glossary oF Portuguese anD teChniCal terMs 279Fining: the process where microscopic particles are removed from a wine by the addition
of a fining agent. The most commonly used fining agents are bentonite, casein, egg
white, or gelatin, which adsorb or coagulate with potentially unstable colloidal material
suspended in the wine, causing it to precipitate more quickly. The fining of Port is
discussed on p. 145.
Pectolitic Enzymes: used by winemakers to break up natural pectins in the grape skins and
occasionally to aid colour and flavour extraction.
pH: hydrogen power; a measure of the concentration of the acidity. Low pH indicates high
concentrations of acidity and vice versa. All grape must is acidic, usually registering pH
values between three and four. The scale is logarithmic, so a wine with a pH of three
has ten times as much hydrogen ion activity as one whose pH is 4. Most Douro grape
musts are naturally at the upper end of the spectrum (occasionally in excess of pH4)
and have to be corrected by the addition of tartaric acid (see also Total Acidity).
Phenolics: a large group of reactive chemical components responsible for the tannins,
pigment (anthocyanins) and many of the flavour compounds found in wine. Most of
the phenolics come from the skins of the grape.
Sulphur Dioxide (SO^2 ): a disinfectant and anti-oxidant used by winemakers. The efficacy of
sulphur dioxide is influenced by the wine’s pH.
Total Acidity: a measure of both fixed and volatile acids in wine usually expressed in Portugal
as grams per litre tartaric. The ideal range for grape musts is between 7 grams per litre
and 10 grams per litre with wines varying between 4.5 grams per litre and 8 grams
per litre. Port naturally tends to be towards the lower end of the spectrum with musts
registering as little as 5 grams per litre expressed as tartaric acid. The addition of tartaric
acid is therefore commonplace.
Volatile Acidity: a measure of the naturally occurring organic acids in a wine that are separable
by distillation. The most common volatile acid in wine is acetic acid, which imparts a
vinegary character if present in excessive concentrations. The Portuguese use the term
vinagrinho (‘little vinegar’) to describe a wine with noticeable but not detrimental levels
of volatile acidity (usually found in old colheita and tawny Ports).