Heat Stability in White Wine


If an unstabilized wine has an excess of protein, this protein can come out of its solubilized form, flocculate and deposit at the bottom of the bottle. Usually this happens fairly quickly when an unstable wine becomes sits at a warm temperature for a couple of days. It can also happen at cellar temps, but usually takes a longer period of time to develop because cooler temps delay the flocculation reaction. Either way the result is that a  wine that was clear going into the bottle now contains fluffy, white clumps that swirl back up into the wine each time the bottle is moved, just like a snow-globe. Depending on how extreme the reaction is, the effect on the wine’s taste can be negligible to definitely detectible – though usually not  enough to ruin the wine. However the visual impact is always pronounced and negative. 

As we’ve seen, protein is removed by bentonite. Protein has a positive charge, and bentonite clay has a negative charge. When exposed to each other the two opposites attract and stick to each other like a pair of magnets. Clear wine will go cloudy when bentonite is added as the charged reaction pulls the protein out of solution. The protein/clay reaction product will then settle out at the bottom of the vessel, forming a deposit that the  clear wine will need to be racked off of. By weight, sodium-based bentonite is more reactive than calcium-based bentonite but creates very fluffy lees so we have a higher wine loss post-treatment. Calcium-based bentonite lees are more compact so we get a lower wine loss when we rack off post-fining, but calcium-based bentonites can be less effective so you often use more of the product to get the job done.  
Helpful Hint: The deposit for either type of bentonite can be condensed by the use of a small amount of gelatin, such as “Ichtyocolle” (FIN74) which also helps to clear the wine out.
Bentonite is a powerful tool.  If you use too much of it your wine will indeed be stable, but you will strip out flavours and aromas at the same time!   Determining the least amount needed to achieve stability is critical when planning to make your wine heat stable. The amount of bentonite needed to stabilize a white wine depends on the type of grape, vineyard location, growing practices, and vintage. In addition, the way the fruit is handled during pressing and crushing also has an effect on the final protein content of the wine (more movement/exposure time on skins = more protein). In short, each wine will have to be tested individually because there is no other way to know. This is done by doing a stability test (see below). 

Different bentonites will have a differing effectiveness as well as their own organoleptic impact on the treated wine. Each bentonite has a different molecular make-up, and each wine has a series of different proteins in varying ratios that make up the instability. This means that one type of bentonite may need a dosage rate of 4 g/gal to achieve stability, whereas another type of bentonite may need only 1 g/gal. As previously stated, using the least amount needed to achieve stability is important to avoid altering the original wine’s desirable characters too much. So bench trials are best done in 2 parts: 1) which product is best at preserving desirable qualities of your wine, then 2) how much of this one is needed to make the wine stable. Or just use the most effective one and call it a day.

All fining, by nature, alters the wine. A good way to think about this is to use an analogy of a house of cards. As the wine ages its various elements become increasingly interconnected through polymerization and a balance is struck in the overall equilibrium of the parts. The longer we go the higher we build. However, when we remove one of these pieces by fining (for example: to remove a protein that could potentially cause a haze in the bottle) we cause a shift in the structural balance of the wine and the wine will have to put itself back together again. Depending on how much of the compound that was removed, this can be a slight shift or the wine can change dramatically.  
The best time to fine for the purpose of removing a large portion of proteins is in the juice phase. Since this is before the wine has started to put itself together, removing protein at this stage does not create a loss of aromatic quality. Later when it is time to heat stabilize the wine, since we already removed some of the protein during the juice preparation, the amount of protein which remains to be removed will be reduced. This means that less bentonite will be needed and the wine will be less altered by the heat stabilization process.

Additionally, ageing on lees can build stability into the wine such that up to 50% less bentonite is needed.

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