Corks and Other Closures

Apr 14, 2010 by Diane Davis

We were excited to go to Moore Family Winery a couple of Friday’s ago and listen to a presentation by Adolfo Hernandez, QA Supervisor at www.masilva.com to the local winemakers and vineyard owners.  The presentation was part of the services of the Lake County Wineries Association as part of their ongoing efforts bring in vendors to share with the wineries ideas on how creating cooperative purchasing of supplies which can then reduce the cost of  producing quality products.

The presentation was so interesting that, as a lay person, I not only understood, I was enthralled with the information.  Later that day I emailed Adolfo and asked him if he would write an article to share with the readers of Winestyle Living on corks and other closures.

So, without further ado, I present Adolfo Hernandez:

There is probably no other topic in winemaking that is as polarizing or emotionally charged as closures. Wine itself is a passionate topic, more art than science, but that attractive ambiguity provides a poor context to objective discussion. It’s not a stretch to say that a descriptor like ‘floral, with honey notes’ is infinitely sexier to most people than ‘2-phenylethyl acetate’. In the same vein, it’s easier to say ‘corks ruin 15% of all wine!’ rather than exploring and understanding all the reasons behind spoiled wine, which can stem from closures, winery and vineyard practices, transport, or consumer judgment.

Below are short overviews on the three dominant closure types. I’ve provided a few references for the inquisitive types that want to know more, but there are literally books written (I suggest George Taber’s To Cork Or Not To Cork) and waiting to be written on the subject. For plastic corks I make no mention of the polymers used, don’t expand on the benefits and drawbacks of manufacturing approaches, or talk about technical specifications. There is no discussion here on the topic of reduction chemistry for screwcaps, or on the bravery of those pioneering winemakers in Australia and New Zealand. For natural cork, I don’t explain the life cycle of the cork oak (they don’t get cut down to make corks!) or the manufacturing processes. I make a mention of TCA, but don’t go into the origins and effect of other haloanisoles or chemicals that have similar properties. In regards to all three, there are no comparisons of environmental impact, oxygen transmission rates, bottling practices, or market acceptance.

Natural cork

Natural cork is the traditional method for sealing wines, and the near exclusive choice for prestigious and expensive bottles.

The drawbacks to cork stem from its origin – it is a natural product, and subject to inconsistency and imperfections. Visual quality is subjective, and there is the possibility of critical defects that can compromise the seal of the wine.

The most prominent defect is the ability of corkwood to absorb and impart haloansioles into wine, the most common of which is 2,4,6 trichloroanisole (TCA). TCA is formed from the interaction between certain species of molds with chlorophenols, which are common cleaning and disinfecting agents. Identification of TCA in 1982¹ as the chemical most responsible for forming cork taint contributed to gradual shifts in industry practices, resulting in dramatic decreases in the incidence of tainted bottles. Anecdotal rates of taint usually quote 5-10% without references, but scientifically validated tests put the number of bottles tainted by TCA at less than 1%.

Natural cork is used for all ranges and types of wines, with different grades and lengths available to complement the intended price point and packaging.

Synthetic Corks

Manufactured plastic stoppers provide the great advantage of being consistent, inexpensive, TCA-free, and highly customizable. One major benefit for wineries intending to use synthetic corks is that they are fully compatible with standard bottling equipment.

Synthetics can be produced either through extrusion or injection molding. Extruded stoppers result in one long, continuous tube that is later cut into the appropriate size, while injection molded stoppers are created individually.

Synthetic corks are intended for short-lived wines which should see quick rotation. In general, synthetics do not maintain a long-lasting seal against the neck of a bottle and can lead to oxidation after several months^2,3.

Screwcaps

Screwcaps, also known as ROTE (Roll-On Tamper Evident) closures or by the trade name Stelvin, provide tight, consistent seals without the chance of carrying TCA. Screwcapped bottles do not have to be stored on their sides, can be easily opened and closed, and are inexpensive in comparison to higher-grade natural corks. Metal caps do not absorb halophenols or other volatile compounds from the environment, and impart no aromas or tastes to enclosed wine.

Screwcaps are produced from aluminum, with inside liners made of either tin or saranex with varying levels of gas permeability.

The chemistry of post-bottling development of wines is not yet fully understood, but the tight seal and low to negligible oxygen transmission rate (OTR) of screwcaps is considered to be a contributor to the ‘reduced’ aroma characteristics endemic to this closure. There are some fascinating reads^4,5 to be found on this topic, especially for those with backgrounds in chemistry.

Screwcaps are predominantly used on aromatic white wines such as riesling, pinot grigio, and most famously sauvignon blanc.

Here are a few references. Should it be available to you, peer-reviewed scientific literature is the closest thing you will ever find to unbiased, objective facts. I do include a link to a Dr. Alan Limmer article as he’s usually a fascinating read.

1. Buser, C. Zanier, H. Tanner – Identification of 2,4,6 Trichloroanisole as a Potent Compound Causing Cork Taint in Wine. Journal of Agricultural and Food Chemistry, 1982, 30, 359-362

DOI: 10.1021/jf00110a037

1. Lopes, P.; Saucier,C.; Glories, Y. – Nondestructive Colorimetric Method to Determine the Oxygen Diffusion Rate through Closures Used in Winemaking. Journal of Agricultural and Food Chemistry; 2005, 53, 6967-6973. DOI: 10.1021/jf0404849

1. Lopes, P.; Sacier, C.; Glories, Y.; Teissedre, P.; – Main Routes of Oxygen Ingress Through Different Closures into Wine Bottles. Journal of Agricultural and Food Chemistry, 2007, 55, 5167-5170. DOI: 10.1021/jf0706023

1. Limmer, Alan – The Chemistry of Post-Bottling Sulfides in Wine. Chemistry in New Zealand, 2005. http://nzic.org.nz/CiNZ/articles/Limmer_69_3.pdf

1. Lopes, P.; Silva, M.; Pons,A.; Tominaga,T.; Lavigne,V.; Saucier,C.; Darriet,P.; Teissedre,P.; Dubourdieu,D. – Impact of Oxygen Dissolved at Bottling and Transmitted Through Closures on the Composition and Sensory Properties of a Sauvignon Blanc during Wine Storage. Journal of Agricultural and Food Chemistry; 2009, 57 (21) 10261-10270 DOI: 10.1021/jf9023257

Adolfo Hernandez

QA Supervisor, M.A. Silva Corks, USA

adolfo@masilva.com, www.masilva.com