(10 lb/1,000 gal). Above this addition level, a wine/ water mix can be used for rehydration to keep the processing water addition below 1 percent of total wine volume. Alternatively, rehydrating with too little water will limit the amount of swelling and makes for a difficult-to-stir, lumpy slurry.
Does a change in pH due to acidification/deacidification or cold stabilization change the protein stability of my wine?
Yes. Even small changes in pH can significantly alter the protein solubility and thus the wine’s bentonite requirements. Protein stability must be reassessed after any treatment that changes the acidity of the wine in question. Especially high pH values likely will lead to increased bentonite demand. Calcium bentonites are not recommended for wines with a pH above 3.4.
Can blending two protein-stable wines compromise the stability of the blend?
Yes. Any shift in alcohol content, pH, protective colloid concentration, etc. can potentially render the entire blend unstable. A new test of the mixture must be conducted, and additional fining might be needed.
Can nongrape proteins from fining agents, enzymes or lysozyme treatments, or sur lie aging influence the protein stability of my wine?
Gelatin and other proteins that are used as fining agents against over-extracted seed or skin tannins may contribute to protein instabilities and are often used in conjunction with other fining agents
such a silica gel (Kieselsol) — that can precipitate any excess fining proteins that didn’t bind to the wine’s tannins.
Additions of processing enzymes such as pectinases or glucosidases are usually not relevant sources for protein instabilities. However, they respond well to bentonite fining, which allows the winemaker, e.g., to stop the activity of β-glucosidases. This limits the premature release of sugar-bound varietal aroma precursors such as monoterpenes and a loss of aging potential for the wine.
Lysozyme additions to inhibit malolactic fermentation can add substantial amounts of nongrape-derived protein to the wine when
added at a recommended 250 to 500 mg/L, which is between 2 and 50 times the average concentration of natural grape protein in wine. Note that lysozyme
while potentially unstable — does not respond well to the heat tests.
Mannoproteins on the other hand, released from yeast cells during aging on the lees or added as commercially available adjuncts, may act as protective colloids and keep unstable grape protein from precipitating.
How fast/long should I mix?
The reaction between protein and bentonite is quick but not instantaneous. Proper mixing is crucial, and it has been shown that mixing speed, time, and temperature affect the efficacy of the treatment. At least 10 to 15 minutes of vigorous mixing is recommended, and the wine temperature should be above 50°F (10°C). To increase the effectiveness of the bentonite fining, the winemaker may choose to do it at a warmer temperature, and then proceed with a cold stabilization against tartrate precipitation thereafter. In this scenario, the dropout of potassium bitartrate may affect the pH of the wine, and the bench test for protein stability should address this by simulating the chilling beforehand.
It is important that any bench trial conditions, especially the mixing speed and the temperature, are representative of the conditions that can be achieved on a large scale in the cellar. Otherwise, an underestimation of the bentonite requirements will result.
Mixing with an inert gas fed in via the racking valve avoids potential oxidative damage due to mechanical mixing if the tank headspace contains traces of air/ oxygen.
How long does it take to settle?
Allow one week (depending on tank height) to have all bentonite lees settle to the bottom by gravity alone. Limiting the contact time between wine and bentonite helps to minimize the amount of lead residues that could be extracted into the wine.
Fining with Bentonite