Cork Quality Council 
Quality Control Procedures

1. Inbound Cork Shipments
2. Outbound Cork Shipments
3. Agglomerated Cork Construction

Incoming Cork Procedures

I. Sampling Plan

II. Acceptance/Rejection

III. Test Procedures

A. Sensory Test:
The number of corks to be tested will be in accordance with Mil Std 105-D. Six corks from each bale taken as per III.A1 above will be immersed in a 500ml container of neutral dry white wine for 24 hours, then checked organoleptically for changes in sensory character when compared to a control wine. If TCA taint is suspected, an immersion test will be made from six corks from every bale. Any bale with TCA taint will be rejected. 

B. Visual Quality:
Corks sampled, at minimum, will be in accordance with Mil Std 105-D (reduced). Individual corks are classified into predetermined categories depending on the physical qualities agreed on with the producer. 

C. Moisture:
Cork moisture will be tested on a sample size of 25% of the Mil Std 105-D (reduced) per lot. A cork moisture instrument will be used. Cork shipments should be received with a moisture level below 8% average, with a tolerance per AQL 4.0.

If moisture level average is above 8% but below 10.5%, the following procedure may be followed: 

• Corks are to be placed in a drying area which is physically separate from the storage area for accepted corks. 
• When corks are resampled for reduced moisture levels, the cork moisture will be tested on a sample size of 25% of the Mil Std 105-D (reduced) per lot. A cork moisture instrument will be used. Moisture level must be below 7.5% average, with a tolerance per AQL 4.0. 
• All sensory testing must be done again following procedure outlined in III.A before corks can be accepted into ongoing inventory of corks suitable for sale. 
D. DIMENSIONS:
Cork dimensions will be checked on a sample size of 25% of the mil Std 105-D (reduced) per lot using an electronic or dial caliper accurate to +/- 0.01mm. Tolerance range per ISO3863 and acceptance at Military Standards 105-D. 
Diameter: as specified (+/- 0.50 mm) AQL = 1.5 Length: as specified (+/- 1.00mm) AQL = 4.0

E. RESIDUAL OXIDANTS:
One cork from each bale taken as per paragraph III.A1 above will be tested using a qualitative analysis involving the reaction of potassium iodide with residual oxidants in the presence of a starch indicator. A change in the test solution from clear to blue/violet color is a positive result.

Acceptance: 

• Traditional washed: per CTCOR 
• Peroxide washed: ZERO 
• Natural (Metabisulfite): ZERO 

A lot is defined as a particular wood quality, size, and wash from an individual supplier in a single shipment.

V. Records 

Permanent records of the quality control tests for each lot will be kept by the Supplier for a period of at least five years. 
 
 

Outbound Cork Procedures

A. BATCH QUALITY 
The batch quality should match any samples presented to clients on which the order was based. Cork samples sent to a client should contain a minimum of 24 corks.

B. CORK MOISTURE
Randomly sampled corks from the prepared batch are analyzed using the sample procedure outlined in Incoming Cork QC. Prepared batches should have an average moisture range between 5% - 8%.

An injection of at least 2 grams of sulfur dioxide should be added to each bag of corks for the control of micro organisms.

III. Records 

Permanent records of the quality control tests for each lot will be kept by the Supplier for a period of at least five years. 

IV. General

Every reasonable effort will be made to ensure the pristine character of the corks is preserved while in processing at members’ facilities.
 
 

CQC Standards for 
Agglomerated Corks with Disk

Compress cork to a diameter of 1/3 the original size allowing deformation for 24 hours. Diameter is measured as a percent of the original size after 15 minutes.

Acceptable values: Min 80% Target 90-95%

Measure agglomerated cork - without disks - at max 6% humidity level(1) Measurements recorded as a ratio in terms of Kilograms per cubic meter.

Acceptable Values: Min 255kg Max 320kg

Treated stoppers are marked and placed on their bases in a colored ethanolic solution containing 10% alcohol by volume which will reach a height of 3mm on the cork. After 24 hours remove the stoppers and measure the maximum height reached by the solution. Measurement should be rounded off to the nearest .5mm.

Acceptable Values: 3mm - and not to exceed disk

Torsion will be measured in accordance to NP2803 A Method - whereby the cork is submitted to torsion at a 100o/min rate - twisting until the cork cracks. Measurement will be in terms of shear strength as measured by the formula 16T/pd3 where d is the diameter of the cork and T is the momentum calculated as T=FxBxsin(a/2) where a is the torsion angle.

Acceptable Values Min 7 daN/cm2 

Treated or Untreated stoppers are marked and placed in a an ethanolic solution containing 10% alcohol by volume adjusted to 3.5ph. Vigorously agitate for 20 minutes. Filter solution using a .45 micron membrane. After drying weigh any residuals in a ration of mg/cork.

Acceptable Values < 2.0 mg per cork

Binding agents will be prepared in compliance with USFDA regulations as seen in Title 21 CFR 175 Subpart B [175.105].

Agglomerate corks must contain a minimum 80% natural cork as measured by weight. Methodology for compliance is being researched.