Wine Tanks
Materials Used for Wine Tanks
One of the most important decisions that a winemaker needs to make is what type of material for the tank. These days, the most popular types of material used for tanks are made of stainless steel, wood, concrete, and plastic.
Stainless Steel
Stainless-steel tanks can be constructed to hold very large volumes and can be temperature controlled, and the stainless steel does not react with the wine, making it practical for any size of winery. Tanks come in a variety of sizes ranging from a few hundred gallons to huge tanks with capacities of hundreds of thousands of gallons. It is easy to make stainless-steel tanks in whatever dimension is required, especially for red wines where a large diameterto- height ratio to obtain thin caps is required.
Grades
The two most common grades of stainless steel used in winery equipment are the 304 and 316 grades. The difference between the two is that 316-grade stainless has slightly more nickel than 304-grade and it also has a small amount (2%) of molybdenum in the alloy. Grade 304 is cheaper than grade 316, because it contains less nickel.
Stainless-Steel Surface Finishes
Stainless steel is usually smooth and slightly reflective, but in some instances, their surfaces are grainy or are brushed in one direction. These varying profiles are called surface finishes. An important characteristic of surface finish is surface roughness. This is the deviation of microscopic peaks and troughs from the ideal surface of a metal. The type of surface finish and the surface roughness are important specifications for stainless steel tanks since it affects moisture retention and material adhesion on the tank's surface.
Concrete
Although winemakers in Europe have been utilizing concrete to make wine for centuries, winemakers in the United States are beginning to once again appreciate the concrete tanks (Figure 22.5). Concrete can be cast in a wide variety of shapes. This has led to some creative tank geometries, ranging from neo-amphorae, to egg-shaped tanks, to tanks that look like they have been recycled from the Russian space program. The shape also helps to keep the cap continuously submerged. Concrete is made from crushed stone, rock and sand held together by cement. The cement is only about 15 percent of the total mass of concrete. Concrete is stronger and less porous than cement alone. Concrete tanks can either be unlined, fiber-glass lined, or epoxy lined. The accessories that are required for concrete tanks such as valves, pipelines, connections, manholes, etc., are made from stainless steel to avoid metallic migrations and dirt.
Egg-Shaped Tanks
One of the latest trends in winemaking equipment is the egg-shaped wine tanks that have found their way into many wineries (Figure 22.5). Some winemakers prefer egg-shaped tanks because of the effects in the maceration process during fermentation. Mention is often made of a homogenous ferment, producing a complete and complex wine, with more concentrated primary and secondary flavors, without masking or changing primary fruit flavors.
Wood
After almost disappearing from the U.S. wine industry, wood tanks, especially wooden fermentors, have seen something of a renaissance in recent years (Figure 22.6). The tanks (open top) and the tanks (closed top) of varying capacity ranging from 1,000 gallons (38hL) and more are also used as fermentors. They are generally made of redwood or oak.
Plastic
High-density polyethylene (HDPE) food grade safe plastic tanks are increasingly being used by winemakers for harvesting, fermentation, and maturation among other uses as an economic alternative to stainless steel and oak barrels (Figure 22.7). There are numerous reasons why specialized plastic tanks are attractive to the wine industry. The use of HDPE tanks, alone or in combination with oak alternatives are regarded as potential inexpensive alternatives to barrel ageing. According to the manufacturers of permeable HDPE tanks, the tanks can be manufactured with controlled permeability levels to oxygen, providing an alternative way of oxygen incorporation into wines.
Click on the following topics for more information on wine tanks.
