This is a complicated process, and I hope you give it some thought when you pop that next celebratory bubble of Champagne!
First, the Grapes …
The most popular grape varietals used for making Champagne are Chardonnay, Pinot Noir and Pinot Meunier.
Why so? The combination works extremely well together!
Chardonnay exhibits strong flavour on the palate initially, but dies back.
Pinot Meunier offers little initial flavour, but intensity increases on the middle palate as the Chardonnay dies back.
Propping them up along the way and building intensity with time is Pinot Noir – offering length and flavour persistence on the palate.
Selection criterion for grape ripeness varies between viticultural location, grape varietal and style of wine to be produced. But in general, you’d be looking for:
- high quality grapes which show some varietal flavours, without being over-ripe,
- sugar levels around 10-11 degrees Baumé, and
- balanced acidity with low pH to ensure freshness of the base wine.
Grapes are preferably hand-picked, and whole bunches pressed without crushing. This minimises colour bleed and tannin pick-up from the skins. As an added benefit, this decreases the need for sulphur dioxide use, so gives the winemaker the opportunity to use controlled oxidation techniques to introduce complexity in the wine.
The juice is settled and clarified – solids are racked off. If necessary further filtration -perhaps centrifuging – occurs.
Juice is fermented with use of selected yeast at between 11-14oC for 10 – 14 days. In France the addition of sugar is allowed to compensate for inadequate natural grape sugars. After fermentation, bentonite and diammonium phosphate are added for clarification purposes.
Assemblage & Coupage
At this point the wines are racked off and blended. This sometimes involves different grape varietals, even from different regions, to make the desired base wine.
Reserve wines can make up to 25% of the blend, and are used to add dimension and structure to the base wine. Reserves wines are often aged in oak barrels of different sizes to enable a variety of blending options.
The base wine is then fined using isinglass or gelatin and undergoes cold stabilisation.
Tirage Liquer is sugar syrup, which is added to the sugar at a level depending on the alcohol content required, prior to levurage [yeast addition], and tirage [bottling]. The bottles are crown sealed [metal cap] and stored.
The bottles are stacked laying horizontal for 6 months to several years depending on the quality of wine being produced, and maintained at a temperature of 12 to 15oC.
Yeast autolysis is not fully understood, however it is believed that it takes around 12 months for the yeast to impart sensory properties into the wine.
After the desired period of aging has passed, the bottles are stacked on shaking tables [riddling tables or pupitres], then inverted into racks.
For several weeks the bottles are individually twisted back and forth every day by hand.
The reason for all this agitation is to bring the yeast deposit to the neck of the bottle against the crown seal.
The necks of the bottles are chilled to minus 24oC, before the bottle is held right way up and the crown seal removed. The pressure inside the bottle blows out a plug of yeast and sediment. This can be done by hand or machine – obviously depending on size of production!
The bottles are then topped up [remplissage] with a mixture of expedition liquer [sugar dissolved in base wine] and the original wine. How sweet this liquer is depends on the style of wine being made.
Sometimes there is no liquer addition at all. Usually this is where richly fruit-driven styles are being made.
Bourbage & Habillage
The bottles are then corked [bourbage]. If an agglomerate cork is used, one or two high quality cork discs come in contact with the wine. A muselet [wire frame] holds the cork down against the pressure inside the bottle. Finally the cap is dressed [habillage] with foil over the muselet, and the bottle labelled.