The differing contributions of fermentation decisions

Wine Folly: Eggs create an internal flow with thermodynamics.

Wine quality and style are determined by several key factors including farming philosophy, vineyard management, vintage conditions, quality of fruit at harvest and winemaking. The winemaking part sounds simple, but is in fact the product of many hundreds of decisions made by winemakers throughout a vintage. Fermentation decisions including choice of vessel, size and shape, what it is made from and length of time an emerging wine spends inside a container for ageing all contribute to style, complexity and quality.

Fermentation is a an immediate reaction between wine yeasts and the simple liquid sugars of glucose and fructose released from crushed grape berries. The yeast itself can be from the skin of the grape or introduced as a particular strain. Used on its own the yeast from the skin of grapes causes a natural or wild ferment reaction producing aroma and flavour esters that can add texture and complexity in wine often reflecting the environment they originate from. Some winemakers use a pied-de-cuve method using wild yeast to start a ferment in the vineyard first before transferring the must into the winery. The size, shape and material of the containers used to ferment wine is critical to the outcomes of quality and style.

Steel

Stainless steel tanks are a common and modern vessel for fermentation. The size and number required depend on the capacity and needs of a winery. They range in size from 250 to 150,000 litre, sometimes bigger, ensuring volume wine production and uniformity of style is easily achieved through large capacity tanks. Steel tanks of this kind typically include heating and cooling coils to control fermentation cycle. If a wine is expected to have an oak influence the juice can be transferred to wine barrels for ageing and this is the more common practice in New Zealand. Alternatively, large planks of oak can be suspended inside a steel tank adding wood flavour. Oak chips or varying sizes and toast levels can also be used.

Wood

Wine barrels are very common for fermenting and ageing wine and range in size from 50 litre upwards. The most common you’ll encounter in a winery are 226 litre Bordeaux barrels, 228 litre Burgundy barrels, 500 litre Puncheons, 600 litre Demi-Muids and 900-1000 litre Fuders. There are even Cigares or cigar shaped barrels or straight sided shapes starting at 2000 litres capacity. So long as they are kept water tight barrels can be used for fermenting, storing and ageing wine. Oak is the favoured wood for barrels with French, American, Hungarian and Slavonian commonly used. Barrels provide a unique environment for wine allowing mico-oxygenation to take place by letting tiny amounts of air through the sides of the barrel into the wine over an extended period of time. If the inside of the barrel is toasted (charred by fire) then the flavour of the toast is absorbed into the wine as well.  Brown spices, raw sugar, coconut and sweet raw wood aromas and flavours can be discovered in a wine using barrels. The intensity of wood or toasted wood flavours decreases each time a barrel is used to a point where no wood or toast flavour remains – this is called neutral oak. A barrel can always be used for micro-oxygenation which in turn builds complexity into wine.   A barrel can also be used to keep the spent yeast, called lees, to add complexity and texture. Stirring the lees, or not, determines the impact. The larger the barrel the less surface to juice ratio yet no matter the size they all contribute to the flavour and texture of a finished wine. Though not common in New Zealand it is possible to suspend strings of new oak wood pieces inside a neutral barrel allowing wood flavours to be included.

Earth

The use of eggs or egg-shaped containers to ferment and age wine is becoming more common in New Zealand. Qvevri, Amphora, Tinaja or egg-shaped earthenware containers can be traced back to Georgia, Roman times and early Spain several thousand years ago. Understanding how these containers contribute to the flavour and texture of wine back then is unknown, but they were the common vessel for storing wine often buried in earth underground or near the surface in cool areas. One modern version of the amphora are eggs made from a special type of clay, concrete, wood or steel. Only two wooden egg-shaped barrels are in New Zealand with an increasing number made of concrete. These vessels are not about oxygen or material flavour ingress into wine, like barrels, but the use of natural and very minute convection currents caused by yeast and the heat of fermentation in a near anerobic environment, developing texture and flavour synergies. The use of and integration synergies between grape skin, juice, whole bunch grapes, yeast and the forces of container environment deliver wines of enormous complexity with each contributing component decided by the winemaker. Eggs and Qvevri containers produce individual wines with each new vintage delivering something special to be discovered.

Plastic

Fermentation containers made of plastic are more common than you might think. Their light weight makes them easy to move around a vineyard or winery, can be covered or left open-top. Standing alongside using a ladder or platform makes is easy for piegage (pushing the cap of floating skins back into the juice during fermentation) or remontage (pumping the juice from the bottom of the vessel back over the top of the skins). They are vessels of convenience not show and assist in winemaking efficiencies for red or white wines.

Glass

No longer common at commercial wineries glass containers for fermentation allows for the winemaker to observe the activity of yeast and juice reactions up close. Anerobic except for the opening at the top these vessels they are typical for small batch or experimental wine making. Glass is also very heavy when filled with liquid wine and present quite a few safety challenges in a busy winery, and for home use, they have by in large disappeared from use in New Zealand. I use a small car-boy to make bulk Negroni!

Concrete

If your travels take you to Burgundy one day soon then you may discover some producers there still ferment wine in concrete. It can look like a row of cubed swimming pools in a winery, concrete tanks were once the norm for many producers to ferment juice from multiple vineyards before transferring to wood for ageing. Once-upon-a-time New Zealand wine producers also used concrete tanks for fermentation before wood and steel allowed for more controlled wine making. They were cheap to make, the size was determined by the producer and was a convenient way to start a winery. One of the issues with large concrete tanks today is safety and hygiene. The only evidence that remains of concrete tanks I have encountered are at Pleasant Valley Wines in West Auckland. Even here they are no longer used and may be viewed if you’re curious.

The back label on a bottle of wine can reveal the fermentation vessel though most do not. The best way to find out is ask the front of house team in your favourite liquor store or restaurant. You can always use the internet to download the technical information about a wine from the producers’ website or send them an email.