Filtration prior to bottling

Sweet wines, with potential for yeast refermentation, or wines with potential for malo-lactic fermentation, go through a membrane filtration prior to bottling. The membrane filters come in different porosities 0.65-p, pore size is used most commonly when 100 percent yeast removal is desired, and 0.45-p, pore size is used for malo-lactic bacteria removal. Proper sterilization of bottling equipment downstream of the membrane filter is essential to maintain the yeast- or bacteria-free nature of the wine after filtration. 

Analyses were carried out prior to bottling to verify that no contamination had occurred during the second filtration step. 

The sample should be sent as rapidly as possible to the laboratory, and when the analysis is not to be carried out immediately the bottles are stored horizontally and in a cool, but not excessively cold, place. Turbid samples are either left for some time and then decanted or filtered prior to analysis, the residue being examined separately if necessary. The determination of sulphur dioxide should be made before filtration and as soon as the bottle is opened. 

Zeolite Y gels were prepared by the same procedure outlined above. These gels were aged for 24 h at room temperature prior to crystallization. They were crystallized at 95°C for 64 h in polypropylene bottles without stirring (3). The products were separated by filtration, washed with copious amounts of water, and dried at 120°C. 

Losses of metals from dilute aqueous solution on storage are well documented. To prevent this it is usually necessary to acidify the sample after collection and filtration to pH 1. If the sample is to be analysed subsequently by flame AAS hydrochloric acid should be used (Section III.C.2) alternatively, prior to flameless electrothermal atomic absorption analysis, nitric acid should be added to preserve the sample (IV.B). The type of storage container is also important and high-density polyethylene is the preferred material for sample bottles. Here the adsorptive losses of metals appear to be lower than on glass. To avoid container contamination of the sample the container should be leached with dilute nitric acid for several days prior to use. This will remove surface contamination from the container material. Subsequent to the acid-leach, containers are washed in distilled-deionised water and then with a portion of the sample. Storage of samples for mercury analysis requires special conditions and these will be discussed later. 

Samples from the Suwannee River, Georgia, were collected from below the spillway draining the swamp during a 4-day period in early January 1994, which coincided with peak rainfall and high swamp water levels. Approximately 40 L of collapsed foam (approximately 150 L of aerated foam) were collected from quiet pools, allowed to collapse, and then combined into one container before returning to the laboratory for filtration and processing. A 100-L stream-water sample was collected in 4-L baked-glass bottles from the headwaters prior to departure from the site. 

For fractionation experiments, the perspex stirred cells (see Chapter 4 for equipment description) were operated directly from the nitrogen bottle without a reservoir. Membranes were floated in a beaker of MilliQ water, skin side down, for at least one hour to remove the glycerin coating. Then at least 300mL of MilliQ water were filtered through the membrane. The filtrate was analysed with UV and DOC to confirm full removal of glycerin. The membranes were reused up to 5 times and stored in 0.1 % sodium azide at 4 C. Pure water flux was measured after the filtration of 500 mM of MiUiQ water prior to each experiment. The filtration protocols for serial and parallel fractionation were described in Chapter 4. In this Chapter parallel fractionation results will be shown. 

The wine should be properly clarified prior to flat-sheet filtration at the time of bottling to ensure a satisfactory flow rate. This preliminary clarification may involve spontaneous settling, fining, centrifugation (Section 11.11) or filtration through a diatomaceous earth precoat (Section 11.6). 

It is vital to sterilize all equipment, and especially the filter and filter sheets, every morning prior to starting filtration and bottling. Table 11.9 shows the importance of sterilization. In particular, it is necessary in order to achieve perfect yeast retention, which is indispensable for sweet wines. If the system has not been sterilized, the first... 

When bottling line or other samples expected to have no or very low population densities are screened, it is necessary to concentrate known volumes by membrane filtration (<0.45 Xm) prior to microscopic examination. The volumes necessary under these conditions have been considered earlier (see Sampling Low Population Densities Sec 6.4.1 and 6.4.2). In this case, conveniently sized portions of the membrane may then be stained and examined directly. 

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