The Cork Confusion
Importance of a cork in a wine bottle can never be taken lightly. Kailash Gurnani conducts an experiment with five different corks to gauge their affect on wines.
It was in the second year of my Bachelor of Oenology (Winemaking) that I was introduced to the concept of closures in wine and how important they are in winemaking. One wrong choice at the last stage of winemaking i.e bottling, can pretty much ruin the months or even years of hard work put into a wine.
One of the most crucial aspects of a closure is its oxygen transmission rate or OTR. It is nothing but the amount of oxygen that transmits through the closure and comes in contact with the wine. Naturally, a poor seal will have a high OTR, which can be detrimental to the quality of the wine
Natural corks have been used for closure for the large part of modern winemaking history due to its ability to form a good seal and allow for some ageing in bottle. But they gathered a bad reputation due to the presence of TCA in some batches. TCA (2-4-6 Trichloroanisole) is a chemical which when present in the cork is responsible for damp, musty, mouldy and newspaper type off-flavors in wine. Over the last few years manufacturers have found effective ways to eliminate TCA during the production of corks.
Most of the winemaking world has shifted to or is shifting to screw caps as it is considered to be a near perfect seal. Screw caps have become known to preserve wine very well in bottle as their OTR is much less than that of corks. However, screw caps can be responsible for reduction in the bottle due to the absence of air. A reduced wine is one that is unexpressive, closed, flat and in some cases can result in production of off-flavors inside the bottle. Screw caps also don’t provide the required OTR for red wine ageing. This is why most premium and full-bodied age worthy red wines are almost always bottled under corks.
A lot of dollars have been spent behind the research of OTR and its impact on the quality of wine. Some people have measured the rate of oxygen transmission and dissolved oxygen in wine over time to see how it affects the wines’ sensory properties.
All said and done it is the winemaker, his winemaking style and the market that determines the choice of closure. I decided to do my own little trial to see how my wines aged under different closures.
12 months ago while the 2012 York Sauvignon Blanc was being bottled, some bottles were sealed with Synthetic, Bidisc, Natural & Micro-granulated corks. All these bottles were bottled under the exact same conditions one after the other. They were then stored together in the horizontal position at a temperature of 18-21 degrees Celsius in York’s underground cellars. I opened and tasted these wines last week to compare how they had developed with time. (Unfortunately I could not perform trials under screw-caps. I hope to do that this year with the 2013 whites and reds.)
Synthetic Cork: It is made out of plastic to replicate the properties of natural corks without the problem of TCA.
Pros: Cheap, free of TCA
Cons: Does not have the same compression and expansion qualities as natural and other corks. High OTR
Bidisc Cork: They consist of a cork disc at the top and bottom of the body that is made up of many small fragments of corkwood glued together.
Pros: Cheaper than Natural corks, free of TCA
Cons: The glue used to hold the small cork fragments can impart a foul taste in the wine
Natural Cork: Manufactured from the bark of Quercus Suber trees.
Pros: It has good compression and expansion properties to form a tight seal while allowing for some oxygen transmission to age the wine.
Cons: Cork performance can be inconsistent since they are naturally produced from the bark of trees that do not have a uniform internal structure leading to TCA taint. Expensive compared to Bidisc and Synthetic.
Micro-granulated Cork: Corkwood is ground completely and after a screening process, the fragments of the same size are glued together using a special adhesive.
Pros: TCA free. Predictable OTR as each cork manufactured is consistent. It has good compression and expansion properties to form a tight seal.
Cons: Expensive than Natural corks
There are several manufacturers who make micro-granulated corks under their patents. In this experiment DIAM3 & DIAM5 corks were used. The number 3 and 5 indicate the OTR with DIAM3 having a higher OTR than DIAM5.
Difference in appearance
In the image, the wines from left to right were sealed under DIAM5, DIAM3, Natural cork, Bidisc cork and Synthetic cork respectively. The wine under Synthetic cork (extreme right) was darker than all the other four wines indicating a higher oxygen contact. Among the remaining four wines, the wine under Bidisc cork (second from right) seemed to be slightly darker than the DIAMs and Natural cork. There wasn’t any noticeable difference in color between the DIAMs and natural cork.
Synthetic vs Bidisc vs Natural Cork
I found the wine sealed under Synthetic cork the poorest of the three in terms of taste and quality. The wine was one dimensional and lacked complexity. The tropical flavors that the wine once had were missing. Instead, I could smell and taste some oxidized flavors. The herbaceous and grassy characters were aggressive on the nose with some cabbage like aromas. On the palate the wine lacked balance and the mid palate was flat. The acid balance was completely out of place with a lot of bitterness on the finish.
The wine under the Bidisc cork seemed to have retained some green apple and pineapple flavors. However, the herbaceous flavors were still dominant in the wine. On the palate, the wine had better structure and acid balance than wine under Synthetic cork with the bitterness on the finish from the synthetic cork absent. Overall, a huge leap in quality was apparent in the wine from Synthetic to Bidisc.
Natural cork performed the best of the three. This wine was more tropical in nature than herbaceous. The palate was balanced and linear with no bitterness whatsoever. If not for the wines sealed with DIAM’s, I wouldn’t have ever guessed how much better this wine could have tasted a year after it was bottled.
DIAM3 vs The Above
All said and done, a wine can score top marks only if it has finesse. Finesse is nothing but the way in which all the flavors of the wine come together in perfect harmony. DIAM3 did exactly that. The manner in which the green apple, mint, pineapple, guava, lemon, asparagus and capsicum aromatics came through was seamless. The flavors, structure, length, body and acid balance of the wine was near perfect. The DIAM3 was significantly better than the Bidisc and Synthetic cork wine and only marginally better than the wine under Natural corks.
DIAM3 vs DIAM5
The wine under DIAM5 was by far the most well preserved wine; almost a little too much for my taste. The wine was smooth but closed. None of the flavors jumped out of the glass like they did in the other 4 wines. It was almost like the aromas were tied up to a leash inside the glass raring to get out. I let the wine breathe for 15-20 minutes and slowly it started to taste like the wine under DIAM3, flavorsome, fresh and balanced.
What about Screw caps?
In this particular case, i.e. white wine like Sauvignon Blanc, I can safely say that the quality of the wine would have been in the same territory as those sealed with micro-granulated corks. That means, the wine would have been well preserved, but perhaps a little too closed and unexpressive at the start only to open up with time.
For me, the micro-granulated cork (DIAM3) is hands down the winner here. We live in a day and age where we want everything to be perfect from the word go and that is exactly what the wine under micro-granulated corks was. After going through several research papers that compared the performance of various types of corks, I was pleased to see that my results were in line with those carried out in a much more scientific and controlled manner. I am already looking forward to open these wines again in July 2014 to check on their evolution after two years in bottle.
All views expressed here are the author’s own
He tweets at @desiwinemaker
Image courtesy Kailash Gurnani