What is fining and filtration in wine?
Quick answer
Fining and filtration are the one-two punch winemakers use to make wine clear and stable before bottling. Fining adds a substance — egg whites, bentonite clay, even pea protein — that binds to unwanted particles and drags them to the bottom. Filtration then passes the wine through progressively fine filters. Together, they prevent cloudiness and off-flavours — though some winemakers skip one or both on purpose.
Detailed answer
Think of fining and filtration as quality control for wine — and the heated debate around them as one of the wine world's most passionate arguments.
**Fining** works by chemistry. You add a substance that has an electrical charge opposite to the particles you want to remove. Positively charged proteins (egg whites, casein) attract negatively charged tannins and phenolics. Negatively charged bentonite clay grabs heat-unstable proteins. The pairs clump together, get heavy, and sink. You rack the clear wine off the top.
Different agents serve different purposes: egg whites (2-4 per barrel) are the classic choice for softening harsh tannins in red Bordeaux. Bentonite (30-80 g/hL) prevents protein haze in whites — essential for shelf stability. Fish-derived isinglass produces brilliant clarity in delicate whites. And for vegan wines, pea and potato protein alternatives now perform nearly as well.
**Filtration** is mechanical. The wine passes through increasingly fine barriers. Coarse filtration (diatomaceous earth) catches yeast cells. Plate filtration (1-5 µm) catches most remaining particles. Membrane filtration at 0.45 µm is effectively sterile — nothing alive gets through. Modern crossflow (tangential) filtration is gentler, pushing wine across the filter rather than through it.
The controversy: many natural and artisanal winemakers skip fining and filtration entirely, arguing they strip flavour, texture, and complexity. Studies show sterile membrane filtration can reduce polyphenols by 5-15%. The counterargument: an unfiltered wine with residual yeast or bacteria can develop off-flavours or even referment in bottle. It's a philosophical choice as much as a technical one.
As a consumer, look for 'non collé, non filtré' on French labels or 'unfiltered' on English ones. These wines may have sediment — it's harmless and often a sign of minimal intervention.
| Filtration type | Pore size | What it removes | Impact on wine |
|---|---|---|---|
| Diatomaceous earth | 5-20 µm | Yeast, coarse particles | Minimal flavour impact |
| Plate (cellulose) | 1-5 µm | Fine particles, some bacteria | Low impact |
| Membrane (sterile) | 0.45 µm | All microorganisms | Can reduce body and colour 5-15% |
| Crossflow (tangential) | 0.2-1 µm | Microorganisms, colloids | Gentler than membrane |
| No filtration | N/A | Nothing removed | Full texture, higher risk |