Color and tannins

The problem of color due to tannin can be annoying, although not insurmountable. For small, simple boiler plants, the presence of color is, in fact, a benefit, as the depth of color is more or less related to the inhibitor concentration and the BW conductivity and TDS levels. Where multiblended formulations are employed, if the color is within range, then other parameters are also likely to be acceptable. Also, electrical conductivity is unaffected by color, and tannins do not appreciably add to the measurable TDS of the BW. 

European special-purpose rotating tanks have been used successfully by at least one North Coast winery, but the cost of the equipment and space required has discouraged expansion of this facility. Continuous fermentation systems have been introduced in foreign countries but are only in very limited use in northern California. Dangers of contamination, cooling difficulties, and the need for a continuous flow of must make them unsuited for premium wine production. Heating is another way to liberate color and tannins from the skins but until recently all experiments have produced wines of inferior quality and, therefore, have not been used in the coastal counties of California. 

In the past decade, some North Coast wineries have experimented with a completely anaerobic fermentation technique known as carbonic maceration. In this system, whole grapes are placed in a vat and fermentation is allowed to start. Since there is no pumping over or aeration, the fermentation proceeds very slowly under a blanket of carbon dioxide. The fermentation relies upon the intercellular production of ethanol to kill the skin cells and release the color and tannins. The results are claimed to be wines with a special bouquet, earlier maturity, slightly more alcohol, and a softer taste. They are easily recognizable by their special bouquet. Although popular in France, where they are drunk very young, they have not gained widespread acceptance with the North Coast wineries. 

Hilgard, E. W. The extraction of color and tannin during red-wine fermentation. Calif. Agric. Exper. Stat. Bull. 1887,77,1-3. 

Berg, H.W Akiyoshi, M. The effect of contact time of juice with pomace on the color and tannin content of red wines. Am. J. Enol. Vitic. 1956, 7, 84-90. 

Deshpande et al., 1982 Price et al., 1980). It appears from these reports that white-seeded strains contain no detectable tannins compared to colored seeds. Ma and Bliss (1978) reported that tannins were mostly associated with the testa layer of common dry beans, and that black seeds were usually higher than other seeds in tannin content. Although black seeds contained more tannin, few plants with colored, non-black seeds had high tannin contents. These observations were later supported by Deshpande et al. (1982). Similarly, several researchers (Thayer et al., 1957 Blessin et al., 1963 Stephenson et al., 1968 Harris, 1969 Damron et al., 1968 Mabbayad and Tipton, 1975 Nelson et al., 1975) reported no direct relationship between pericarp colors and tannin contents of grain sorghums. 

White wines are generally fermented at lower temperatures (10°G/50°F to 18 G/65 F) for better aroma retention, whereas red wines are fermented at higher temperatures (18 G/65 F to 29 G/85 F) for increased color and tannin extraction (Ough and Amerine, 1966). Peynaud (1984) recommended slightly different fermentation temperatures, 18°G/65°F to 20 G/68 F for making white and rose wines and 26 G/79 F to 30°G/86°F for red wines. Margalit (2004) suggested that white as well as rose and blush wines be fermented at even cooler temperatures, 8 G/46 F to 14°G/57°F, whereas red fermentation should be conducted at 22 G/72 F to 30°G/86°F. 

Other biochemical phenomena probably accompany this artificial overripening. Wines obtained from these treated grapes are richer in color and tannins and are always preferred at tastings. This treatment is exclusively for red winemaking, since the resulting increased phenolic compound concentrations are detrimental to quality white winemaking. 

Table 12.4. Influence of pumping-over on color and tannin dissolution in open fermenters (Sudraud, 1963)...

The quahty of individual gums is mainly deterrnined by color and taste or odor. Many gums are colorless when secreted, but darken on aging. Most gums are usually tasteless unless contaminated by the bitter flavors of tannins which precludes their use in foods. 

A study of the effect on the congener levels of up to eight refills of a used whiskey barrel iadicate that volatile acids, esters, colors, soHds, and tannins showed the greatest percentage change between the first and second use of a new charred barrel (11). 

GMP) quantum satis) presence of ethanol and tannins least used caramel color... 

Dioscorides also notes that numerous plants or parts of plants, as the bark, leaves and roots of the oak, nutgalls, sumac, etc., contain a substance sour and astringent, which is used in medicine and for tanning leather, and for coloring and darkening the hair. The tannin, which is the essential constituent, was not, however, more definitely identified. It will be recalled that in the form of juices or... 

Metals and Tannin. — On adding to 10 cc. of alcohol 1 cc. of ammonia water or 5 cc. of hydrogen sulphide water, no coloration should develop. 

Antbocyanin and Tannin Analyses y Determination of Wine Color... 

The first method uses the fact that in acid media anthocyanins exist in a colored and a colorless form (9 and 10) in equilibrium, with the position of the equilibrium depending on pH. Consequently, the difference in color intensity between the two pH values (0.6 and 3.5 for example) is proportional to the pigment concentration. Since the phenol function is not affected by this variation, other phenolic compounds, especially tannins, do not interfere since their absorption at 550 nm is the same at both pH values. 

---