The Beer Brewer

Processing of the grapes occurs soon after harvest, with whole bunches, (still containing stalks to aid drainage) being crushed in a roller crusher, before immediate pressing occurs, to reduce the extraction of phenolic compounds (expressed as gallic acid equivalents), which produce ‘rough’ or uncharacteristic tastes in the finished wine at concentrations greater than 850mg l-1.  Batch pressing is often utilized in modern establishments, as opposed to the more traditional screw pressing in vats (lagares) after treading occurred. Batch pressing allows juice to initially drain freely from the solids. This ‘free drain’ juice contains up to 200mg l-1 of total phenolics, and is kept separate from other pressed juice, and used primarily in the production of fino style Sherry. Further screw pressings in the batch process yield more juice (48% of total), although increased levels of tannic material are extracted. Extracts containing total phenolics to levels of 850mg l-1 are used to produce oloroso or associated Raya type wines, as the higher levels (of phenolics) assist in the subsequent oxidation of the wine. Extracts containing polyphenol levels of greater than 850mg l-1 are not used to make Sherry.
Prior to fermentation, juices are cooled to 12 - 15°C, to facilitate the settling of solids, thus maintaining low total solid levels (1%). Tartaric acid may be added to correct pH levels to approximately 3.45. Sulphur dioxide may be added to 100mg l-1 to inhibit undesirable spoilage microorganisms (predominantly the Lactic Acid Bacteria), and to prevent browning.