Today's customer question: What does it mean to 'filter' or 'fine' a wine?
What is filtering?
Filtration makes a wine brighter and clearer by removing excess sediment and haze. Some wineries may decide not to filter their wines because they feel that the unfiltered wines taste better and have superior mouthfeel. There is no single correct answer; winemakers decide for themselves what is right for their product. Some of our red wines are filtered; some are not. Our wine labels and our website wine profiles indicate when a wine is unfiltered and unfined.
Filtering can also remove microbial problems and bacteria that might multiply in the wine after bottling, causing off aromas or secondary fermentations. Wines containing residual sugar should always be sterile-filtered to prevent fermentation as should any wines containing malic acid—both sugar and malic are high energy food sources for microbes. This means that pretty much all white wines should probably be sterile-filtered before bottling, and sterile-bottled (sterile filtration on the bottling line).
Modern cross-flow filters are extremely gentle and cool, efficient (you can walk away from them while they’re operating and they don’t break down as often) and they are a great choice for "green" and sustainable-model wineries. Unlike the old pad filters, where wine is forced through a filtration medium like a paper pad or a cake of diatomaceous earth, cross-flow filtration moves the wine across a ceramic membrane, where it is essentially "pulled through" as filtered product. There are no used cellulose pads, DE (a hard-shelled algae), or crystalline silica to dispose of.
What is fining?
Fining is the process of adding a natural filtration agent directly to the wine, stirring it in, and letting it settle to the bottom of the barrel. Fining agents are usually protein-based and act as a haze magnet, catching proteinaceous matter and haze from dead yeast, and settling it to the bottom of the barrel or tank so the winemaker can rack the wine off the lees (dead yeast sediment) cleanly. Some fining agents, like eggs, are extremely gentle—they settle the lees to the bottom and "glue" it there without affecting the pigment, mouthfeel or flavor of the wine. At the more assertive end of the spectrum, activated carbon will clean up phenolic problems, but will also strip the wine of some of its color, aroma and flavor.
We have not fined a wine in over six years, relying instead on careful racking and gravity flow processes. But these procedures are very, very slow—at larger wineries it is just not efficient, and white wines in particular are frequently fined to aid in clarification.
There are dozens of historical and modern fining agents, including milk and casein, isinglass, bentonite, irish moss, bull’s blood, egg whites, bone gelatin, algae derivatives, and activated carbon.
Bentonite is a clay formed from ancient layers of ash. It is sold as a natural foods supplement for intestinal cleansing and toxin removal. It comes in a large bottle of suspended clay in liquid, and if you get the peppermint flavor, it’s not bad.
Gelatin and bull’s blood were two of the earliest recorded fining agents. Gelatin was produced (as is most modern gelatin) from boiling bones, like a beef consommé.
Isinglass is another common fining agent derived from sturgeon bladders. Historically, a "fish glue" made from the bones of certain fish, and specifically the air bladder membrane, have been used since the 17th century to bind books. It was also mixed into pigment or gold leaf as a binding agent before painting a parchment or fresco. It is still used to restore and repair ancient parchment. It is also frequently used by pastry chefs to create delicate confections.
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