Phenolics are complicated plant-derived compounds based on the phenol molecule, a benzene ring with a hydroxyl group attached. Phenolic compounds are responsible for or have a significant influence upon wine color, taste, and mouthfeel. Phenolic content in grapes is determined by grape cultivar, climatic conditions, and vineyard and winemaking practices. The polymerization of grape phenols provides tannins. These tannins provide antioxidant properties, mid-palate texture and help stabilize color by condensing with anthocyanins to create polymeric pigments.
Unfortunately, nature does not always provide ideal conditions for phenolic development in the vineyard or for phenolic extraction during winemaking. The following are tools that may be used from the vineyard through winemaking to enhance the phenolic structure of wines.
At the crusher or fermenter, maceration enzymes may be added to speed up the extraction of tannin and color in the fermenting or coldsoaking must. This can speed up the stabilization of color. In the case of infected or unripe grapes, it will enable the extraction of color and tannin early on so that the juice can quickly be separated from moldy or “green” solids.
At the crusher (or press for whites and rosés), enological fermentation tannins may be added to Vitis vinifera grapes if the grapes are known to be lacking in tannin, have a weak mid-palate or contain rot. The addition of FT Rouge or FT Rouge Soft at the beginning of fermentation also helps preserve the grapes’ natural tannins so they can combine with anthocyanins for optimal color stability.
When dealing with hybrid grapes, studies from Cornell University have shown that the presence of “parthenogenesis related proteins” cling tightly to grape tannins and resist releasing them into the wine. These proteins also bind with enological tannins, rendering them less effective in the fermenter. In this case, the winemaker is probably better off concentrating on cellaring and finishing tannin additions after the wine has been separated from the grape solids.
Although there is a debate about the effectiveness of cold soaking prior to fermentation, many winemakers are firmly committed to the practice. They feel that with the early extraction of color and tannin, they end up with better structure and faster stabilization of color. One negative aspect of a cold soak is the potential for unwanted microbes to infect the must. To avoid this, there is Gaia. Gaia is Metschnikowia fruticola, a non-fermentative yeast that is added to the must at the onset of the cold soak. It quickly populates the must and prevents wild yeast, such as Kloeckera apiculata, from growing and producing VA (volatile acidity).
FERMENTATION AND COLOR
During the fermentation of Vitis vinifera red grapes, enological tannins derived from grapes (Uva’Tan or Uva’Tan Soft) or quebracho trees (FT ColorMax) may be added to start the early stabilization of color. It is recommended they be added ⅓ of the way through fermentation when there is a sizeable pool of aldehydes in the fermenting must. These aldehydes will act as bridges during tannin polymerization and anthocyanin condensation. The aldehydes are a two carbon link between the tannins and anthocyanins.
As mentioned above, for hybrids the tannin addition will probably be most effective when done post fermentation as cellaring or finishing tannins. Oak and chestnut tannins (ellagic tannins) do not have a direct effect on the stabilization of color beyond their use as antioxidants.
PH AND COLOR
pH has a strong effect on red wine color. A lower pH moves color into the red range. There will also be higher levels of colored anthocyanins. At a higher pH, there are fewer colored anthocyanins and they move more toward blue.
AGING AND CELLARING
As V. vinifera red wines age, harsh tannins soften and anthocyanins diminish as polymerized pigments increase. During cellaring, enological tannins can be added to wines that may be lacking. This may be achieved through aging in oak barrels, using oak barrel inserts, the addition of oak chips or cubes, or with the addition of cellaring tannins derived from oak (untoasted or toasted), grapes, quebracho, or blends thereof. Small additions (~50ppm) of enological tannins during racking and transferring wine can scavenge oxygen and help prevent oxidation.
With hybrids, several additions of enological tannins during aging can build mid-palate and help stabilize the very high levels of color that many hybrids contain. For color stabilization, either grape (Uva’Tan) or quebracho (FT ColorMax) tannins should be used.
The temperature of aging plays an important part in wine development. Very cold temperatures can cause the precipitation of unstable colloidal color. Cool temperatures will promote the slow development of polymerized pigments. Warm temperatures can cause anthocyanin breakdown reactions.
In young white wines, brown or amber color may develop due to oxidation of small phenolic compounds. This may also cause phenolic bitterness. Treatment with either PVPP (Polycel) or casein (Caseinate de Potassium) can remove the bitterness and restore the color. In some whites, high acid can make the wine acidic and harsh. The addition of gall nut white tannin (FT Blanc Soft) can help build mouthfeel and soften mid-palate perception.
The last steps prior to bottling may involve nothing more than stabilization and a final SO2 addition. However, many wines need tweaking to bring out their full potential. If a red wine still contains harsh tannins after barrel or tank aging, one possible treatment is fining with gelatin (Colle Perle or Inocolle) while counter-fining with silica gel (Gelocolle) to aid settling and prevent over fining. As with any fining, bench trials are necessary to determine the correct dosage.
Another treatment to rectify tannic harshness is a pre-bottling addition of gum arabic (Flashgum R or Inogum 300). Gum arabic reacts with and softens harsh tannins. It also has protective colloidal effects which are especially important with colloidal (non-stabilized) color. The gum arabic coats the anthocyanins and helps prevent them from precipitating. This addition should not be done until the wine is bottle ready. Fining and stabilizing need to be done prior to gum arabic addition. Most finishing tannins should be added 4–6 weeks before bottling to be sure that there will be no instabilities or sedimentation. However, there are also some very highly refined tannins (Luxe tannin range) that can be added up to 48 hours prior to bottling. Often a combination of the tannin with either gum arabic or a mannoprotein/gum arabic blend (Ultima Soft or Ultima Fresh) works to significantly increase mouthfeel and create a softness at the same time.