Protein fining

Centrifugation is an important step in starch isolation that separates starch from fine fibers, insoluble or soluble protein, and gum or mucilage compounds. Centrifugation (usually 20 to 30 min at 5000 to 8000 x g, 20°C) settles the starch (a white layer) at the bottom of the centrifuge tube (Fig. E2.1.2). The water-insoluble contaminants (e.g., protein, fine fiber) form a dark or brown layer on top of the starch layer. This contaminant layer is normally removed manually by scraping with a spatula, being careful not to scrape away any of the starch layer. 

Wuthrich, K Protein structure determination in solution by nuclear magnetic resonance spectroscopy. Science 243 45-50, 1989. The most effective technique for determining protein fine structure in cases where x-ray diffraction cannot be used. 

Figure 65 The consumption by populations of different species coarse broken line, protein fine broken line, lipids broken and dotted line, total mineral matter solid line, glycogen.

Fining also may be done to juice prior to fermentation. Protein fining agents may be used to reduce phenolics in press juice, or bentonite used for protein reduction or reduction of potential for hydrogen sulfide (H2S) production (18). 

Zoecklein B.W. (1988a). Protein fining agents for wines and juices. Virginia Cooperative Extension, Publication No. 463-012. 

The hydroferrocyanic derivatives prodnced are in colloidal form. Their floccnlation in wine is accelerated by adding a protein fining agent. Fnr-thermore, precipitation of ferric ferrocyanide at least partially eliminates proteins (Vogt, 1931). This may be advantageous in white wines susceptible to protein turbidity. The precipitation of proteins is not due to the ferrocyanide itself, but rather to an insoluble ferric complex. Indeed, when potassium ferrocyanide is added to a wine containing no iron, no protein turbidity is observed. 

Several treatments are described elsewhere, in conjunction with the specific problems they treat or as applications of more general processes (physical treatments). This chapter presents clarification by sedimentation and racking, as well as protein fining and a few ofher freafmenfs not discussed in other sections. 

Every product used in protein fining has a specific action, according to its origin, and therefore its composition. 

Siliceous earths 20-50 ml/hl 50-100 ml/hl Act on protective colloids in wines that are difficult to clarify. Used with protein fining agents, prevents overfining and facilitates settling of the lees... 

Bentonite 20-50 g/hl Clarification of young wines. Eliminates colloidal coloring matter. Facilitates sedimentation of protein fining agents... 

In general, the effect of bentonite on red wines is comparable to that of protein fining. After flocculation and sedimentation, wines treated with doses of 25-40 g/hl of bentonite remain stable at low temperatures, staying brilliant and free of turbidity, even after several months. This treatment may be even more effective than gelatin (12 g/hl) or blood albumin (18 g/hl). It should, however, be taken into account that bentonite fixes anthocyanins, not only in discolored white wines but also in roses and young red wines. 

As bentonite flocculates in wine, with a behavior analogous to that of protein fining agents, experiments have been made in using it to clarify wine. In fact, its effectiveness in clarification depends on the type of bentonite and the composition of the wine. The only wines that may be properly clarified are reds or whites with low concentrations of polysaccharides and other protective colloids (Section 9.4.1), as these inhibit the flocculation and settling of the bentonite particles. In some winegrowing areas, bentonite is well suited to clarifying dry white wines, but elsewhere white wines may be more turbid after bentonite treatment than before. 

Siliceous earths associated with any protein fining agent produce the following effects ... 

Siliceous earths may be used with all types of fining agents. The best results, however, are obtained in combination with gelatins (liquid and cold soluble) and isinglass. These products are particularly suitable for clarifying wines treated with bentonite. Siliceous earths should always be used before protein fining agents but after other treatments (ferrocyanide, bentonite). 

Of conrse, fining conditions affect a wine s composition even more than filtration. Fining red wines with protein fining agents or bentonite rednces their color even more than filtration and is more likely to make them seem thinner. 

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