How to Purchase Wine Corks

The ultimate guide to purchasing wine corks.

By Kinnek Community  |  September 25, 2016

We’ve summarized some key questions to consider for your business when purchasing wine corks. Use these as a reference whether you’re a first-time winemaker or looking to establish a new production line.

What is a wine cork?

Since their rise to popularity in the 17th century, wine stoppers made from the bark of cork oak trees have remained the most commonly used wine stoppers in the world. Cork became the gold standard in wine stoppers because of its natural ability to very effectively seal glass bottles, preventing damaging oxidation.

Today, there are three major categories of corks to choose from:

Carolina Wine Supply natural corksNatural corks are made from one solid piece of cork, cut from a sheet of cork bark. This cork comes in a variety of grades based on surface, water content, porosity, and visual inspection, and will vary in price accordingly.

Manufactured corks are made by enhancing the sealing properties of all or part of lower grade corks:

  • Colmated corks are made when low quality, porous corks are coated with adhesive and filled with cork dust to create a smooth and solid stopper.
  • Agglomerated corks are made by grinding excess cork into small particles that are then formed into solid sheets of cork using adhesives.
  • Sandwiched corks are made when a lower-grade agglomerated cork is sandwiched between two slices of top-quality natural cork to improve the seal.

Synthetic corks are made from plastic compounds designed to look and act like natural corks.

How does a wine cork affect aging?

The complex oxidation process is a vital aspect of aging wine. While exposure to too much oxygen will ultimately damage wine, a small amount of controlled oxidation is important for removing unpleasant aromas that can form under anaerobic conditions.

It is widely held that the best corks allow close to 1 milligram of oxygen to enter the bottle each year.  

According to The Wine Celler Insider, “this small amount of air is seen as perfect for helping age-worthy wines develop their complexities while the tannins are busy softening.

AROL automatic corking machineWhat type of cork is best for my wine?

One of the most important considerations when choosing the right cork for your wine is how long the wine will be in the bottle before consumption. Corks are rated based on the length of time they will protect the wine from harmful oxidation:

  • Natural corks: 5-20 years (depending on quality)
  • Agglomerated corks: up to 5 years
  • Synthetic corks: 2-3 years

For long-term storage, natural cork remains the clear choice. It is the only corking option that has proven its effectiveness in preserving wine for extended periods of time. With 80% of all wine still being closed with natural cork, according to Wine Enthusiast, you can feel confident in its performance.  

The popularity of natural cork is also partially due to consumer demand. Many customers still prefer the most traditional and natural options available.

However, more affordable synthetic corking options are on the rise for a few reasons. According to WineMaker, the majority of wine is consumed within a few years of production and often a few hours after purchase. This makes the higher cost of natural corks rated for 20 years impractical for these wines.

Synthetic corks also carry other benefits. For example, they can prevent a rare but destructive phenomenon known as cork taint. According to Wine Folly, somewhere between 1-2% of natural corks used today end up tainting wine with a moldy smelling substance called trichloroanisole. Synthetic corks completely eliminate this risk.

Finally, synthetic corks are remarkably consistent in their oxygen transmission. That means winemakers can control their desired rate of oxidation by choosing specific synthetic corks. This provides wine producers with the option of creating highly consistent flavor profiles over natural variation.

For those wishing to maintain the tradition of natural cork but who do not require the 20 year rating for their wine, agglomerated corks can fit wine producer’s practical, aesthetic, and economic needs.

Reliable Cork Solutions slimcorkWhat size cork do I need?

The size of your cork will depend on the size of your bottle. The opening of a standard, 750 ml wine bottle is 3/4 of an inch. These bottles can take corks in sizes #7, #8, and #9.  Use of #7 is generally not recommended unless you are corking by hand.

While, #9 corks are considered by many to be the ideal size, #8 corks are popular because they provide a good seal and can be inserted with the majority of corking machines available, including hand corkers. To insert #9 corkers, a floor corker, semi-automatic, or automatic corker is usually required.

Do I need a specialized cork for sparkling wine?

Sparkling wine corks are typically composed of an agglomerated body with a natural cork disk adhered to the bottom. These corks also have a larger diameter to withstand the high internal pressure generated by sparkling wine.

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