Sparkling wine - the traditional method
OK - here is our brief explanation on the origin and making of sparkling wine.
Alcoholic fermentation produces carbon dioxide. In short, sparkling wine takes advantage of this by capturing the gas in the bottle.
There is some debate about who ‘invented’ sparkling wine. The classic story is that Dom Pérignon (a French Benedictine monk) chanced upon it and referred to ’drinking stars’, whereas the more prosaic version is that the English chemist Christopher Merret did it intentionally. But a bit of web research suggests the method was in use at least 150 years before them, so who knows.
Regardless, there is no doubt that the French advanced the production to an art form. They have also rightly claimed that the name Champagne be reserved only for sparkling wines made following a precise regime and using only grapes from the Champagne region. Fortunately there are no restrictions on us in using those methods.
First up, the grapes are picked less ripe than for still wine. A base wine is made in much the same way as a standard still wine – yeast is allowed to ferment (essentially eat) the sugar in the grape, resulting in the two main by-products – alcohol and carbon dioxide. When we’re talking about sparkling wine this is known as the primary fermentation and the carbon dioxide is vented away.
Once primary fermentation has ended the base wine is partially clarified and also cold stabilised to prevent tartrate crystal formation. The crystals (actually cream of tartar) are harmless but unsightly and in sparkling wine can cause extra problems.
The base wine is then bottled along with a little sugar, yeast, nutrients and other helpful stuff. The bottle is sealed with a crown seal very similar to a beer bottle cap – just a bit wider. The added yeast starts fermenting the added sugar and this time the gas cannot be vented as it is trapped inside the bottle. If the base wine alcohol is too high the secondary fermentation may not start or if it does, may not finish. Picking grapes that are less ripe means a lower sugar level hence less alcohol and more chance that the yeast in the secondary ferment can finish the job.
The secondary fermentation takes about 3-4 weeks although that varies depending on the temperature. There are a lot of facts & theories behind what constitutes the best conditions for the secondary ferment and what influences bubble size and other quality parameters. A search for ‘sparkling wine bubble size’ on the web will get you lots of information.
Now the bottle is then left undisturbed for an extended period - Champagne requires at least 15 months but longer is better and several years is not uncommon. During that period the yeast cells break down and more flavours develop.
When sufficient time has passed we move on to the next stage – riddling and disgorging.
Riddling is the process of moving the fermentation sediment to the cap region so it can be removed. The bottles are placed cap down in a rack and rotated a quarter turn twice daily. We do it manually because it’s not worth our while making mechanical gizmos for it. Although the bulk of the sediment falls down within the first few days it usually takes 3-6 weeks before the small amount stuck on the bottle sides makes its way to the cap. The ‘other stuff’ mentioned above includes bentonite – a clay emulsion that helps the sediment settle and compact.
The clearer the wine the better it is. If it is not perfectly clear, the bubble size will be bigger - important because small bubbles enhance the tactile sensation of the drink. This is why it’s important to cold stabilise the wine after the primary ferment. That minimises the chance of tartrate crystals forming in the bottle. Tartrate crystals are a good nucleating source for large bubble formation not so good for quality sparkling wine. There is some interesting bubble research going on in France which is worth a read. See for instance the article “Champagne physicist reveals the secrets of bubbly”.
Once we are satisfied that the wine is clear we freeze the bottle neck, turn the bottle right way up and remove the cap. Because the wine is under pressure it expels the plug of sediment. The wine may then have a small dose of sweetener added depending on the wine and its style. Some sparkling wines (though not ours) may also get a dash of wine and or brandy. The bottle is corked and the wire cage applied.
Theoretically the wine is ready for sale now. However, we have found that if the wine is left a while (say several months to a few years) the flavour and mouth feel can develop further. Fortunately this requires that we sample on a regular (but not frequent!!!) basis to monitor the progress.