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Top-fermentation
brewing process
Belgium has a large variety of top-fermentation beers in the full range of density and
colour, flavour and aroma, with or without bottle conditioning: Spéciale Belges, amber
beers, Trappist beers, abbey beers, white beers, heavy blond, saisons.
Ingredients
Top-fermentation beers bear the signature flavour of the brewing water, selected malts,
unmalted wheat, rice or maize, hops, herbs and spices and yeast.
Brewing water
Unlike the extremely low mineral content of pilsner brewing water, brewing water for
top-fermentation beer is high in calcium, magnesium and their salts, sulphates and chlo-
rides.
Malts
These range from pale to amber or dark brown, coloured in the kiln or torrefied in the
drum (direct flame). It is mainly the malt grain that determines the basic flavour of top-
fermentation beers.
Unmalted wheat (up to 40% max)
For white beers.
Rice or maize
These do not contain any proteins and are used to reduce the protein concentration in
the malt, which is sometimes too high.
Sugar
To obtain heavy beers and a high degree of fermentation.
Hops
Bitter hopping:
for top-fermentation beers, high alpha, non-sour hop varieties added at
the start of the boiling process are mainly used to bitter the beer.
A selection of aroma hops are added at a later stage and ensure the desired aroma
profile:
Late hopping:
aroma hops are added at the end of the boiling process in order to pre-
vent the hop aroma from being lost due to evaporation as the brew is boiling.
Dry hopping:
extreme hop aromas are obtained by adding aroma hops after the fer-
mentation process, so that alcohol-soluble hop oils are also released.
Herbs: Bruges “gruut”
The use of hops became widespread in the 15th century. Before then, all beers were fla-
voured with herbs and spices. A blend of herbs and spices is known as a “gruut”. Herbs
contribute to the complexity of the flavour and aroma in hopped beers as well. Some
frequently used herbs and spices are bog myrtle, rosemary, coriander, juniper berry,
cinnamon, anis seed, cloves, sage and bay leaf. In Bruges, breweries were obliged to
purchase “gruut” from the city’s herbs and spices shop, known as the “Gruuthuse”.
Fermentation process
A yeast strain from the top-fermenting Saccharomyces Cerevisiae species, which are
active at high temperatures (ambient temperature from 15°C to 25°C), is selected by the
brewers of DE GOUDEN BOOM and used to ferment the brew.
Top-fermenting yeasts can be divided into two subspecies:
• non-phenolic: top-fermenting yeasts that are
exclusively fruity
and thus do not
give off a phenolic, smoked aroma
• phenolic: top-fermenting yeasts that give off a
smoked, phenolic aroma
compli-
mented by a more or less discernible fruitiness
DE GOUDEN BOOM, BRUGGE Tripel and STEENBRUGGE abbey beers are each
fermented with their own top-fermentation yeast strain, which gives them a phenolic,
smoked aroma.
Maturation
After the main fermentation, which takes 5 to 7 days, the brew is subjected to a warm
maturation phase (lagering) at approximately 20°C until the apple scent (acetaldehyde)
and the rancid butter odour (diacetyl) have disappeared. After this the brew is chilled to
0°C. The cool temperature helps to flocculate excess tannins and proteins (forming cold
turbid matter) and to precipitate the yeast, which further refines the flavour.
Acidity
pH 4.2.
Carbon dioxide content (CO
2
)
• At the end of the fermentation and lagering process: approximately 2.5 g CO
2
/l
• After chilling to 0°C, the beer is saturated with carbon dioxide gas up to:
approximately 4.7 g CO
2
/l for keg filling
approximately 5.7 g CO
2
/l for bottle filling
• With secondary fermentation in the bottle, the carbon dioxide content reaches
6 to 10 g CO
2
/l
04.2
DE GOUDEN BOOM BREWERY
TOP-FERMENTATION BREWING PROCESS
110
Masterclass
111