April 2017 Issue of Wines & Vines

Benefits of Egg-Shaped Wine Tanks

Winery trial compares half-ton bins and plastic eggs

by Richard Carey

One of the latest trends in winemaking equipment involves the egg-shaped wine tanks that have found their way into many wineries. There is a great deal of myth surrounding the utility and functionality of these vessels. Since I used an egg tank last harvest, I decided to review the literature about how these tanks are being used and what a winemaker might expect if venturing into this “new” esoteric method of wine production. 

I have been making wine for nearly 40 years, but when I first started, the last of the early 20th-century concrete behemoths had been retired. Because those old tanks were then described as a dirty and old method for wine production, I have been fascinated by the new interest in the use of concrete as a tank material and by its use specifically in an egg shape.

As a construction material, concrete is useful in the winemaking process. There are many hundreds (if not thousands) of wineries in Europe that would not exist if it were not for row upon row of concrete tanks. These tanks, however, are not egg-shaped or treated in the same way. They are generally epoxy lined and fill the winery from floor to ceiling. Many of these tanks were built decades ago and are still producing some very fine wines. From a financial standpoint, those tanks provide the least expensive cost/volume/unit area over time.

The egg shape is not entirely new. The amphorae of Greek and Roman times were a precursor to this shape—they were eggs with a midriff bulge. Even today, in Georgia and parts of Italy, wineries are using qvevri (very large terracotta amphora-like tanks that are buried in the ground) to produce wines that are unique in color, interesting in taste and quite delightful.

Several companies in Italy are now producing terracotta tanks made in the old style, with modern attachments such as manway-like lids, valves and support structures to enable them to be moved. iPak Wine and the Vintner’s Vault are two companies that are importing terracotta tanks to the United States. 

Six years ago, shortly after the egg shape started to make inroads in wine production, an egg-shaped tank made of oak was designed and produced by artisan Joseph François and exhibited at the 2011 SIMEI trade show in Milan. (See “Egg-Shaped Wine Tanks Whet Appetite” at winesandvines.com.) At about $28,600 and 1,000 liters, the egg-shaped oak tank is undoubtedly one of the most expensive tanks on a per-liter basis that has ever been produced.  

Today, however, the egg-shaped tank is usually constructed of concrete. In this new iteration, concrete as a tank material is offering alternatives for how wine can be made without oak. These tanks are “naked,” meaning that the tanks do not have any coatings on the inside surface.

New techniques are being developed for the construction of these tanks by companies such as Sonoma Cast Stone. These techniques include some complex accessories and provide additional utility to these tanks. Sonoma Cast Stone and another company, Vital Vessels, are both pushing the envelope in design and functionality.

According to Steve Rosenblatt, president of Sonoma Cast Stone, the company is in the last stages of patenting a new tank-construction process. The patent will secure the company’s current innovations in tank design, add greater control over the final wine contact surface and provide more longevity to the tanks. In addition, the patent will include the company’s development of new concrete materials. In Rosenblatt’s view, the new materials will offer greater ability to clean the tanks and leave less potential for any interaction (especially at first) of residual Portland cement with the wine.

In concrete tanks, the Portland cement moves to the surface during curing of the concrete. As of now, before any concrete egg is used for wine, the tank’s inside surface must be washed with an aqueous solution of 12% tartaric acid to remove residual Portland cement. After that process, winemakers using these tanks should not scrub the inside surface or use hot water to wash the tanks. Hot water could crack a tank due to the unequal expansion of any stainless steel fittings such as manways and/or valve inserts. Scrubbing the surface could eventually mar and/or gradually roughen and remove it. 

The construction of an egg tank is a process similar to constructing a swimming pool. Flowable concrete, embedded with fiberglass and other materials, creates the structural outside of the tank. Next, Sonoma Cast Stone adds PEX tubing to the inside surface. The tubing will be used for their glycol chilling system that is embedded in this layer of the concrete wall of the tank. Once that process is finished, the final layer of very fine-grained materials is formed against a highly polished mold facing the tank’s interior. Once cured, the mold form is removed, leaving a smooth production finish. The Sonoma Cast Stone tanks start at about 1,600 liters, and the cost is approximately twice that of stainless steel tanks of equivalent size.

Vital Vessels in Carmel, Calif., is another high-tech company making egg-shaped tanks—in this case using ceramic materials. The manufacturer’s concept is based on the permeability of the ceramic material to the liquid in the tank. The company’s literature describes a process of evaporative cooling that cools the surface of the tank, which then transmits that energy to the wine in the tank. As wine cools, it becomes more dense and slowly sinks to the bottom of the tank. Through the process of the cooled wine sinking to the bottom of the tank, the wine at the center of the tank, which is slightly warmer, rises to the top. The egg-shape, having no sharp angles on its inside surface, translates the upward movement of the wine to a cascade down the outer shell, where the wine is cooled by the shell surface. With this movement, caused by the temperature differential, the two areas of the tank mix continually and gently.

This dynamic is not necessarily happening in standard concrete tanks, since the walls of those tanks, while porous, are much too thick to cause the slight temperature effects of the thinner, ceramic-walled vessels. However, one could make the argument that the Sonoma Cast Stone glycol system might impart that same effect.

The Vital Vessels tanks are a maximum of 675 liters and, since they are made of ceramic materials, they are quite different from concrete tanks. For example, the wall thickness is measured in millimeters (the walls are 9 to 12 mm thick), not multiple inches of material. Since the tanks are ceramic, they could be subject to cracking due to shock. To guard against that possibility, each tank is fitted with stands with insulating padding for protection; there are polymer pads between the tank and the stand, and the stand and the floor. Vital Vessels makes smaller tanks (down to 43 liters) that are used for water and other beverages. The company says that these tanks are fired in one of the largest ceramic kilns anywhere and take 42 hours to fire.

There are other small tanks being produced from concrete that are not egg-shaped. Vino Vessel in Paso Robles, Calif., has created a line of concrete tanks and a concrete barrel. In addition to its egg-shaped tanks, Sonoma Cast Stone has just designed a four-barrel tank that is squat and chest-like; it can be stacked two high.

The benefits (and problems) of concrete tanks
Many wineries are now using the concrete egg-shaped tanks. When installed, these tanks may be gorgeous pieces that are impressive in size and shape. But is their utility based on the egg shape, or is it because they are constructed with concrete? Are these tanks going to become the next new standard in winemaking? Are there other materials that will provide the benefits without the very real obstacles presented by concrete tanks?

The first benefit of concrete is its mass, which also is its first negative aspect. The mass of concrete provides one of the important requirements for good winemaking, which is long, slow changes in temperature. But because of the tank’s weight, a winery shouldn’t plan on moving it very often.

One major concern is that after use, cleaning concrete needs to be done carefully. As indicated above, hot water is not recommended, especially if there are any metal parts imbedded or attached to the tanks. The tank can crack if too great a temperature difference occurs between metal and concrete. Aggressive cleaning measures such as power washers or high-intensity nozzle-cleaning balls cannot be used. Even strong bristled brushes can create problems on tank surfaces. Instead, alkaline cleaners such as peroxycarbonate are frequently used.

Concrete egg tanks are probably best suited for wines whose style excludes contact with oak and for those that would benefit from micro-oxygenation. Wines requiring no oxygenation usually are stored in stainless steel. After storage in stainless steel, the fruit is brighter and more true to that naturally expressed by the wine. Some have described that impression as less complex, but I don’t agree with that assessment. If a wine is expressing only a single fruit note such as pear or apple, that is an example of a simple wine.

Grape wines, unlike other fruit wines, are not by nature single-note wines. When made well, there may be an emphasis on one note above another, but in general they have many complex layers of fruit components expressed in any one wine. A winemaker mixes these notes and builds complexity. The aging process changes the fruit to more oxidative components, which alters the wine’s style. So choosing concrete not only adds the oxidative component but the surface material may give a stony impression from the concrete. In other words, the tank provides another tool to get to the winemaker’s stylistic goal.

What other materials can be used for tank construction if the goal is a wine produced in a barrel-like experience without oak contact? A winemaker cannot be sure there will be no wood flavor imparted even in neutral barrels because, in most cases, these barrels have some wood flavors, just less than needed for traditionally oaked wines.

One alternative is a plastic tank produced by Flextank USA to allow micro-oxygenation through the plastic. About five years ago, the company designed an 850-liter egg-shaped tank called the Apollo that had the oxygen transport of an oak barrel, an 18-inch manway and valves at the bottom. The goal was to offer an alternative to fermentation in MacroBins, but without the impediments of concrete. The Apollo eggs are light, have a smooth inside surface, can be sanitized with just about any material commonly used in wineries and are a fraction of the cost of other egg-shaped tanks. The downside is they don’t have the visual appeal of the more massive concrete tanks or sleek ceramic ones.

Comparing fermentation in MacroBins vs. the Apollo egg
During the 2016 harvest I had the opportunity to compare the fermentation of Chambourcin grapes in two short (half-ton) MacroBins, one insulated and one not insulated, and in an Apollo egg. MacroBins are routinely used for fermentation of small lots of about 1 ton or less. Egg-shaped tanks have been proven to provide a superior fermentation regimen compared to several other methods with little or no extra work or equipment needed.

I ran side-by-side fermentations of the same amount of fruit in the two MacroBins and the Apollo tank. The uninsulated MacroBin fermented substantially cooler (8° to 9° F lower) than the insulated bin. The Apollo tank was intermediate to the two bins, and because of that temperature difference, it gave the best fermentation. The cap temperature was 4° to 5° F lower than the insulated tank, and the juice temperature was 3° to 4° F warmer than the uninsulated MacroBin. The insulated bin ended with a stuck fermentation at about 1° Brix, while the other fermentations finished dry.

The fermentation in the Apollo tank followed what I have heard is typical for egg-shaped tanks. The cap was deeply dense and very compact on its surface. The liquid level was at about the same depth as what would be found in most traditional fermentations, but because the top narrows significantly, the majority of the cap was immersed in the wine 100% of the time, which is considerably more than the wider surface area of the MacroBins.

Chambourcin, the grape variety used in this comparison, is a variety with lots of color but with less tannin than one would expect given its depth of color. In this study, the MacroBin wines were normal in color, while the Apollo wine was more intense. Again, there was no difference in either MacroBin from a tannin perspective, and the tannin level was similar to previous fermentations of Chambourcin in MacroBins. The Apollo tank, however, did have a rather substantial increased tannin extraction compared to the MacroBin-fermented wines.

On the East Coast, fall temperatures often drop right around the time warmth would come in handy for red wine fermentation. Many wineries try to insulate their bins so they don’t lose as much heat. True insulated bins do retain the heat and, in our case, too much heat was trapped. 

It appears that for the uninsulated MacroBin, the low fruit height relative to its large surface area allowed heat to escape from the sides and surface much more quickly than either of the other two tank types. The fermentation temperature just could not keep up with that type of heat loss in the uninsulated bin. The insulated bin, on the other hand, retained too much heat, and the cap got too warm, resulting in a stuck fermentation. While this is not usual, it is important to be aware that it can happen more easily in this type of tank.

The Apollo tank benefitted from the egg design and conserved enough heat for fermentation flavor extraction and color, but it didn’t over-heat the wine.

Concrete egg fermentations follow a very similar protocol with that of the Apollo tank. Based on conversations with winemakers who use the concrete eggs to ferment, the mass of the concrete seems to moderate the fermentation temperatures for red wines, so even though there is not as much heat radiated away from the tank, the concrete absorbs the heat from the wine’s fermentation.

If concrete eggs are used for fermentation, it is easier if the tanks have a manway to allow removal of the remaining skins. The Apollo tank is light enough that after removal of the free run, the remaining must can be poured directly into a press. There is a lifting harness available to allow a forklift to raise the tank, so that skins can be poured or scooped into the press.

At the end of harvest, all of the egg types can become wine-storage vessels, while MacroBins go into the storage barn.

If the egg shape is the critical criteria to get the concentration of flavors, and you believe using it increases complexity or other wine attributes, it is time to decide what is the best container for the wine you want to make.

As a winemaker, I would like to have all of these tools available. I would be pleased to have the visual presentation of the concrete eggs: They provide a similar expansive appearance for the winery that large stands of stainless steel tanks or large stacks of barrels provide. However, if in order to produce the volume of wine that you need to meet your business plan, your bank account cannot afford the cost of the concrete or ceramic eggs—or if your winery does not have the space to dedicate to 3,000- to 5,000-pound concrete eggs as fixed structures—then an Apollo egg might be a good alternative for some or all of your wine production. Provided your wine cellar has good temperature control, an Apollo egg should provide many of the benefits of the concrete egg tanks at a fraction of the cost.

Many small wineries using MacroBins for fermentation need to think seriously about their use of those bins only for their intended purpose: bringing grapes to the winery. Put the bins aside and use an egg-shaped tank for small-lot fermentations. The winery will be rewarded with better wines made this way. Either way, concrete, ceramic or plastic, there are good reasons that the egg-shaped tank is here to stay.

Dr. Richard Carey is a wine consultant in Lancaster, Pa. He wrote a software program to help small wineries keep track of their wine production records and results of laboratory analyses.


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