Cognac

The grape vines employed for the base wine for cognac production are nearly all from Charente and the adjacent regions of Deux-Sèvres and Dordogne. Furthermore, the grape varieties must be either Ugni blanc, Colmbard or Folle Blanc, with the exception that up to 10% can be wines from Jurançon blanc, Semillon, Montils, Blanc ramé or Select.

Ugni blanc is by far the major variety, affording wine high in acidity and relatively low in alcohol which renders it most suitable for distillation. The reader is referred to Cantagrel and Galy (2003) for details of the wine making intricacies. But suffice to say here that the microflora employed for fermentation is endogenous, with one report suggesting that more than 650 yeasts are involved. The belief is that active dry yeast (ADY) leads to the production of inferior products. Sulphur dioxide is not employed. Fermentation is relatively fast, the wines being maintained on the lees and subjected to malo-lactic fermentation. The sooner the distillation after fermentation, the better the quality of the product as there is less development of ethyl butyrate and acrolein (from the decomposition of glycerol, see Chapter 5).

The distillation employed in the production of cognac is known as the Charente process. The still must have a capacity of less than 30 hL, which means that the maximum practical working volume is no more than 25 hL. The vessel must be heated by an open fire.

Two successive distillations yield a spirit of <72% ABV. In the first stage, 27-30% ABV is achieved. In the further distillation of this, three major fractions are generated: the heads, the heart (spirit cut) and the seconds. The heads, comprising 1-2% of the total, contain the most volatile components and are considered detrimental. The most 'noble' components are in the heart and herein is the cognac spirit to be matured. The seconds are recycled.

The nature of the wood employed for ageing of cognac has great significance. The fineness of the grain impacts the extent to which phenolics and other tannins are extracted, as does the shape and size of the barrel made from that wood and the extent to which the wood is charred in the shaping process. The wood is generally dried in the open air for over 3 years. New spirit is introduced to this new wood for a period of 8-12 months before transferring

Table 6.2 Changes in volatiles in cognac during different periods of ageing in wood.

Concentration (mgL 1)

Table 6.2 Changes in volatiles in cognac during different periods of ageing in wood.

Concentration (mgL 1)

Component

0.7 years

5 years

13 years

Coniferaldehyde

3.7

5.9

6.7

Gallic acid

4.6

9.0

15.3

Sinapaldehyde

9.5

17.8

17.0

Syringaldehyde

2.3

8.9

17.6

Syringic acid

0.6

2.6

7.0

Vanillic acid

0.3

1.4

2.8

Vanillin

0.9

4.4

8.8

Derived from Cantagrel (2003).

Derived from Cantagrel (2003).

to older barrels, thereby avoiding the pick up and development of excessive astringent and bitter characteristics. Oxygen enters through the stave and is used by enzymes contributed by moulds in reactions that have a role in the ageing process. There is also volatile loss through the stave. The changes in key wood-derived volatiles that result from different periods of ageing are depicted in Table 6.2.

Several batches will be blended during ageing. New distillates at 70% ABV are lowered in successive stages to the 40% ABV level at which the product is bottled.

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