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Explainer Science

Wine Fining and Filtration Explained

A short guide to two key winemaking techniques

Meg Maker By November 12, 2021
illustration of person looking through different wine glasses
Illustration by Richard A. Chance

It’s morning in the restaurant kitchen. A prep chef stirs a slurry of egg white into cold chicken stock and slides the pot onto a slow burner. After simmering and straining, it will become crystal clear consommé.

Meanwhile, another chef grinds fresh tomatoes and sets the pulp aside to settle. Later, she’ll decant off the tomato water, then filter it for the somm’s seasonal martini.

These two processes — clarification and filtration — also take place in wineries. Like their kitchen analogs, they help winemakers create clear liquid. 

But unlike those cooking steps, wine clarification and filtration are curiously controversial. The argument spins around questions of authenticity, intervention, consumer expectation, and just plain flavor. 

Just what are these processes, anyway, and why should any wine lover care enough to argue about them?

Fining explained

Fining and filtration are used in making all styles of wine: still, sweet, and sparkling.

Fining is a centuries-old process to clarify wine. A winemaker stirs a small amount of a fining agent into a vat of wine, and this material attaches to microscopic particles held in suspension. The whole mass then precipitates out, an action called flocculation.

The process rids wine of proteins, long-chain tannins, pigments, unwanted microbes, and other materials that could later polymerize and turn the wine cloudy or cause it to reboot its fermentation in the bottle. Most white wines and many red wines are subjected to one or more fining steps. 

There are two main categories of fining agent: protein-based, called proteinaceous, and inorganic. While the proteinaceous substances historically came from animal products, substitutes are now available. Inorganic substances include clay, carbon, and synthetics. Winemakers choose an agent based on the specific ends they’re trying to achieve.

The following fining agents are used today:

  • Albumen, from eggs.
  • Casein, potassium caseinate, from milk.
  • Isinglass, isolated from the swim bladders of fish.
  • Gelatin, from animal byproducts.
  • Chitosan, formerly from shellfish but now exclusively from Aspergillus niger, a fungus.
  • Pea protein.
  • Bentonite clay, sodium bentonite, commonly sourced from Wyoming.
  • Kaolin clay.
  • Charcoal, activated carbon.
  • Silica.
  • Polyvinylpolypyrrolidone (PVPP), a binding agent, also used in aspirin.

Fining helps fix the color of white wines, although it can remove some color from reds. In removing tannins, it also helps smooth the wine’s texture; many winemakers who forgo all other manipulations do opt to use a fining agent to create that silkiness.

Because fining agents don’t remain in the wine, they’re considered processing aids, not strictly ingredients.

Filtration explained

Filtration, a technique introduced in the middle of the 20th century, is now widespread. It involves pumping the wine through thick cellulose pads or a synthetic membrane to screen out undesired particles and microbes. It’s a mechanical process.

Filtration may be done at various stages, for example, just after primary fermentation, prior to moving the wine into barrel, or right before bottling.

Thicker filter pads are generally used earlier in the winemaking cycle to remove large particles. This is called gross filtration.

Thinner membranes are used later to rid a wine of all remaining proteins, dead yeasts, bacteria, and other debris. The tightest membrane has a pore size of just 0.45 micrometers and produces an utterly sanitized product. This step is called sterile filtration.

Reverse osmosis is a form of membrane filtration that turbo-charges a winemaker’s toolkit. It essentially lets a producer disassemble wine into its constituent parts — water, alcohol, solids — then recombine it into the desired finished form: more dilute, more concentrated, more alcohol, less alcohol. Rinse and repeat.

Why some people love them

Winemakers embrace these techniques for several reasons.

  • First: flexibility. Producers might deploy them ad hoc to counter, or at least modulate, unwelcome surprises: an outbreak of Brettanomyces, a wine with too-harsh tannins, or one that wound up with too much residual sugar.
  • Second: cashflow. The approaches allow producers to swiftly clarify and stabilize their wine so they can bottle and ship it sooner. This lowers the cost of production and gives them an earlier payday.
  • Finally: efficiency. Big producers use these techniques to make wine for those consumers who value a consistent, low-cost product. Call them commodity wines, supermarket wines, or what you will, but that category makes up the overwhelming majority of wines sold in the U.S.

Why some people don’t

Some regard these tactics as shortcuts, suitable for bulk wine production but not for quality wines. That’s because fining to some degree, and filtration to a greater degree, can impoverish a wine by stripping delicate aromatics, robbing it of subtlety and finesse.

Filtration is regarded as especially rough handling because it alters the wine’s structure and consequently its feeling on the palate. The process can also introduce oxygen, which ages the wine prematurely and may generate other unwanted reactions.

Neither process is essential to produce a clear, clean, high-quality wine. Wine can be clarified by letting it settle and then gently moving it off its sediment. This step, called racking, involves decanting the wine from barrel to barrel via gravity. It may need to be repeated several times, and it can also introduce oxidative faults if mishandled. But essentially, a naturally clear wine is possible, it just takes a while.

Still, the heart of the debate isn’t chemical or mechanical, it’s philosophical: How much winemaking is enough, and how much is too much?

Many argue that less is more. They regard such tactics as unnecessary manipulations that silence a wine’s unique voice, or at least mute it. Natural winemakers almost universally avoid these techniques, although some still fine their wine according to tradition. But even some winemakers who don’t call themselves natural leave their wines unfined and unfiltered to preserve the nuances and quirks that add up to character. 

So, are fining and filtration useful tools that make wine more accessible, or needless interventions that strip wine of its vital force? There are myriad examples at both extremes, but there’s also middle ground, one that gives makers leeway to create a clear artisanal product. 

You may not like canned soup, but you might order a bowl of that consommé.

6 unfined and/or unfiltered wines to try:

bottle of La Valentina Spelt Montepulciano d’Abruzzo Riserva DOC 2017

La Valentina Spelt Montepulciano d’Abruzzo Riserva DOC 2017 ($18)

La Valentina’s Spelt Riserva ages 16 months in a mix of wood barrels and casks, and is bottled  filtered but not fined; the winery notes that it is suitable for vegans. Its robe is saturated raspberry red and the fragrance is cherry-scented with notes of cedar, juniper and tobacco. The tannins are supple, like corduroy. It’s a great wine for richer cuisines; try sausage flecked with herbs and fennel.

bottle of Breaking Bread Winery Grenache Redwood Valley 2019

Breaking Bread Winery Grenache Redwood Valley 2019 ($24)

Breaking Bread’s juicy Grenache ferments whole-cluster with carbonic maceration, giving it a shiny berry pop. The wine ages in neutral oak for seven months before being bottled unfined and unfiltered. Its aromatics suggest ripe cherry and strawberry with a hint of mint, and despite its light texture it has a streak of squeaky tannins. This wine takes a light chill.

bottle of Troon Vineyard Kubli Bench Amber Applegate Valley 2020

Troon Vineyard Kubli Bench Amber Applegate Valley 2020 ($33)

Troon’s biodynamic orange wine is a blend of Vermentino, Riesling, and Viognier grapes that spend three weeks on skins. Fermentations are with ambient cultures, and the wine ages on lees for five months in neutral barriques before bottling unfined and unfiltered. It’s deep golden amber and faintly cloudy, with aromas of honey apples, dried apricots, and fresh hay. Juicy stone fruit lifts the palate, and the finish is nut-like and savory.

bottle of Ciavolich Fosso Cancelli Cerasuolo d’Abruzzo DOC 2019

Ciavolich Fosso Cancelli Cerasuolo d’Abruzzo DOC 2019 ($45)

Ciavolich vinifies the Montepulciano grapes with ambient cultures, and, using the salasso method (which the French call saignée), transfers some of the must to terracotta amphorae to finish without temperature control. The wine is bottled unfiltered. It’s a light, tawny tea rose color with amber glints — not quite a rosé, not quite a red.  The palate suggests a medley of fresh and dried fruits and flowers, and it finishes with a refreshingly bitter snap. 

bottle of Newton Vineyard Unfiltered Chardonnay Napa Valley 2018

Newton Vineyard Unfiltered Chardonnay Napa Valley 2018 ($55)

Newton forgoes filtration because they feel it helps emphasize the site-specificity of their wines, although they do use fining agents sparingly. Their Unfiltered Chardonnay is barrel-fermented with ambient cultures, and most of the lots go through malolactic during its year of aging. The wine is substantial, creamy and lavish, with flavors of citrus and melon and highlights of warm spice. 

bottle of Trombetta Chardonnay Gap’s Crown Vineyard Petaluma Gap 2018

Trombetta Chardonnay Gap’s Crown Vineyard Petaluma Gap 2017 ($60)

Winemaker Erica Stancliff leaves her Chardonnay both unfined and unfiltered, but the results are crystal clear. The fruit barrel-ferments with ambient cultures, and the wine spends eight months in French oak, about one-third new, before bottling. It is sunny yellow with a concentrated perfume of lemongrass, citrus, and cultured cream. The palate is savory, slicked with lemon oil and a cooling note of wet stone. The length is amazing.