The maturing of wine calls upon ancestral know-how and methods, but also on the most up-to-date techniques and materials. From vine to glass, and including the subtle stages of wine-making, stainless steel plays an important part in every stage of the process.
Grapes are gently removed from the vines with the traditional method of hand harvesting. The stainless steel blades of the secateurs skillfully grasp the grape clusters through the dense leaves around the branch tendrils and remove them from the vine. It’s a labour of love, and a very expensive process.
Today many vintners are opting for special machines which straddle the plants, shaking the vegetation with threshers causing the grapes to fall into a recovery mechanism combined with an embedded sorting system that removes the leaves.
To avoid any corrosion of the equipment and preserve the integrity of the grape, all the parts in contact with the clusters; connecting rods, power transmission chains, threshers, buckets and receiving plates, are made of Type 304L (UNS S30403) stainless steel.
Crushing, pressing and fermentation
Once collected, the harvest is immediately routed to the winery to limit oxidation and optimize wine-making conditions. In the
winery, the clusters are placed in a rotating cylinder for stripping in order to remove the grapes from their “skeleton”, or stalk.
At this stage, the grapes for red wines and white wines take different paths.
For the reds, once destemmed, the grapes enter the pressing process, followed by the maceration step in stainless steel vats that place their juice (must) into close contact with the solid particles: skin, pulp and seeds. This process can last several weeks while fermentation occurs and the solid parts—skins and seeds—agglutinate in grape-cake. The grape-cake is removed from the vat and pressed to extract the “press wine” which is returned to the vat for a second fermentation.
For white wines, the harvest is rapidly stripped and the grapes are poured into a metal hopper and pass between rollers that will burst them to extract their must but without crushing the pulp or breaking the seeds that could release their components. When the must deposit is removed, alcoholic fermentation transforms the sugars into ethanol by the action of yeasts, in clear juices free of skins and solid particles. This takes place in stainless steel vats featuring integrated thermal regulation systems. It lasts from a few hours (sweet white wines) to several days (dry white wines) depending on the type of wine sought.
For both red and white wines, several steps of racking and must settling allow the wine to be separated from its lees (residual yeast) and other scale producing residues that deposit at the bottom of the vat during fermentation. The addition of sulfites (sulfur dioxide/SO2) protects the wine from oxidation and prevents the formation of fungi and molds. These stages involve transferring the wine from one vat to another. Ease of cleaning the stainless steel vats is essential for time and labour savings and to ensure that unwanted microorganisms are not present to spoil or alter the taste of the final product.
Blending and bottling
The blending of several grape varieties, with complementary qualities, can then take place in the vats in order to obtain the best vintages.
Before bottling, the wine passes through plate filters, earth filters, or better yet, mesh or ball filters made of Type 316L (S31603) stainless steel that capture the last impurities without altering the taste of the wine or releasing polluting waste.
The stainless vat advantage
While wood continues to be a legacy material of choice for vats in the most prestigious wineries, its use remains for the most part artisanal. It requires great care, is sensitive to microbial contamination, is a poor conductor of heat and provides an imperfect seal.
The advantage of concrete casks is their airtightness and good thermal inertia. But they are hard to clean as the acidity of the wine attacks the walls and the built-in construction makes any subsequent fit-out of the cellar complicated.
For these reasons, stainless steel has seriously come into play, with clear advantages in the installation, operation and maintenance of a high-performance fermenting room.
Wine-making vats, vats for storing red wine and temporary vats for white wines are primarily made of Type 304L stainless steel. This grade is ideal for moderately aggressive environments and containers not intended for long-term storage.
The addition of molybdenum for improved resistance to corrosion makes Type 316L stainless steel well-suited to white wines whose fermentation must be highly controlled. In particular, it is used for sweet wines that are more aggressive due to the addition of sulfur. Type 316L is also suitable for rosés, alcohols and fortified wines.
Tailor-made vats, manufacturing flexibility and the ease with which nickel-containing stainless steel adapts to these technically advanced designs has enabled the production of truly spectacular wine cellars.
Playing a key role in every stage of the process, it’s clear that stainless steel and wine-making will continue to be a successful blend for vintners in the years ahead.