procedure for Phenolic Precipitates 1. Collect sediment by filtering sample through an 8-Jlm membrane filter. 2. Rinse with several milliliters distilled water and, with a spatula, transfer sediment onto a watch glass. 3. Using previously diluted Folin-Ciocalteu reagent, add a drop to sediment. Interpretation: Phenolic complexes dissolve to yield a slate gray to blue turbid solution. V. Alternative Procedure 1. Collect a portion of sediment in another test tube. Add 1 ml of concentrated H 2S0 4 to the sample, and gently heat it. Interpretation: a. Phenolics (pigments and tannins) present in the sample tum dark red. b. Carbonization is suggestive of protein. PECTIN INSTABILITIES 1. To a 25-mL aliquot of juice or wine containing unidentified haze, add 50 ml of 95 % ethanol or isopropanol. 2. The formation of a gel after several minutes is indicative of pectin. METAL INSTABILITIES On occasion, metal instabilities in the form of iron and/or copper complexes (casse) may be seen in bottled wines. Several screening tests have been proposed that provide insight into the nature of the instabilities (Tanner and Vetsch 1956; Amerine et al. 1980). Preliminary acidification of the suspect sample using 10% HCI is useful for

7 REMEDIAL ACTIONS 353 separation of metal-containing complexes from complexes of protein and phenolics. I. Procedure 1. Collect approximately 20 ml of the suspect wine. Add 3 to 5 ml of HCI ( 10% ), and note whether the haze dissipates or remains. If the haze solubilizes, proceed using the diagnostic scheme presented below. If the haze remains, the instability is probably due to protein or complexes of protein, protein-phenolics, or phenolics-phenolics (e.g., pigmenttannin). A method for the presumptive identification of proteins and phenolics is presented above. (a) Flame test for copper and organics 2. Collect 15 to 20 ml of the suspect wine. 3. Add 5 drops of H If the haze qissipates, Cu2+ is suspected. If the haze remains, see options below under (b). 5. If the haze can be concentrated by centrifugation or if sediment is present, collect a sufficient amount on a stainless steel laboratory spatula. Slowly dry the sediment over a Bunsen burner, and, when it is completely dry, attempt to ignite it by more intensive exposure to the flame. If the haze consists primarily of complexes of copper and organics, the sediment is partially burnt. However, copper sulfide and ferric phosphate casse will not bum. (b) Color formation tests for copper and iron 1. Collect 20 ml of the turbid wine in two test tubes. 2. To Tube 1 add several 5 ml of postassium ferrocyanide (0.5 %). Interpretation: Formation of red coloration is a positive presumptive test for copper and its complexes. 3. To Tube 2 add 5 ml of potassium ferrocyanide (0.5%) and 5 ml of HCI (10%). Interpretation: Formation of blue coloration is a positive presumptive test for iron. Photomicrograph IV-5. Diatomaceous earth.