The Cork Test

 

Halter Ranch Vineyard

Molly explains the process

 

Similar to separate lots of wine from the same vineyard block, different lots of cork are sourced from the same forest.  Each year as we prepare to place our cork order, we receive sample bags containing small portions (around 50-100 corks) from a variety of cork lots.  Corks are graded by quality, so all lots we receive are graded at the same quality standard by the producer but before we decide on which lot we will purchase the years corks from, we put each batch through our own battery of tests to insure our standards are met. This week, Molly set aside a few moments to run us through the various tests in order to offer us a firsthand look into the process. 

 

Halter Ranch Vineyard

Little corks all immersed in unoaked chard

 

The principle enemy of cork, and subsequent spoilage in wine, is a mold called Trichloroanisole (2-4-6 Trichloroanisole or TCA) which accounts for a 1-3 percent spoilage rate in wine stored under cork based on the off (moldy cardboard, dirty sock, rotten banana) odor it causes when it interacts with fermented juice.  So the first, and most critical, among our three primary tests is a sensory evaluation.  We immerse corks from each lot overnight in unoaked white wine within a glass container under a teflon lined cap.  Teflon, unlike plastic or rubber, does not absorb TCA so it is important that the portion of the cap in contact with the wine and cork be teflon to avoid muddled results.  Additionally, oak character can mask the presence of TCA so it is important that the test wine be unoaked.  After the corks soak in their containers overnight, the caps are removed and the containers are left to sit for 10 minutes allowing the headspace (air) in each bottle to equalize.  Then staff members move through to smell each container.  If any cork lot shows TCA presence, it is removed from the running and no further tests are performed on it.

 

Halter Ranch Vineyard

Gloves are important to avoid contamination

 

It is absolutely critical for each cork to fit snugly and seal properly in the bottle to avoid spoilage from oxidation.  We order corks in specific dimensions to suit the particular bottles we use for our wines.  Length and diameter are measured for each cork from each lot.  Lots fail if 1 percentage point worth of corks are smaller than 23.5 mm in diameter or 4% are larger than 24.5 mm in diameter.  If 10% of corks in a lot are 1mm under or over the desired length, the lot also fails.

 

Halter Ranch Vineyard

Comparing teflon and rubber

 

We then test for breakage potential by flexing each cork backward and forward (this test requires strong, dexterous fingers!).  If 10% of corks break or crack unacceptably, the entire lot fails.

 

Halter Ranch Vineyard

Measuring

 

The final test involves grading each cork lot visually to insure it meets our expectations as to the quality level we’ve requested.  Corks are graded upon the quality of grain and the presence of pores, cracks, or depressions. Each cork is then given an A, B, C, or D (A being best and D being unnacceptable).  An  aggregate score is then created for each lot and we choose based upon the best overall score.

 

Halter Ranch Vineyard

Lindsey B performs sensory evaluation

 



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