Fining preliminary trials

The amount of bentonite needed for fining (about 0.5-3.0 g/1) is determined by preliminary trials. If too much is used, both the colour and the flavour of the product are impaired. 

Once the reaction has started, the ferric ferrocyanide should be eliminated rapidly by fining and filtration (or centrifugation). In a preliminary trial (Ribereau-Gayon et al, 1976), it was observed that 30 g/hl of ferrocyanide reacted in two hours, but when contact time was reduced to ten minutes, only 14 g/hl reacted. If, in practice, the same wine were treated with 30 g/hl and the ferric ferrocyanide eliminated immediately, some potassium ferrocyanide would remain in solution, with all of the risks that this entails. 

It is easy to nnderstand the advisability of carrying out preliminary trials with different doses of various fining agents before fnll-scale fining (Section 10.8.1). 

In fining, the tannin-protein reaction is not stoichiometric and flocculation of the proteins is incomplete. Both reagents (tannins and proteins) may be present at the same time in a clear solution. In the case of overfining, potential turbidity appears after the addition of either tannins or proteins. This emphasizes the importance (Section 10.6.1) of preliminary trials (Section 10.8.1) before fining, followed by analysis, to check not only the efficiency of clarification but also the extent to which the wine has been stabilized. 

The gas-film coefficients are only 6 to 8 percent as large as the liquid-film coefficient, but the slope of the equilibrium line makes the two resistances comparable in magnitude. Values ofyj are obtained by drawing fines of slope —k a(l — y)i//Cj,a from the operating line to the equilibrium line. This requires a preliminary estimate of (1 — y) , but the lines are nearly parallel, and the first trial is usually accurate enough. If (1 y)j is assumed to be about 0.82 at the bottom,... 

In view of these remarks, it is advisable to carry out a laboratory test before fining a particular wine to assess the behavior of various products, possibly at several different doses. It should, however, be taken into account that fining in small volumes does not always reproduce the conditions found in the full-scale process. The complexity of this operation explains why preliminary fining trials are relatively little used in normal cellar practice. 

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