Pomeroy Cellars

Boutique Winery and Tasting Room


Why do we use corks at bottle stoppers?

Posted on June 15, 2017 at 1:25 PM


Left: Cork Oak Right: Cork factory
Taken by Winemaker, Dan Brink, on a tour of a cork factory in Portugal, 2014

Why do we use corks for bottle stoppers?

Cork is a wonderful natural and renewable resource. Cork as we know it is a layer of the bark on a Quercus Suber, more commonly called the Cork Oak tree. The Cork Oak tree is an evergreen oak tree predominantly located in Southwest Europe and Northwest Africa and may commonly live to more than 200 years old. Of the Cork Oak forests worldwide, 34% are found in Portugal and 27% in Spain. The majority of the cork used in everyday life is derived from these two countries- 50% coming from Portugal.

Cork is used in numerous capacities because of its unique qualities. Cork is impermeable to moisture, buoyant, fire retardant, and elastic. Cork is most commonly associated as a bottle stopper in the form of a wine cork, but it is also used as insulation, fishing floats, gaskets, flooring, bulletin boards, in woodwind instruments and a sundry of other small, but never underrated capacities. Most importantly cork is a renewable and environmentally friendly product.

The harvesting of the bark of the cork oak, the material that is cork, is done without harming the tree in any capacity. The first bark is harvested when the cork oat is 25 years old and then harvested only every 10-12 years following. The bark may be harvested from a cork oak tree about 12 times in the tree's lifetime. The process is done without any machinery and usually requires the manual labor of five skilled individuals in order to avoid harm to the tree and maximize the quality of the cork/bark harvested.

There are numerous closures for wine bottles, corks being the oldest and perhaps still most common. There are also aluminum screw-off caps, poly-seal (plastic) screw-off caps, various caps with cork or synthetic plugs that plug and cap the wine bottle, synthetic "corks" that appear as a cork in the bottle but are plastic or rubber material, and more. All of these different closures range in price and purpose. How much does one want to spend on the closure? What are the goals- some oxygen contact through the closure or none? At what rate and percentage should the oxygen contact the wine through the aging process? How long is the closure meant to last- 2 years? 5 years? 20+ years? What is the desired feeling to be generated in the customer opening the bottle? Will the wine be stored upright or on its side? These are all questions producers ask themselves when selecting wine bottle closures.

Currently we use cork exclusively for our wine bottle closures. We primarily use two different cork stoppers. For our red wines that we intend to be age worthy and last well beyond the ten year mark we use a solid cork stopper. These wine corks are from some of the highest quality cork bark harvested and are made by making a solid punch (similar to a hold punch) through the bark to create a solid piece of cork. The corks are then "rated" by cork density- the more dense and compact the rings of the cork bark the higher the rating of the solid cork. The higher the rating of the cork, the more durable, lasting, and effective the cork will be. For age worthy wines that will be in the bottle with this cork for an extended duration of time the quality of the wine cork is crucial. The cork will not only keep the wine in the bottle, but will keep bacteria, yeast and other microorganisms out all while allowing oxygen to permeate the cork at a slow, but steady rate aging the wine to beautiful maturity for 30 + years. If one intends to age wine for an even longer period of time, the cork should be changed because it will deteriorate over time.

The second most common wine cork we use is still 100% cork, but it is made from the cork bark which may have flaws and is not suitable to make the high quality, solid corks. These corks are made from crushed pieces of cork that are then compressed under high pressure and adhere together. These wine corks then have a disc of solid cork glued to each end to provide an extra layer of protection since the wine cork itself is not one solid piece. We use these corks for our white and rosé wines and other wines made to be consumed within five years. These wines do not need to the long term protection of the solid wine cork, but the wine still gets the benefit of the cork permeability to oxygen and protection provided by the unique cork characteristics.

It is our desire that our wines experience managed oxygen exposure once in the bottle and during the aging process, whether that aging is one year or 20. We don't want the wine to "oxidize" or turn to vinegar (those often sharp and astringent characteristics of "next day" wine), but some oxygen is crucial to the continued growth and development of the wine. Wine is a living organism that changes and evolves with time and controlled oxygen exposure is key to that evolution.

There are closures other than cork that allow for controlled oxygen contact with the wine. Many screw-off tops are theoretically designed to allow a certain number of parts per million of oxygen through the cap and in contact with the wine. There are numerous studies comparing various types of closures and the benefit of oxygen contact with wine in the bottle. Like anything else, one may find research to support whichever closure they prefer as the studies are still somewhat mixed and thus, to us, inconclusive. We choose cork because it is an organic substance, it is a renewable resource, it is also completely recyclable. Not to be understated, there is still something so romantic and traditional about pulling the cork from a bottle of wine.

What about "cork taint"?


"Cork taint" or a "corked" wine bottle refers to TCA, 2,4,6-trichloroanisole, a compound resulting from the interaction of plant phenols, mold, and chlorine. It can grow on tree bark, but it may also be the result of environmental conditions being "just so" to facilitate the growth of this destructive compound. Currently the number two reason that producers use alternate closures is to avoid "cork taint." Although, this is closely linked to the number one reason, cost, because damaged wine equates to an increase in costs.

"Cork taint," TCA, is identified by wet cardboard, wet dog, musty, moldy smells and flavors in the wine. As of 2012 a study conducted by Wine Spectator found TCA existed in 3.5% of wines. Most individuals do not have a sensitive enough palate to notice small levels of TCA. If the same characteristics are found in a multitude of wines by a given producer or even across the same vintage, it is likely not a result of TCA, but rather some other flaw.


TCA is a risk when using wine corks as bottle stoppers. There are several precautions to take: sanitize the corks prior to use, sanitize all bottles and related equipment, keep the production facility clean and free of spores and microorganisms that may wreak havoc if allowed to "feed" and multiply (don't get them wet or feed them after midnight, that sort of thing) and verify the seal after inserting each cork into the bottle to be sure it is evenly inserted and was not damaged in any way during the process.

In our opinion there is no "right" or "wrong" to wine bottle closures, there are simply choices and various reasoning supporting those choices. There may be a multitude of quantifiable reasons for one choice or another, one preference over another, but at the end of the day is it any more complicated than, "do you prefer white or red?" Do you prefer a cork or a screwoff-cap?


"Wine can of their wits the wise beguile, make the sage frolic and the serious smile." -Homer

Written by Destiny





Categories: Q and A, Wine Making

Post a Comment


Oops, you forgot something.


The words you entered did not match the given text. Please try again.

Already a member? Sign In

1 Comment

Reply lilaluna
5:32 AM on January 3, 2018 
I truly value this post. I've been searching all over for this! Thank heavens I discovered it on this blog . I truly respect your work and i seek in future i will return after more data. like this one.You have filled my heart with joy! I have some good work experience with best essay writing service ( https://www.buybestessaysonline.com )and my words are clearly based on what I felt through such processes in the past.