Wednesday, April 4, 2012

Appearance as an indicator of wine quality

I recently developed and reported on a framework for the assessment of wine quality, a position at which I had arrived rather tangentially.  I was writing a post on wine balance as a quality measure and, upon concluding, realized that I had not defined quality as a concept or wine quality as an ideal.  Over the course of two subsequent posts I corrected these oversights and then returned to the task of elaborating the components of balance as contributory inputs to wine quality.  My starting point for these discussions, as shown in the quality assessment model below, was fairly "deep in the belly of the beast."  In my future posts on this topic I will be working in a more structured, top-down manner beginning with today's post on appearance as a wine quality marker.

There are two main factors to be considered when visually assessing a wine in terms of quality: clarity and color.


According to the WSET® standards, clarity can be categorized as either clear or dull.  Most of the wines available commercially are pretty clear because, especially in the U.S. market, there is a "finickiness" about consuming products that are cloudy, or dull, or impregnated with suspended particles.  The factors which can contribute to dullness in a wine include: cloudiness/haze, bubbles, and suspensions.


Cloudiness, if not the specific intent of the winemaker (e.g., Scholium Project, selected Gravner wines), could be the result of improper racking/clarification or protein instability.  Most wineries rack their wines from container to container in order to separate it from solid elements that have sedimented out of solution (There is, of course, an oxygen-exposure element to some racking but that is outside the scope of this discussion.).  Intuitively, there will be higher concentrations of large solids sedimenting out of the wine in the earlier stages of storage and then slower sedimentation rates with the passage of time as fewer and fewer large pieces of insoluble material remain in the wine. Some wineries will introduce fining agents such as egg white, bentonite, or isinglass which bind with proteins and fall to the bottom of the containment device.  Some of the flavor elements in the wine exists as solids and some winemakers refuse to fine because of fear of this process diminishing the wine's flavor profile.  If racking and fining does not clear up the wine, the winemaker may resort to filtration.  Again, many purists decry filtering because of fear of "flavor-napping."

A second potential source of cloudiness in wine is protein instability.  According to Dr. Bruce Zoecklein, Enologist at Virginia Tech (and my go-to guy), the major source of protein in wine is the grape and amounts can range between 10 and 275 g/l (Protein Stability Determination in Juice and Wine). White wines have large insoluble proteins which precipitate out of solution imperceptibly.  The more rapid precipitation, which is visible as protein haze, is, according to Dr. Zoecklein, probably the result of protein-flavonol bonding.  Addition of bentonite in the winery can eliminate this protein haze.  Some of the proteins in the solution may precipitate out if the wine bottle is subjected to heat and would manifest as the cloudiness/haziness that would render the wine's quality suspect in the eyes of the consumer.

Secondary Fermentation

If the wine is not a Vinho Verde (young, easy-drinking wine from the Minho region of Portugal), or a designated sparkling wine, it should not contain bubbles.  Bubbles in a still wine is an indication of secondary fermentation in the bottle, a situation that occurs when the wine is bottled while still containing appreciable levels of residual sugar and viable yeast cells.  Under the appropriate conditions, the yeast will begin to ferment the residual sugar (because that is what yeasts do) producing alcohol and releasing carbon dioxide in the process.  Given the anaerobic environment within the bottle, the carbon dioxide dissolves into the wine and will alert to its presence either by pushing the cork up through the capsule, causing the bottle to explode, or manifesting as bubbles when the wine is poured into a glass.


One potential suspension in a wine glass is sediment.  Now sediments are, of course, not harmful if ingested but if encountered in a glass poured in a restaurant the consumer should be teed off.  As wines age, pigments precipitate out and fall to the bottom of the bottle.  Ending up with a mouthful of sediment is an unpleasant feeling and is one of the reasons that older wines should be carefully decanted before being poured into wine glasses.

Another "deposit" which can sometimes be found in wine is tartrate crystals (sometimes called wine diamonds).  Wine contains both tartaric acid and potassium and under cold conditions they combine to form potassium bitartrate crystals.  These are harmless but unattractive to U.S. consumers so winemakers cold stabilize the wine in stainless steel tanks to force the crystals to form in a controlled environment.  The crystals formed in this manner adhere to the sides of the stainless steel tanks and the wine is then poured off leaving the crystals behind.  If a wine is not cold stabilized prior to bottling, tartrate crystals could precipitate out if the wine is subjected to very cold conditions.  Scch crystals, when they occur, are normally found on the underside of the cork or suspended in the wine.


According to the Wine Spectator (Inside Wine: Color), consumers associate darker-hued red wines with greater quality and winemakers are responding to this perception by pursuing viticultural and vinicultural practices that result in wines with the color the customers are demanding.

The color in red wine comes from pigments called anthocyanins which reside in the skin of the berry and provide the red, blue, and purple colors associated with the fruit.  Red varieties such as Syrah, Cabernet Sauvignon, and Petite Sirah have higher anthocyanin concentrations than do varieties such as Pinot Noir and Nebbiolo.  Viticultural techniques such as yield reduction, foliage removal, and control of vegetative growth can yield grapes with darker color while vinicultural practices such as pre-fermentation cold soak, pumping over, andy punching down all seek to extract as much color (tannins and flavor) as possible from the skins (White wines are not generally brought into contact with their skins).

In general, white wines are colorless when young, gaining a brownish tint as it ages.  Red wine should be purple to ruby when young, browning as color sediments out. A young wine with a brown color could be manifesting the effects of oxidation.

© Wine -- The View From Orlando

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