Why Your Wine Isn’t Cloudy: The Proteins Behind a Clear Glass
Hold a glass of Chenin Blanc up to the light this festive season and it should be crystal clear. That’s not luck. It’s protein chemistry.
The Haze Problem
White and rosé wines naturally contain small amounts of protein from the grapes. The ones that cause trouble are mostly defence proteins, chiefly thaumatin-like proteins and chitinases, which the vine makes to protect itself against fungi. They are tough enough to survive fermentation and end up in the finished wine.
At first, nothing seems wrong. But if the bottle warms up, on a hot shop shelf, in a car boot or during a long shipment, these proteins can slowly unfold and clump together. The result is a haze or a fine sediment. It isn’t harmful, but to a customer, cloudy white wine looks faulty, and it can be sent back.
How Winemakers Prevent It
The standard fix is bentonite, a fine clay that binds proteins and settles to the bottom of the tank, taking them with it. Winemakers usually run a heat test on a sample first to judge how much bentonite a wine needs.
Bentonite works, but it is a blunt tool. It can strip out some aroma and flavour along with the proteins, and some wine is lost in the sediment. That is why researchers keep looking for gentler alternatives, and why using just enough bentonite, rather than a generous safety margin, is worth getting right.
Where Proteomics Comes In
LC-MS proteomics can identify which proteins are in a wine and measure how much of each is present. That mix changes with grape variety, ripeness, vintage and disease pressure, so two wines that look identical in the tank can behave very differently in the bottle.
Smarter fining: knowing which haze-forming proteins are present, and in what amounts, helps match the treatment to the wine instead of over-fining to be safe.
Testing alternatives: when a new fining agent or process is trialled, proteomics shows exactly which proteins it removes and which it leaves behind.
Allergen checks: some wines are fined with egg white or milk proteins. Mass spectrometry can check whether traces of these allergens remain, which matters for labelling and export.
Beyond clarity: proteins also influence foam in sparkling wine and mouthfeel in still wine, so the same tools help winemakers understand quality, not just fix faults.
A Western Cape Story
The Western Cape is one of the world’s great wine regions, and much of what is made here travels a long way to reach the glass. For an exporter, a wine that stays clear through a hot shipping container is not a nice-to-have. It is the difference between a product that sells and one that is returned.
So when you raise a clear glass this December, spare a thought for the proteins that aren’t there, and for the chemistry that took them out.
Trace Labs works with food and beverage companies on protein identification and quantification. If you produce wine or other beverages and want to understand the proteins in your product, get in touch.