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Spontaneous fermentation
brewing process
Brewing water
The brewing water has a rather high mineral content.
Lambic malt is prepared in the malt factory under the lambic brewer’s strict process
40% of the starch is from unmalted wheat.
Sour and bitter tastes do not go well together! Nevertheless, hops are necessary be-
cause of their bacteriostatic properties and to curb the growth of bacteria. This is why
hops over a year old are used; they have lost their bittering, but not their bacteriostatic,
The brewing process
The brewing process follows the “turbid wort method”, in which hot water is added
to the mash in order to achieve the higher temperature required for converting starches
to sugars.
The first draught or the first concentrated extract leaving the lauter tun also has a very
high protein concentration. This first draught is boiled separately (for 3 hours) in order
to let the proteins coagulate as much as possible, following which they can be removed
through decanting. Excessive protein concentration encourages the development of
acetic acid bacteria, which should be avoided. The second draught is added to the
clarified first extract and, after adding hops over a year old, the entire mixture undergoes
sustained boiling (more than 3 hours).
Spontaneous fermentation process and maturation
in oak casks
As the brew is cooled down in the “open coolship”, it is spontaneously inoculated with
the microflora from the ambient air (wild yeasts, lactic acid bacteria, Brettanomyces
Lambicus and Bruxellensis).After this it first undergoes main fermentation and then long-
term maturation in oak casks (for at least two summers). In order to prevent excessive
development of acetic acid bacteria, beer is only brewed from October to April, when
the ambient temperature is below 15°C. During maturation the organic acids which are
formed are converted into fruity esters. Almost all residual sugars are eliminated due to
the action of the Brettanomyces.
pH 3.2 to 3.6
Variants and their carbon dioxide content
The beer is given the name “lambic” at the end of the maturation process; it then has a
carbon dioxide content of 0.5 CO
/l to 2.0 g CO
/l (flat beer).
If lambic is given additional fermentation in the bottle, it will bears the name “geuze”
(sparkling lambic), otherwise known as Brussels Champagne. The carbon dioxide con-
tent rises up to 6 g CO
/l to 10 g CO
Fruit varieties of geuze
Maceration of lambic with fruit, such as small wild cherries or raspberries, is the tra-
ditional method of producing high-quality fruit beer. Cheaper imitations are a blend of
lambic (or another beer) with fruit juice, fruit extracts or flavourings.
Old geuze
The designations “old lambic”, “old kriek” and “old geuze” are protected in Europe
(Guaranteed Traditional Speciality, GTS) and stand for authentic traditional lambic, kriek
and geuze beers brewed using 100% spontaneous fermentation and having a weighted
average of one year’s maturation in oak casks.
Non-traditional geuze
Under a Belgian law as amended in 1993, geuze must be made based on spontaneous
fermentation only, without specifying what percentage of spontaneous-fermentation
beer must be present. Hence, geuze beers and their fruit varieties that are not prefixed
with “old” are not produced by spontaneous fermentation alone, or in some cases only
to a very limited extent. If you want an authentic traditional geuze, then make sure it
bears the prefix “old”.
Spontaneous fermentation