Dirt Can Make Wine Better

After spending time in the vineyard these past two weeks, irrigating, spraying, clearing weeds, and watching the grapes begin to turn from vivid green to soft pink and purple colors (veraison), I began to once again think about the upcoming harvest and the many tasks that will be required to convert these 2019 grapes into a wine and put that wine into a bottle.  It is certainly true that the dirt in which the vines are planted plays a role in generating the quantity and quality of the fruit, but there is another type of “dirt” that plays a role in making quality wine.  That dirt is an activated clay material (a special kind of dirt) known as bentonite.  Bentonite is used in winemaking to clarify wine by attaching to particulate materials and to protein molecules that come from grapes.  Bentonite has myriad other uses, including: moisture absorbent in cat litter, thickening agent in drilling muds, binder material in metal casting, water-barrier sealant layers for ponds and landfills, and, with its powerful absorbing properties, a purification & decolorizing agent for numerous liquids, like vegetable oils, dirty water and many beverages. 

When wine grapes are crushed and/or pressed to separate juice from solids, lots of minute solid materials remain suspended in the liquid, making it very cloudy (sort of like lemonade).  Given time, most of these suspended particles will precipitate to the bottom of the tank or container.  However, by adding a measured amount of bentonite in aqueous slurry, those suspended solids will attach to the bentonite clay and readily precipitate, leading to essentially clear juice or wine.  Efficient and rapid clarification of wine is a key use of bentonite. 

Bentonite will also attach to and absorb relatively large amounts of protein molecules that are present in aqueous solutions, like wine.  If these protein molecules are left in the wine, exposure to warm temperatures can denature the proteins and cause them to create annoying flocculent clouds or hazes in both red and white wines.  Consequently, bentonite is particularly useful in the process of heat stabilizing wines so they will remain clear and bright.  Winemakers typically treat wines with bentonite, and then heat a sample at a certain temperature for a prescribed period of time to check for haze formation. 

Most high-grade natural bentonite comes from the northwestern states of South Dakota and Wyoming.  Additional sources of bentonite in the U.S. include Georgia, Mississippi and Alabama.  Other countries, such as Turkey, Greece, Australia, India, Russia, and the Ukraine produce significant amounts of commercial bentonite. 

It is unlikely that you will encounter wine with haze or cloudiness from denatured proteins due to incomplete heat stabilization.  Winemakers today tend to make very good use of bentonite and related materials to manage this problem.  It is, however, becoming more likely that you may encounter wines with some cloudiness due to the growing popularity of producing non-filtered wines.  For example, most Pet-Nat sparkling wines that have become quite common in Texas are not filtered and are cloudy.  Many will have a noticeable powdery-like sediment in the bottom of the bottle.  This sediment is primarily dead yeast cells that produced the sparkle in the wine before dying.  Also, a different type of cloudiness in wine can result from the precipitation of potassium bitartrate crystals that look more like sand and are often called wine diamonds.  This sediment, which is better known as Cream of Tartar, is completely tasteless and harmless, but it sure looks bad.  This occurs as a result of incomplete cold stabilization of a wine such that when cooled or chilled the potassium bitartrate material crystallizes and eventually falls out of solution. 

So, when you visit a tasting room or winery, pay attention to the clarity (lack of haze, cloudiness, sediment, etc.) in the wine in your glass.  If the wine is not crystal clear, there is a reason, and it can generate a fun discussion between you and the winemaker or tasting room associate.  There are lots of pieces and parts to this winemaking game, and understanding more about them can enhance your enjoyment of wine.