Skin fermentations

The three treatments were immediate press, hot press (60 °C for 15 min), or skin fermentation (7 and 13-14 days). Total phenolics were measured as gallic acid equivalents (GAE) /L and were separated and measured by HPLC (Lamuela-Raventos and Water-house, 1994). A Perkin Elmer HPLC quaternary pump (Model 400) was fitted with a Rheodyne 7125 injector and Waters Novapack C18 (30 cm x 0.39 cm., i.d., 4 yum particle size) column. A diode array detector (Perkin Elmer model LC 135) was connected to a Perkin Elmer Model 1022 integrator. The solvent system used was described earlier (Lamuela-Raventos and Waterhouse, 1994). 

The results obtained in our studies showed that the concentration of total phenols of both Vitis vinifera cv. Cabernet Sauvignon and Vitis rotundifolia cv. Noble wines increased with increasing skin fermentation time. These concentrations varied significantly from 831 to 821 mg/L GAE (from 7 to 14 days) for Cabernet Sauvignon and from 1096 to 1269 mg/L GAE (from 7 to 14 days) for Noble. However, in Chambourcin wines, the concentration of total phenols decreased significantly with increasing skin fermentation time (from 971 to 699 mg/L GAE). 

Chambourcin, coutaric acid was able to be quantified in all treatments except in 14 day skin fermentation wine. Increasing the skin fermentation time significantly decreased the coutaric acid concentration. In Noble, coutaric acid was present in very low levels in all skin fermentation wines. 

Ellagic acid in Noble wines did not increase with skin fermentation time. Previous observations (Oszmianski et aL, 1986) indicated that extended skin fermentation time increased the precipitation of ellagic acid sediment. Therefore, skin fermentation could have increased the extraction of ellagic acid, but most of this ellagic acid may have precipitated. 

Increasing the skin contact time increased the extraction of catechin and procy-anidins in Cabernet Sauvignon, with 14 day skin contact wine having the highest content of catechin and procyanidins. Catechin and procyanidins remained stable from 7 to 14 day skin fermentation time. Procyanidin B8 remained almost stable from 7 to 14 days skin contact. 

In Noble, skin contact increased the extraction of procyanidin B3, but catechin and procyandin B8 decreased with increasing skin fermentation time. One explanation could be that catechin and procyanidin B8 were subject to oxidation or further polymerization. Overall, the levels of procyanidins and catechin in Noble were very low compared to Chambourcin and Cabernet Sauvignon. 

When comparing cultivars (7 days skin fermentation wines), it can be seen that Chambourcin is not as astringent as Cabernet Sauvignon, which was probably related to the lower content of procyanidins in Chambourcin compared to Cabernet Sauvignon. However, Noble wine, which had the lowest content of procyanidins, was rated as the most astringent and bitter. This evidence was probably due to the presence of extremely high amounts of gallic acid and epicatechin. 

Extended skin contact treatment did not result in tannic wines and could produce wines with good color stability (Sims and Bates, 1994). However, some species or cultivars (such as Vitis rotundifolia) may not be suitable for extended skin fermentation, since they may not possess the type of phenols and/or anthocyanins that will polymerize, and consequently soften and provide color stability (Sims and Morris, 1985). 

Skin fermentation time had no significant effect on pH, but titratable acidity increased slightly (by 0.05-0.1 g/100 mL) with increasing skin fermentation time for red muscadine wines (Lin and Vine, 1990). However, total acidity and tartaric acid content decreased and pH increased with skin contact on Vitis vinifera grapes (Ricardo da Silva et ah, 1993). All of the Cabernet Sauvignon wines had higher pH than Chambourcin and Noble wines. 

Sims, C.A. Bates, R.P. Effects of skin fermentation time on the phenols, anthocyanins, ellagic acid sediment, and sensory characteristics of a red Vitis rotundifolia wine. Am. J. Enol. Vitic. 1994, 45, 56-62. 

Port-type ted dessert wines require skin contact time to extract the anthocyanins, but the fermentation must be short to retain the sugar level neat the 6—10% level desired. The winemaker cannot always achieve desired composition in individual lots. In order to teach the desired standard, it is necessary to make new lots to enable blending to that standard. The right volume of a tedder, less sweet wine will need to be made to bring to standard a lot with low color and mote sugar, for example, while keeping the alcohol also within the desired limits. 

In the wet method, as practiced in Colombia, freshly picked ripe coffee cherries are fed into a tank for initial washing. Stones and other foreign material are removed. The cherries are then transferred to depulping machines which remove the outer skin and most of the pulp. However, some pulp mucilage clings to the parchment shells that encase the coffee beans. Fermentation tanks, usually containing water, remove the last portions of the pulp. Fermentation may last from twelve hours to several days. Because prolonged fermentation may cause development of undesirable flavors and odors in the beans, some operators use enzymes to accelerate the process. 

Another variation which attempts to place the test upon a semiquantitative basis involves carrying out the reaction in a Smith fermentation tube. This enables one to obtain a rough idea of the volume of gas formed, but it can be misleading unless a time limit is imposed and the skins are removed. 

The complexity of wine composition is a central reason for the vast variety of wines in the marketplace. In addition to water and ethanol, the major components, a variety of organic acids as well as metal ions from minerals in the skin of the grape are present. Initially, all of these substances remain dissolved in the bottled grape juice. As the fermentation process occurs, the increasing alcohol concentration in the wine alters the solubility of particular combinations of acid and metal ions. Unable to remain in solution, the insoluble substances settle as crystals. Since the process of red-wine making involves extended contact of the grape juice with the skins of the grapes (where the minerals are concentrated), wine crystals are more common in red wines than in white wines. 

After initial development the dough is fermented for hour or an hour and a half at around 24—28°C. The dough is then knocked back three-quarters of the way through proving. Next the buns are moulded to size and proved in a cool prover with steam to prevent skinning. The products are then baked, possibly at 210 220°C. 

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