One metric that high quality red wines are often measured on is color. The ultimate goal is to achieve a deep, rich purple but this can prove more difficult than it may seem. The decisions made by the winemaker in the first several weeks post harvest will determine the ultimate level of color extraction and stability. Each grape varietal and batch has some limit to the depth of color achievable but as a winemaker, you can have a great deal of influence in achieving the most from your grapes.
Two key areas that a winemaker can influence are color extraction and color stability. Good extraction with poor stability leads to light colored reds and the same goes for good stability but poor extraction. Below are several techniques to help improve overall color.
Techniques for Improving Color Extraction
Cold Soak
After crushing your grapes, you may choose to perform a cold soak to extend the time on the grape skins. This will allow water soluble pigments to dissolve before alcoholic fermentation. The steps to performing a cold soak are as simple. Crush and destem as usual but take measures to keep the must cool (50°F to 60°F) and wait several days to innoculate with your yeast. Frozen (and sanitized) water jugs or dry ice are effective for cooling smaller batches. The benefit of dry ice is that it also creates a blanket of CO2 over the must. A cold soak generally lasts only several days but can last up to a week. If performing a cold soak, don't forget to add 50ppm SO2 to ensure that any unwanted bacteria are eliminated.
Note: If wild yeast begin to ferment, you may want to abandon the cold soak and inoculate with commercial yeast sooner. There are many strains of wild yeast and some of which will cause off tastes and odors in your wine, so it is generally preferable to use a commercial yeast. Most commercial yeasts are simply wild yeasts that have been known to produce good results, and have been isolated and offered in various sized packets. A few favorites are Lalvin EC-1118, RC-212, and BM4x4.
Frequent Punch Downs or Pump Overs
Punching down, not only churns up the skins to improve color and flavor extraction, but also prevents mold from forming on stagnant skins. Punch down by submerging the cap of grape skins two to three times a day until pressing. A small batch of wine can easily be punched down with a stainless serving spoon. Large wineries use a hose and pumping system to pump wine from the bottom of the tank to the top, effectively achieving the same result.
Extended Maceration
Much like a cold soak, performing an extended maceration gives the wine more time on the skins, to assure that every last bit of purple is extracted. Additionally, extended maceration allows more tannin extraction from the seeds, which can improve color stability. Extended maceration simply involves leaving the wine to soak on the skins for around one to three weeks beyond the end of primary fermentation. During extended maceration, the wine will no longer be protected with a blanket of CO2 as it is during fermentation but the tannins will offer some protection from oxidation. Depending on the length of maceration, consider blanketing the must with inert gas (Argon, CO2 or Nitrogen).
Fermentation Enzymes
Enzymes are helpful in breaking down the grape cell walls and achieving maximum extraction. There are many commercial enzymes available. A common general purpose enzyme is pectic enzyme which breaks down pectin in the fruits and helps release color and flavor. An even better enzyme, specifically formulated for red wines is Lallzyme EX, which improves color intensity and stability.
Skin to Juice Ratio
A higher skin to juice ratio will yield better color. Varietals with small berries like cabernet sauvignon naturally have a better skin to juice ratio. To improve the ratio, pump off a portion of the juice shortly after crushing. The pump off juice can be then used to make a rosé or blush style wine.
Fermentation Temperature
Warmer fermentation leads to better extraction. Red wine is often allowed to spike to the 85°F to 90°F range to maximize color and tannin extraction. As a side effect, many overly fruity aromas are blown off, which can be good or bad, depending on what your overall goal is for the wine. A seed heater placed on the side of a six gallon bucket will increase the fermentation temperature by around 10°F.
Yeast Choice
Different yeast strains ferment with varying levels of vigor and fermentation speed. Choosing a less aggressive yeast strain can improve extraction by extending the primary fermentation by several days.
Techniques for Improving Color Stability
Fermentation Tannins
Anthocyanins which are the main source of color in red wine can fall out of solution. Short chain tannins bind with anthocyanins, helping to trap them into solution and creating a silky mouth feel in the process. Adding fermentation tannins, like FT Rouge when crushing will ensure that there are enough tannins early in the fermentation to retain your color.
Oxygen at The Right Time
Some oxygen is necessary to encourage the bond between anthocyanins and other proteins or tannins. During cold soak, the wine can tolerate significantly more oxygen than after fermentation and some oxygen at this time is beneficial to color stability. Fermentation is highly reductive (the opposite of oxidative), so this oxygen will be consumed up by the yeast and will help promote a healthy fermentation. During the time of pressing, the wine will absorb a small bit of oxygen once again, which can help catalyze the color stabilizing reaction. After pressing, however, great caution should be taken to limit the exposure to oxygen. In a barrel, a process known as micro oxidation can help cross-link short chain tannins into polymeric tannins but larger doses of oxygen can kick off bad bacteria or create oxidized flavors and browning.
Concentrate Based Solutions
Though highly controversial and rarely spoke of, many commercial wineries use a highly concentrated, grape based formula to boost color in wines that are lacking. One such product is Mega Purple which not only masks off flavors but boosts color significantly. If you are drinking a store bought wine that seems unnaturally dark, there is a good chance Mega Purple was used.
Common Practices and the Effect on Color
Many winemaking operations can have a negative impact on wine color and it is important to understand the potential result of such activities.
Activated charcoal is occasionally used to remove off flavors from wine. In too high of dosage, activated charcoal can rob a wine of some or even all of it's color. Avoid using any barrels or oak products with a "char" and stick to toasted oak products for this reason.
Stirring the fine lees (bâtonnage) is a common practice in white wine making and helps to improve mouth feel but can strip color in red wines.
Aggressive fining or filtering will have a subtle effect on color and character but is commonly practiced to ensure microbial stability.
Acid additions or reductions will cause a shift in color. High acid wines look more pink and transparent, while low acid wines look more purple/blue and translucent.
Summary
As a winemaker, many of your decisions can cause a ripple effect related to wine color. The best wine isn't necessarily the darkest, but there is a perception that darker is better by many consumers. In general, most processes that improve the color are beneficial to other wine characteristics such as mouth feel, longevity, aroma, or taste. By understanding the relationship that each process has on wine color you can achieve, not only an outstanding wine, but a wine with great visual appeal to please those pesky judges.
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