The Flextank clamp manway (left) seals the vessel as securely as a barrel. Meanwhile, the screwed fitting in the manway (right) allows access to the container's contents in the same fashion as a barrel's bung closure.

Premium wineries are beginning to appreciate the utility of plastic tanks for various aspects of production. This article continues the discussion begun in "Advantages of Plastic" (Wines & Vines, January 2009). First, I'll review innovations that are occurring with plastic tanks, then I'll explore how wineries can reference these tanks in promotional information--as well as on the bottle.

There are valid and significant reasons for using stainless steel tanks in the wine industry, but plastic containers have some unique vessel properties that allow a winery to become more environmentally friendly and reduce its carbon footprint. They can also help winemakers make better wine--as long as they follow sound winemaking procedures.

The most important attributes of plastic are its flexibility and its relative strength. This flexibility allows plastic containers to hold liquids and to change volume based upon the thermal dynamics of the storage environment in a manner that is more similar to a barrel than a stainless steel tank. The rigidity of stainless steel and the thinness of the material used to make most stainless steel tanks for the wine industry do not allow manufacturers to seal the tank completely.

 

A cage by Schütz International Packaging (above) allows Flextank container stacking.

A stainless tank must allow for thermal expansion and minor releases of gasses that can come from microorganisms finishing primary or secondary fermentations, as well as some unwanted spoilage organisms that may be in the wine. If a wine is placed in a sanitized plastic container in the same manner as if it were going into an oak barrel and then sealed with a gasketed and clamped manway , and possibly a screwed bung closure, the wine will remain microbiologically stable until the container is opened. As explained in the January article, a stainless steel tank cannot provide this sanitary provision unless it is a pressure-tank type of container, and these tanks are not economically feasible for most wineries.

Plastic can structurally hold wine when relatively thin, but its lack of rigidity means that it needs an external support system. More plastic material can be used to create more rigidity, but then the plastic loses its advantage of flexibility. In order to maintain a reasonably stable shape, the plastic container must be supported by a frame. Schütz Industrial Packaging and Flextank each have designed frames that allow the tanks to stack one on top of another up to four to six high, depending on the manufacturer. Schütz has been around for many years, and its frames are in wide use.

 

Depending on the cage manufacturer, tanks can be stacked up to six high.

Flextank is a relatively new company, and its frames are not available on the secondary market as used frames. Fortunately, the Flextank plastic tank fits inside the Schütz frame. This allows users to save nearly $500 per tank when purchased with a used Schütz frame, and as a result, the used Schütz frame has become the defacto standard frame for this type of tank. The plastic container that comes with the Schütz frame is too thin and allows too much oxygen to be transmitted through the plastic into the wine, so at best it can serve as a temporary storage container. Like barrels, the stackable cubes can improve the gallons per square foot ratio. However, in order to access an interior cube, the stack must be broken down to get to the desired container.

A new way to organize

To provide framed plastic containers the same easy access as any tank or barrel in a winery, the framed plastic containers cannot be stacked, because there is not enough space to service the containers without breaking down the stack. The most logical approach, which would allow more space to service the containers, is to acquire pallet rack systems that will support the loads required by the Flextank Wine Cube.

Flextank has designed a non-stackable Wine Cube called a Pallet Wine Cube, which will fit onto commercially available pallet racks. The cubes then can be stacked as high as the pallet racks are rated. The benefit of this system for storage is that any container can be accessed at any time. They can be cleaned in place, and samples can be taken at any time.

 

A prototype of the Pallet Wine Cube (on the second tier in a pallet rack) shows access to the manway area. The design incorporates a standing area on the rear of the pallet.

The current version of Flextank's Wi ne Cube has a pocket on either side of the valve, which makes it somewhat difficult to remove the last half-liter of wine from the tank. A new design will be released this year adding a slope in that area to force the wine toward the valve. This new version of the wine cube will be released at the same time as the release of the non-stackable frame option. The non-stackable wine cube will have sufficient framework to keep the tank erect and safe, but will not hinder access to the manway, sample valve or bottom valve. Flextank has indicated it will sell the Wine Cube container as a separate piece, and will also have the non-stackable frame available on its website (flextank.biz) for purchase as a separate item. A price has been established only for the new bare Wine Cube container at this time. It will sell for slightly more than $600 without the frame.

Those readers who have the existing version of the regular Wine Cube may be interested in an experiment I conducted. I welded a piece of the same plastic from which the container is made into the pocket of the current tank. It definitely allows for complete emptying of the tank, with just the slightest elevation of the tank from the back.

Wine skins

Several years ago, Flextank developed the wine skin, a device that floats on the top of the wine in a partially filled tank, covering the entire surface area and touching the sidewall of the tank. This leaves only the smallest amount of wine in direct contact with the headspace in the tank. The Wine Skin is constructed of a urethane outer material with a foam insert.

The ease with which CO₂ crosses the urethane barrier is the one problem with the Wine Skin, and this is only a problem in wines undergoing malolactic fermentation or any other situation where CO₂ is released by the wine into the headspace. The skin has a relief plug to remove the CO₂.

With a Wine Skin in place, any fixed-volume tank is turned into a variable-capacity tank, with the further benefit that this device allows inert gassing of the headspace above the skin. The winemaker now has the best of all worlds in a tank: a variable fixed-volume tank with a protective inert atmosphere above it to minimize oxygen pickup (no more leaking tubes). This certainly will help to minimize the effect of the inflow/outflow of air into a standard stainless steel wine tank, and it makes even a partially filled plastic tank safer to store wine for a longer period of time.

Dexter series

 

A cooling coil (above in a wine cube) can be used to cold stabilize wines in all Flextank containers from 50 to 1,500 gallons.

The Dexter series of tanks is a new container system that will be released in March. The first in the series consists of four 80-gallon (300L) containers on a standard 48/48 skid, a size that will hold the results of 2 tons of fruit. These containers will strap together and can easily be moved about the winery by forklift. They also can be stored in the pallet rack system designed for the Pallet Wine Cube. They are small enough for one person to handle easily when empty. The lid is a standard Flextank clamping-manway lid that seals the tank in the same manner as the Pallet Wine Cube. Therefore, it can be used much like a standard oak barrel, with the ease of cleaning of the plastic tank. The tanks also are designed to have the controlled permeation that is Flextank's trademark feature. The Dexter series of tanks ultimately will include 50- and 60-gallon versions of the same containers. Each will have the clamping manway.

Cooling plastic wine barrels

Since Flextank is eliminating all screwed manways from its containers, every tank from 50 to 1,500 gallons will have clamped manways that truly seal the tank. In order to cool the wine in these containers for cold stabilization, a cooling coil can be lowered into the wine.

I tested the cooling coil (above right). In the 1,135L Wine Cube, this coil can drop the temperature to cold stabilization temperature in 24 hours. Using Foster quick connectors means that secure leak-free connections can be maintained, and the use of tubing and a box header give it the rigidity to withstand transfer from container to container. We use a forklift to insert it into the Wine Cube. This cooling coil costs about $2,000 to make and can be attached to fixed or portable glycol systems.

Conclusions

Between Flextank, Pasco Poly and Schütz, plastic tanks have entered the wine industry in a serious manner. Winemakers have found good and useful ways to incorporate these valuable tools into traditional winemaking. These two articles focused on the uses of smaller vessels, showing how and where they can be used in wineries producing a whole range of wine types. Still to be discussed are larger fermentation and storage tanks and tank systems, as well as a new winery design that incorporates plastic and stainless steel storage vessels.

I believe we are on the cusp of an evolution in winemaking that will provide another set of tools to help keep wine quality high and costs under control.

Can you call it a barrel?     In the course of this article, I have purposely framed my comments about these plastic containers by referring to them frequently as containers, because I think they should be thought of as barrels, not as tanks. It is common to refer to the blue drums used in wineries as barrels; in the beer industry, beer is stored in stainless barrels; in wineries, 300-gallon puncheons are referred to as large barrels.   A pla stic vessel, strictly speaking, meets the definition of a barrel. What constitutes a barrel in the wine industry? To me, a barrel is a container with a fixed volume that can be sealed by some device so that normal variations in ambient temperature do not affect the structural integrity of the container, and it is of a size that can be moved by forklift and stacked. I do not think that the construction material is part of the definition of a barrel. A container that meets these criteria should be called a barrel, and winemakers should be able to state that the wine stored in such containers is "aged in a barrel" (generically, when not otherwise modified). Wine stored in oak barrels is being stored in a specific kind of barrel. If the winemaker adds oak amendments to a plastic container, or barrel, then the wine is "aged with oak." With the wine industry growing, more and more oak is being used. Already French oak barrels are frightfully expensive and getting more so. The same is true for American oak barrels. We need more wineries to switch to using containers that will last for 20 or more years and that do not waste 75% to 80% of the oak wood to achieve the desired flavors in wine. We need containers that can be cleaned between uses, and that will preserve the wine in its proper condition. In this way we can have more of the needed oak at a price that will keep wine affordable. R.C.

Richard Carey, Ph.D., is president of Vitis Wine Center and winemaker for Tamanend Winery in Lancaster, Pa. He has written numerous articles on new technologies for the grape and wine industry as well as a series of articles on laboratory analyses in Wine East magazine. Please send your comments and questions about this article, as well as ideas for the basis of future articles, to Carey at rcarey@vitisresearch.com.