What methods exist for wine protein haze removal?
Wine haze derived from proteins is an aesthetic problem in white wines, and as such most winemakers choose to remove it.
Haze-forming proteins are highly stable during winemaking, but some will precipitate over time or with exposure to elevated temperatures.
If left untreated, wine haze formation is likely in wines stored at room temperature, or transported in warmer climates.
Haze formation depends on various factors:
- pH (higher pH -> lower stability)
- Alcohol content
- Grape variety
- Grape maturity at harvest
The process of wine protein haze formation is shown below.
Bentonite rock / Dinosaur Provincial Park, Alberta, Canada
Traditionally bentonite fining is used to remove both stable and unstable proteins. The goal is to use as little bentonite as possible while lowering the unstable protein content to a level at which precipitation will not occur in the bottle.
Bentonite is an absorbent clay, it was named by Wilbur C. Knight in 1898 after the Cretaceous Benton Shale near Rock River Wyoming.
- The type of bentonite (Sodium, Calcium, Potassium, Aluminium), the source, and its purity influence its properties.
- Sodium bentonite, more common in the Americas, Australia and NZ, typically has higher reactivity for enhanced adsorption.
- However calcium bentonite, while lower in reactivity, results in more compaction for lower generation of fining lees.
As well as absorbing wine haze components, bentonite may also indirectly adsorb some phenolic compounds via binding with wine proteins that have complexed with phenolics. Bentonite can also impact red wine color directly by binding with positively-charged anthocyanins.
How is bentonite currently prepared and used?
Bentonite fining is the current industry standard for wine protein stabilization to ensure that wine haze does not appear in the bottle.
- Bentonite is hydrated overnight prior to use.
- The bentonite is manually added to the wine tank and allowed to settle for days or even sometimes weeks prior to filtration.
- Although the reaction time is almost instantaneous, the settling time generally improves downstream filterability and is a requirement for some membrane filtration systems.
- Depending on the type of bentonite, the lees volume after treatment can range from 2 to 10% leading to high waste volumes or the necessity to implement further techniques to recover more wine.
Please see below for Pall’s innovative Oenofine XL Filtration System that allows effective and cost efficient removal of wine haze. Pall also offers the Oenoflow ™ HS Filtration System to recover valuable product from bentonite lees.