146 Port anD the Douro
are used to stabilise and remove oxidative browning from white Ports. Unless there is a
particular problem, old tawnies and bottle-matured wines like unfiltered LBVs and vintage
Ports are rarely (if ever) fined.
Most rubies and young tawnies are cold stabilised to remove tartrates and colouring
material, which could otherwise crystallise and precipitate in the bottle (particularly in
colder climes like Canada and Scandinavia, both of which are important markets). Two
systems are commonly used. The first involves the use of a heat exchanger to refrigerate
the wine down to between -8 and -10°C followed by static settling for about a week in an
insulated tank. Alternatively, most of the larger Port shippers have invested in continuous
systems which chill the wine and pass it continually through a crystallising tank. In each
case, the wines are filtered after the stabilisation process using diatomaceous earth followed
by sheet and/or membrane filters. Smaller producers like single quintas, which lack the
wherewithal to purchase such sophisticated equipment, tend to rely on metatartaric acid,
which merely offers short-term protection against tartrate deposition. Since the increase
in bacteriological problems during the 1980s (see below), shippers have resorted to flash
pasteurisation following cold treatment in order to achieve ‘belt and braces’ stability in
volume ruby and tawny. Wine extracted from the lees is also pasteurised.
The methods of clarification and filtration outlined above inevitably strip a certain
amount of character and flavour from a wine. Consequently, bottle-matured Ports are
not cold stabilised and are rarely filtered, leading to the formation of a heavy deposit or
‘crust’. These wines need to be decanted off the sediment before serving (see page 200 for
decanting recommendations).
quality Control
In the early and mid-1980s there was a rapid increase in the incidence of bacterial problems.
Wines that appeared to be correct in the tasting room suddenly turned unpleasantly volatile
(vinegary) in bottle. Lactic bacteria (lactobacillus), which flourish in the presence of small
amounts of air, will transform naturally occurring malic acid into lactic acid and attack the
glucose in the wine to form acetic acid. In dry red wines and some whites, this malo-lactic
transformation is perfectly natural, leading to a reduction in the overall acidity of the wine.
However, in Port, where glucose levels are high and acidity is generally low in the first place,
the presence of lactic bacteria is always extremely detrimental to the wine. Until the 1980s
many producers believed that these lactic bacteria were unable to tolerate high levels of alcohol
and (particularly up in the Douro) hygiene was perhaps not accorded the highest priority.
Since a number of shippers were caught out with the 1985 vintage (see Chapter 6),
hygiene and quality control have come to the fore. Technical requirements have to be
adhered to and, in response to the decline and subsequent suspension of bulk shipments,
the major shippers have all set up their own quality-control laboratories. The Instituto dos
Vinhos do Douro e do Porto (IVDP) has a well-equipped laboratory and offers its services
to smaller shippers. The IVDP also has its own rigorous quality control procedures but