Agriculture Reference
In-Depth Information
of isinglass, probably because lipids are entrapped in the precipitated proteins.
Isinglass will also work effectively with other fi nings; thus a mixture of silica gel
(xerogel) and isinglass was found to be most effi cient in the clarifi cation of lager
beers prior to fi ltration (Leiper
et al.
2002).
In wine production, isinglass functions without much infl uence on colour or
astringency (i.e. it has little infl uence on polyphenols), whereas gelatin is a better
fi ning agent for over-tannic or over-coloured white wines. In both cases, however,
fi ning is usually carried out immediately before fi ltration and/or bottling. Gelatin is
available in various forms or 'grades', which differ in the molecular weight ranges
of their proteins. Low molecular weight proteins appear to be more selective toward
polymeric polyphenol removal (Maury
et al.
2001). However, accidental over-
fi ning is easily done, especially in the case of white wine, so it is usually used in
conjunction with a silica gel preparation, which not only helps clarifi cation as such
but also assists in the precipitation of gelatin-polyphenol particles, thus preventing
over-fi ning by gelatin (Margolit 2004). The normal regime is to fi ne fi rst with
silica gel, then with gelatin 24 hours later, racking off the deposit a week or so
after that.
Silica gel is a pure, clean fi ning agent that functions without infl uencing
organoleptic properties. It can be obtained as a hydrogel (30% suspension in
water) or as a xerogel (containing 5% water). The former can be used directly for
fi ning white wine, but for beer clarifi cation they are usually slurried in water at the
rate of 15 g per 100 ml. In brewing, silica gel is selective toward haze-active
proteins, with little infl uence on foam-active proteins; it is particularly favoured
by continental European brewers. Like silica gel, bentonite (an aluminosilicate of
sodium or calcium usually) effectively fl occulates net positively charged haze-
active proteins. Although it is used to fi ne new beer, cider or white wine, it is also
widely employed in the clarifi cation of white grape must. One disadvantage is its
tendency to remove aroma compounds if used at too high a rate.
Skimmed milk or potassium caseinate (again with net negatively charged
particles) is likewise useful in the fi ning of white wine, but at the same time it
reduces oxidised brown/yellow coloration and improves organoleptic quality. Egg
white or albumen is the classic clarifi er of red wines, where it reduces astringency
by precipitating some polymeric polyphenols. Many famous European wineries
use no other fi ning agent for their red wines.
All the fi ning agents described above are classed as GRAS by the World Health
Organization (WHO) and are approved for use in all the important alcoholic
beverage-producing countries. If fi ltration is part of the production process,
residues will most likely be undetectable, and even without fi ltration, if Good
Manufacturing Practice (GMP) is in force, residues will be minimal. All the same,
products that have been fi ned with gelatin or isinglass cannot be described as
'suitable for vegetarians' and those made using egg white or skimmed milk (or
equivalents) cannot be labelled 'suitable for vegans'.
Certain alcoholic beverages (e.g. some traditional wines and cask-conditioned
or bottle-conditioned beers) are fi ned but not fi ltered, and it is here that the use of
certain fi nings might leave allergenic proteins as residues, so that the product may
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