What could be more synonymous with celebration than popping a cork? For generations, that signature sound has signaled the start of festivities, and we’ve collectively come to associate it with feelings of cheer and excitement at the good times ahead.

But for all the appeal of this festive image, the classic cork is not as universal as it would seem, and there are in fact several alternative closures available to winemakers, each with their own pros and cons.

In this article, we’ll survey the four principal closures used to seal wine bottles, and consider some of the important factors that go into their selection.

Natural Cork

Natural cork is the most traditional closure, and boasts a history of universal use that goes back many centuries.  

Made of a single piece of cork oak bark, generally harvested by hand, the traditional benefits of natural cork are that its soft enough to form a proper seal against the neck of the bottle, firm enough to maintain its integrity, and porous enough to allow for microoxygenation of the wine during aging - a factor considered crucial to the development of more interesting and complex aromas.

But like all things, natural cork has its downsides. For one, it is expensive, ranging as high as $1 a bottle, and as a natural product, there tends to be some variation in its porosity, leading to unpredictable effects on long-aged wine. In fact, one can sometimes see and taste differences between otherwise identical aged bottles of the same wine simply because of the variance in oxidation afforded by corks of differing porosity.

Natural cork is also susceptible to TCA (Trichloroanisole), a chemical compound which can be transferred into the wine, spoiling the bottle. TCA contamination has been the primary driver for premium wine producers to look towards alternative closures.

But for all that, natural cork is generally reliable, organic and sustainable, and has an undeniable aesthetic appeal as the “original” closure. There’s a certain charm to drinking from bottles sealed just as they were in our great-grandparent’s time.

Composite cork

Next up in the list is composite or agglomerate cork; a stopper made of granules of natural cork pressed and bound together by a food-safe adhesive. You can tell composite corks by eye; where natural cork is smooth, perhaps with a few air pockets and more or less uniformly colored, composite cork is darker, rougher, and, well, looks like many little particles pressed together.

Composite corks come with their own pros and cons. On the plus side, they are cheaper than natural cork, and in almost all cases TCA free. Like natural cork, they allow for micro-oxygenation of wine during storage, and they also manage to maintain that traditional “corky” feel.

On the downside, unless winemakers spring for more expensive “micro-agglomerated” cork made with tiny particles, they are generally not as long-lasting as natural cork. This limits their application to wines intended for younger drinking.

In addition, while the adhesive is technically food safe, many winemakers feel uneasy about allowing their wines to come into extended contact with a synthetic binder.

Synthetic cork

Third in the line are synthetic corks. While these take the same shape as natural cork, synthetic corks are made of plastic.

The benefits of synthetic cork are their consistency, durability, and again, absence of TCA. Like the other two they allow for stable oxygen exchange between the bottle and its environment, and as there is no risk of them drying out, bottles can be stored upright rather than horizontally. And, of course, synthetic cork is cheaper than natural or composite cork.

However, being made of plastic, synthetic corks are considered much worse for the environment, and are not biodegradable. Being the firmest of the three, they are also more difficult to pull from the bottle, and can be nearly impossible to put back in.

Screw caps

Last of the four main categories are screw caps; easiest to open and reseal, and cheapest to produce. So while the crack of opening a screw top may not be as satisfying as the popping of a cork, many producers around the world are turning to screw caps as an alternative.

Screw caps, however, offer effectively zero oxygen exchange between the inside of the bottle and its environment. This is good in that winemakers can ease up on the amount of antioxidant sulfur in the wine, but potentially bad for the age-ability of the wine, as conventional wisdom holds that small amounts of oxygen are beneficial to a wine’s development.

In either case, screw caps, like synthetic cork, have the downside of a negative environmental impact. While the aluminum is theoretically recyclable, the plastic liner is not.

Choosing a Closure

There’s a lot for winemakers to consider when choosing a stopper.

Naturally, high on the list is the cost. As mentioned earlier, natural cork can run as high as $1 a pop, while screw caps are only a couple of cents each. While premium bottles might be able to absorb the higher costs, entry-level wines cannot.

The end result is that natural cork will be found primarily in high-end bottles, further cementing the association of natural cork with premium wine - despite the risk of cork taint from TCA.

In addition to cost, there is the question of porosity; the amount of air the closure allows to filter through. While too much air will cause premature oxidation of the wine, many argue that a small amount of oxygen during aging allows the wine to develop more interesting and complex aromas.

For better or for worse, another important consideration is tradition. There is an aesthetic component to opening and drinking a bottle of wine, and whether for historical reasons (using the same materials our great-grandparents did) or environmental reasons (getting away from plastic at least for a minute) there is a charm to genuine cork that is unmatched by its synthetic alternatives.

This is particularly true for vignerons committed to organic winemaking. While some are a little more relaxed, many organic winemakers don’t appreciate the idea of their wine coming into contact with plastic cork and synthetic adhesives. Additionally, these winemakers are often environmentally conscious, and don’t appreciate the idea of generating more plastic waste either.

At the end of the day, the choice of closure comes down to a question of economics, principle, marketing and personal preference.

What about Burgundy?

Burgundy, as we are fond of mentioning, has always had a knack for combining progress with tradition. While natural cork still abounds, particularly among more expensive wines, composite corks are rapidly growing in popularity.

Retaining the charm and traditional feel of natural cork, composite corks allow for the precise control of oxygen ingress, are cheaper than natural cork, and are virtually devoid of the risk of TCA cork taint. And while most composite corks have a relatively short lifespan, as mentioned above, higher-end composite closures can stand the test of time. Indeed, a micro-agglomerated cork known as DIAM has found increasing use in Burgundy, particularly for white wines which generally are meant to be drunk younger. DIAM corks are even used by many on Grand Crus!

Even the concerns of organic and biodynamic growers are being addressed. New composite corks which make use of natural binders like beeswax and vegetable polyols satisfy their preference for plastic-free organic stoppers, further expanding the use of composite corks.

For their part, while screw cap wines can be found in Burgundy, they are not nearly as popular as the alternatives. In part this is due to a near-hermetic seal, which stifles the wine during aging, but perception and tradition play a likely role as well.