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.

Clarity

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

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.

Suspensions

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.

Color

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

Available mechanisms for ameliorating tannin-associated wine imbalance

In a previous post on tannins and wine balance, I noted that too much tannin results in a wine that is heavy and rough on the palate and lacks finesse.  Further, if combined with high acidity, the wine will be astringent.  While low levels of tannin may result in an early drinking wine, it may compromise color stability, mouthfeel, and the aging potential of the wine.  This post looks at the tools available to the winemaker to increase/decrease tannin levels as desired.

Increasing Tannin Levels

Tannin levels can be elevated by manipulating aspects of the winemaking process to extract more tannin from a given batch or by adding exogenous tannin during the winemaking process.

The primary integral process for elevated tannin extraction is maceration.  The length of the maceration, and the controlling temperature, are two very important variables in determining tannin extraction levels.  The longer the duration, the higher the levels of tannin and anthocyanin extracted. The higher the temperature (within limits), the higher the tannin extraction rate.  With the higher levels of phenolic compounds that result from post-fermentation maceration, the greater the potential for phenolic polymerization and wines with a softer mouthfeel.

While maceration can be used to extract tannin from both skin and seed, warm processing is a method wherein a quick, hot fermentation is applied to allow extraction of tannin from the skin while minimizing seed contact.

Exogenous tannin addition can be oak (or like products) or powdered.  In the case of oak, the wine is either placed into oak barrels or oak powder, chips, or planks are placed into the container in which the wine resides (The role of oak tannin was discussed in the preceding post.).  Powdered tannin is the end product of mechanical action on grape seeds or various types of wood.  A recent study by Washington State Enologist Jim Harbertson and Australian Wine Researcher Mark Downey called the efficacy of the latter approach into question.  Their key findings were: (i) most of these additives are 12%-48% tannin and (ii) had limited or negative impact on wine quality.  They concluded that the addition of powdered tannin was an unnecessary expense.

Retarding Tannin Levels

"Cold soak" is a method that is utilized in the winery to extract anthocyanins from the grape skin while restricting the level of tannin extraction.  Anthocyanins are more soluble in grape juice than in alcohol so soaking the solids in the juice at 45℉, or lower, will retard the initiation of fermentation while allowing the extraction of color from the skin and limiting the tannin extract.

Fining is a method of clarifying or chemically stabilizing wine using agents that are insoluble in the liquid, have the ability to bind with suspended particles, and are heavy enough to fall to the bottom while retaining the attracted material.  Tannins have an affinity for proteins and protein fining agents such as gelatin, egg white, and isinglass are used to remove tannin from the wine in this manner.  The fined wine is racked off the bottom-resident particles.  Care has to be taken that the wine is not over-fined as the result may be wines that lack complexity, depth, and viscosity and have diminished aging potential.

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In addition to raising or lowering tannin levels, tannin-associated wine imbalance can be addressed by actions taken in relation to the other elements of the balance equation.  For example, reducing the acidity levels in high-tannin, high-acid wines will reduce the level of astringency in the wine.  In addition, increasing the level of alcohol in a wine will increase its bitterness but will also reduce the sensation of astringency.  Astringency is also decreased with increasing wine pH.

Hopefully the winemaker will be presented with grapes with the appropriate amount of tannins to ensure the production of balanced wines but if he/she is presented with an excess or surfeit of tannins, the above mechanisms are available for amelioration.

© Wine -- The View From Orlando