What’s sparkling wine?
Sparkling wine works by making still wine fizzy. Bubbles in the wine are formed by trapping carbon dioxide into a space under pressure, whereby half of the carbon dioxide is dissolved into the wine. In a sealed bottle of sparkling wine under a natural cork, the pressure can reach up to 6 atmospheres.
Yeast and sugar are added to a still wine before it is bottled (called tirage) to encourage a “second fermentation”. During this period, an equilibrium is created between the amount of carbon dioxide dissolved in the wine itself and the amount you find in the headspace, between the cork and the liquid.
When you pour the wine from the bottle, the carbon dioxide reduces to 1 atmosphere and escapes from the liquid through forming bubbles. The bubbles are formed in little pockets of dirt in your glass (usually from minute cloth hairs), causing a steady stream upwards from a selection of single points.
Finally, it’s worth noting that a good sparkling wine will take many hours to go flat. If you were to properly seal the sparkling wine after opening with a Champagne stopper and refrigerate it immediately you can slow down the process, making the sparkling wine drinkable for 1-2 days after opening.
Making sparkling wine in the traditional method: a step-by-step guide
1. Harvesting the grapes for sparkling wine
Often harvest for quality sparkling wines is done by hand to ensure all the berries used are healthy. Faults in sparkling wine tend to be more concentrated and noticed by consumers more easily, so care needs to be taken.
During harvest sparkling winemakers will pick in whole bunches as the stalks provide a natural drainage channel for the juice when it comes to pressing the wine. Drainage is important as it means less pressure can be applied, therefore minimising the level of phenolics extracted during the press.*
The bunches of grapes are put into shallow crates and sent off to the winery quickly to minimise air contact and avoid oxidisation. By packing in shallow crates it also means pressure is reduced when the crates are stacked, helping to protect the other grape bunches.
Sparkling wine grapes are picked at lower must weights when they are ripe but higher in acid. This is because sugar isn’t especially important for sparkling winemakers as sugar will be added during the tirage and dosage later to achieve the desired flavour.
The best sites for sparkling wine are cool climate (Champagne, Tasmania, Loire, England, etc.) and can produce ripe grapes with no “green flavours” but generally low in sugar and high in acids.
*Phenolics are generally found in the berry skins and include things like tannin, colour and bitter flavours – profiles often unwanted when you produce sparkling wine. In Champagne particularly they look for a clean juice as most of a Champagne’s flavour comes from maturing the juice on its lees.
2. Whole bunch pressing
As briefly mentioned above, the pressing of the grape bunches needs to be as delicate as possible to ensure that there is gentle extraction and minimum phenolics. This is especially key for Pinot Noir, Pinot Meunier and other red skinned grapes as they have higher phenolics; winemakers looking to produce a sparkling white wine will also want to avoid any extraction of colour as well.
Traditionally all Champagne was pressed in a large basket press using the grape bunch stems as natural drainage channels. The first free-run juice is used for the best quality sparkling wines (the stuff that comes off first). From a 4,000kg acre’s yield of grapes a maximum extraction of 2,550l of juice can be used for the production of Champagne, according to the AOC laws.
The first press is called the “cuvee” and often regarded as the finer juice. The second pressing is called the “tailles” (or tails) and considered of lesser quality. Each pressing process can take 3-4 hours depending on the size of the press.
The maximum yield permitted for sparkling wine made in the traditional method in France is in the production of Crémant d’Alsace, which allows up to 80hl/hectare to be harvested. A winemaker here can extract 100 litres of must from every 150kg of grapes.
Cava and many English sparkling wine producers use either the basket press or a modern pneumatic press to extract the juice. Freixenet, a large Cava producer, called the pneumatic press the “gentlest of all presses”.
3. First ferment
Often this process is quick and warm. If a winemaker chooses to ferment the still wine too cool it can result in undesirable noes of banana and pear drops. Instead they look for a clean juice. Stainless steel is the common vessel for the first ferment in the traditional method although some producers still use oak.
Malolactic fermentation, whereby the malic acids (think bitter apples) are turned into milky lactic acids to soften the wine, is sometimes undertaken. Malolactic fermentation reduces the acidity in a wine as well, which may be desired.
Once the first ferment is complete you then have the base wine, a still wine that is high in acid and usually clean in flavour. Base wines may be maured in stainless steel or oak vessel, varying producer to producer.
This is a very highly regarded skill! The craft of blending is the secret behind the world’s greatest sparkling wines. While many great single varietal styles are produced, such as 100% Chardonnay Blanc de Blancs, most iconic Champagnes or high quality sparkling wines are Cuvées (or Blends).
Numerous base wines will be blended together to achieve a House flavour – or, in Vintage years, a distinct flavour to reflect the style of the year. On a basic level these base wines will be from different vineyards and grape varieties. However, in more complex styles, base wines are often mixed with other base wines tha have been matured or with reserve base wines from previous vintages. This is very common when producing an “NV” (Non-Vintage) style.
The challenge with blending is to predict the flavour of the blend once it will have gone through a second fermentation and the process of ageing on its lees, which most traditional method sparkling wines are required to do under their respective laws.
5. Bottling and tirage
Tirage refers to the addition of sugar, yeast and yeast nutrients to a bottle of blended base wines to encourage a second fermentation.
Specific strains of inoculated yeast are often used for both fermentations as these minimise off-aromas and are more reliable to achieve a consistent result. It’s also important as the yeast needs to be able to function under the production of sulphur dioxide and at low temperatures and a low pH typical of second fermentation.
The sugar can be from cane or grape but is usually mixed into a base wine solution to be added to the blend. Generally a tirage of 24g/litre of sucrose is added for second fermentation to be possible.
At this stage the bottles are sealed under a crown cap and stored on their side. Riddling agents may also be used to help clump together the lees (dead yeast cells) produced during second fermentation, making it easier to extract the lees at dosage later on.
6. Second fermentation
The most important thing to remember about the traditional method is that second fermentation happens in the bottle. This process is slow, often lasting up to 8 weeks, and conducted at around 10C. The CO2 produced, as in any fermentation, is trapped in the bottle where half dissolves into the wine and the other half is released in equilibrium to the headspace.
Second fermentation leads to a pressure in the bottle of between 5-6 atmospheres (the minimum for quality sparkling wine under EU law is 3.5 atmospheres, with lightly sparkling defined as at least 1.5 atmospheres). The alcohol level is usually at 12-13% ABV at this stage. The alcohol in Champagne has risen on average by around 0.8% in the last decade due to the effects of climate change.
7. Lees ageing
Once second fermentation is complete the wine is left to age on its lees for a minimum of 9 months for most quality sparkling wines. All Champagne must be left to mature in the bottle for at least 15 months, of which 12 months must be matured on its lees. However, most Champagne producers will leave sparkling wine on its lees for at least 18 months and the best for many years. Vintage cuvees must be ages in bottle for at least 3 years.
The effect of lees ageing is to create an autolytic character
This is where a bottle of sparkling wine is gradually turned sur pointe (upside down) so there is a gentle movement of the lees to the neck of the bottle. If it were done suddenly, the lees would end up suspended in the liquid. This process used to be done by hand and took as long as 6 weeks to complete. Today a mechanism called the gyropalette completes the process over just 3 days. See video below.
Disgorging is generally done mechanically for speed but it used to be a very skilled practice by hand, albeit a dangerous one. The bottle neck, where the lees have been riddled to, is frozen in a brine solution creating a plug in the neck of the bottle of yeast and ice.
The crown cap is then removed and the ice plug shoots out the top of the bottle, removing the yeast and leaving the sparkling wine. As this is done under pressure, some of the wine is also removed in the process.
10. Topping up and dosage
Also called the Liquer d’expedition. This is the final addition of sugar syrup that determines the wine’s sweetness and style. The dosage is made up of wine and sugar. Sometimes it may also include a small amount of red wine to change the colour of the final sparkling wine, a process permitted in Champagne (although not the rest of France).
Styles of sweetness in sparkling wine as classified by the EU:
0 – 3 g/litre > Brut Nature or Zero Dosage (no sugar can be added at dosage at all)
0 – 6 g/litre > Extra Brut
0 – 12 g/litre > Brut (the most popular style in the UK)
12 – 17 g/litre > Extra Sec or Extra Dry (confusingly sweeter than Brut)
17 – 32 g/litre > Sec, Secco or Dry
32 – 50 g/litre > Demi-Sec or Medium Dry
50 g/litre + > Doux, Dulce or Sweet
11. Ageing and release
Finally the wine is aged in bottle to allow all of the flavours in the wine to integrate and for the final wine to achieve balance. The very best vintage sparkling wines might be matured for decades or longer.