Inline dosing of bentonite
Background
Protein haze remains as one of the key potential instabilities in white wine production that requires costly treatment with bentonite. The majority of these costs are associated with the quality downgrading of wine recovered from the bentonite lees. Bentonite is prepared as slurry, added batch-wise to wine in a tank, and agitation is provided after which the bentonite is allowed to settle. Settling is slow and it can take up to a week before the wine may be racked off. Furthermore, the bentonite sediment or ‘lees’ occlude between 5 and 10 % of the volume of the treated wine. The occluded wine is normally recovered from the lees by rotary drum vacuum filtration. However, oxidation of the wine during this step leads to a significant downgrade in quality or ‘value loss’.
In-line dosing exploits the observation that protein adsorption by bentonite occurs rapidly – within several minutes. Furthermore, if combined with centrifugation, the bentonite and wine can be separated and the bentonite lees are simultaneously compacted to reduce value losses. In-line dosing methods for bentonite fining are already used by some wineries and anecdotal reports suggest that commercial applications are growing.
Progress
Results obtained from pilot-scale field studies of in-line dosing confirmed that a contact time of only a few minutes was sufficient for adsorption of the haze-forming proteins by bentonite. There was no detectable sensory impact on the wine of in-line dosing compared to batch addition.
These studies also observed a carry-over of bentonite from the centrifuge during in-line dosing of bentonite. This bentonite carry-over could be reduced by decreasing the operating flow rate to the centrifuge. Furthermore, Na-Ca bentonite was separated more easily by centrifugation than Na bentonites, and thus produced less carry-over at equivalent flow rates.
This carry-over problem, if centrifugation is used, is a disadvantage of the in-line dosing method because it contributes to downstream wine losses from tanks containing settled lees and/or constrains the throughput achievable. Some potential solutions that could be used to overcome this problem include: a more efficient centrifuge; multiple clarification steps; an alternative and more efficient clarification method; an alternative bentonite that is more easily clarified; and ‘counter-fining’ with another fining agent to improve bentonite separation
Highlights
- Pilot-scale field studies of in-line dosing were successful
- Only a few minutes contact time is required for adsorption of the haze-forming proteins by bentonite
Project team members:
Publications:
895 Colby, C.; Waters, L.; O’Brien, V. Fine tuning: cutting production costs of bentonite fining. Aust. N.Z. Grapegrower Winemaker (507): 51; 2006 (click here to order).
934 Colby, C.B.; Nordestgaard, S.; Waters, E.; O’Neill, B.K. Bentonite fining: can we improve performance and efficiency and decrease value losses? Aust. N.Z. Grapegrower Winemaker (509a): 82–88; 2006 (click here to order).
944 Muhlack, R.; Nordestgaard, S.; Waters, E.J.; O’Neill, B.K.; Lim, A.; Colby, C.B. In-line dosing for bentonite fining of wine or juice: Contact time, clarification, product recovery and sensory effects. Aust. J. Grape Wine Res. 12: 221–234; 2006 (click here to order).
1014 Nordestgaard, S.; Chuan, Y.P.; O’Neill, B.; Waters, E.; Deans, L.; Policki, P.; Colby, C. In-line dosing of white wine for bentonite fining with centrifugal clarification. Am. J. Enol. Vitic. 58(2), 283–285; 2007 (click here to order).