THE NATURE OF CORKS
Natural wine corks are one of the most remarkable products of nature, and have played a critical role in the development of the premium modern wine world.The incredible properties of natural cork are primarily the result of cork's unique structure.
The bark of the cork oak tree is composed of tiny cells, each a 14-sided polyhedron, with the intercell space entirely filled with air. There are approximately 40 million of these cells in a single cubic centimeter of cork bark. These cells give cork an unmatched ability to seal a wine bottle. The cellular membranes are very flexible, making the cork both elastic and compressible. These cell walls are impermeable to both liquids and gasses. When released from pressure, the cork quickly recovers its original shape and volume.
This allows the cork to quickly conform to a bottle neck and seal it tightly against the primary enemy of fine wine--air. Equally important, the natural cork maintains its flexibility for decades, making the seal long-lived, and making removal a simple process. This tremendous longevity helps the cork protect fine wines for decades.
The use of natural corks to seal wine bottles in the late 1600's and early 1700's encouraged winemakers to begin making richer, more powerful wines which would improve with age for decades, protected by natural corks. Today the greatest wines in the world owe their style and fame to the use of corks to seal their legendary (and costly) bottles. The sound and feel of a natural cork being pulled from the bottle signals the start of one of life's greatest pleasures -- good friends, good food, and a great bottle of wine.
How can one material have so many unique properties? The story begins in the forest. QUERCUS SUBER Cork is the bark of the cork oak tree (Quercus suber) which grows only in specific regions of the Western Mediterranean. Attempts to grow this tree in other regions of the world with similar climates have not succeeded.
The cork oak requires a great deal of sunlight and the unusual combination of low rainfall and somewhat high humidity. The quality and thickness of the bark of the cork oak varies according to these growing conditions. The fact that corks are made from bark harvested from living trees has encouraged European environmentalists to encourage the use of cork over other, less natural alternatives. Cork forests not only reduce the need for other polluting industries, they also help clean the air of the pollutants caused by these industries.
In fact, the cork forests are among the most regulated agriculture in the world--the forests are considered national treasures, and every step is carefully documented and regulated for the government.
The largest cork producing country is Portugal, followed by other Mediterranean countries such as Spain, Algeria, Italy, France, and Morocco. Portugal produces nearly 50% of the cork in the world, and the quality of its cork makes the country a leader in both quantity and quality.
THE CORK FOREST
Traditionally, cork forests have been wild--left to themselves and harvested when appropriate. But recent investments in the industry have led to developments in the forest--including genetic selection of better trees. The resulting young trees are straighter than usual, and they are growing much quicker. Dr. Tom Leydig is heading a research program determining the genetic variation of cork trees in the Mediterranean, so that more successful cross breeding can be done.
These new trees will get their first harvest after only fifteen years, rather than the usual 25 or more, and the straight trunks will allow more profitable harvests, as well. These new plantings have invigorated the cork industry--the average age of corks trees in Portugal is under 80 years old, while the tree will continue to produce for 200 years or more.
In Portugal, the revolution of 1974 had a significant impact on cork agriculture. In the days after the revolution, the forests were broken up into small parcels, and the result was an uneconomic scale of farming. It was simply not cost effective to bring in the farm equipment to control the cover crops which steal water and nutrients from the trees. Each year, more forests are getting the attention and care that they need to produce great cork--clean fields, healthy, carefully pruned trees.
THE HARVEST
Cork trees are harvested in the summer, every nine or ten years, after they reach 25 centimeters in diameter. This harvesting process in very strictly regulated by the government.
Harvesting a cork oak is very skilled labor. Specialized axes are used to cut a ring around the tree at the top of the trunk, and then make one vertical slice down the trunk. The axe is then used as a lever--it is inserted into the vertical cut and used to gently pry the cork off the tree. The cork is peeled off in large panels and stacked in the orest. Obviously, great care is taken to avoid cutting into the cambium layer of the tree, which is still alive.
There is a significant difference between first harvest, or virgin, cork, and third harvest. The virgin cork is rough, crumbly, and can only be used for cork board, insulation, gaskets, shoe soles, etc. By the third harvest, the cork is beautiful, clear bark that will make great wine corks. After the cork is harvested, it is left to age for a period of months to allow the moisture content to stabilize.
While the cork is aging in the forest, the cork producers come to the forest to inspect it, select their lots, and negotiate the price.
CORK PRODUCTION
All cork must be boiled before it is worked, to make it more pliable, and to fully expand the lenticels. These cells are collapsed and wrinkled before boiling, but after boiling, the air in the cells expands, and creates a very tight, uniform cell structure that looks like a honeycomb.Some producers are now using a giant autoclave to boil the cork. This has a number of advantages: it is much quicker than boiling, it allows the moisture content to be very carefully controlled, so that the cork may be worked very soon after, and the gases from the autoclave can be analyzed for quality control studies.
All good producers analyze their incoming cork for quality control purposes-- another example of how the cork industry is making an investment in quality. This investment is critical. Demand for top quality cork by such organizations as the Cork Quality Council in California has encouraged a focus on quality. In fact, top cork suppliers will only work with those companies investing in quality and new equipment and techniques.
When the cork has been boiled and dried to 20% moisture content, it is ready to work. It is graded by a worker who slices the cork to expose a clean surface. Only the very best cork wood will become wine stoppers. Such wood has very few defects, and is very consistent in color, texture, and density.
Following the grading process, the cork is sliced into narrow strips as wide as a wine cork is long, from which the corks will be punched. The very best corks will be more than 50 millimeters long. Each cork shows the growth rings of the tree running vertically through the cork.
The punching is very technical work. While machines have been used, they are incapable of making the critical judgment calls that veteran punchers make so well.
After punching, the extra material will be used for champagne cork tops, gaskets, cork flooring--even insulation on NASA's space shuttle.
CORK WASHING
Once punched, the corks are ready for washing.
The latest washing systems use rolling cylinders to spin the corks in the liquid. Huge tanks hold carefully monitored chemicals, which are pressure washed into the corks and then rinsed by a similar computer controlled process.
This provides better interaction between the corks and the washing liquids, better quality control, and more accurate testing. This machinery is a major step forward. There are now a variety of washes--the popular chlorine wash, hydrogen peroxide, and sulfur dioxide wash as well. Each is effective, as long as it is done properly.
Much of the research concerning washes is done at CTCOR, the cork industry's technical laboratory outside Porto. Here they study virtually every factor in cork production, and provide research and analysis to the 150 or so international members which sponsor it. Some members of California's CQC are also members of CTCOR.
In addition to the new equipment and washing techniques, top producers are placing great emphasis on clean, professional facilities. Moisture control following washing is a critical element in this effort.
Today, top producers are using a combination of techniques to quickly dry the corks. First a conveyor belt furnace dries off any surface moisture within minutes of the washing. Then a temperature and humidity controlled room dehydrates them even further.
The moisture is lowered to 8%, where no mold can grow, and kept there for the rest of the life of the cork. After the corks are washed and dried, they are visually graded yet again. One procedure is via a team of very highly trained women, who inspect a large lot of corks and quickly judge them for visual quality.
The latest system involves optical sensors programmed by computer to select corks on the basis of a number of factors. And while these are very fast and efficient, most cork producers will tell you that they still prefer to use the women for a final check-- because they are more accurate than the computers.
Corks are graded VISUALLY-they are graded by what they look like, not what they do. Very expensive corks are beautiful and nearly perfect, but even less expensive corks will seal a bottle effectively. One of the most complicated subjects in the cork industry is the concept of grading. Because they are natural products, it is impossible to perfectly classify corks--some people may prefer one type, while others look for something else. To eliminate some of the confusion surrounding cork grading, the Cork Quality Council has developed some basic visual grading standards for the California wine industry. The new standards use specific and measurable visual criteria to describe each grade.
Once the corks are washed, dried, and graded, they are almost ready for use. They receive a final coating of paraffin and silicon. This will help them seal the bottle and be removed easily.
QUALITY CONTROL
Because of its dominant position, the Portuguese cork industry has a huge impact on the cork industry as a whole. In the last twenty years, the Portuguese cork industry has been in transition, making changes to improve both the quality and consistency of its corks from the trees in the forest to the finished product in the wine bottle.
Of course, many of these developments have been made possible by Portugal's entry into the European Community. European companies are investing in the future of cork--an environmentally sound industry which adds to the quality of life in their community.
There are extensive quality control laboratories at cork producers in Portugal, and they provide a great deal of data to the industry. By comparing the results they get with the results members of the California-based Cork Quality Council,transport problems can be easily identified.
THE CQC'S ROLE IN QUALITY
The Cork Quality Council is an organization of seven cork suppliers who work together to improve the quality and consistency of corks in America, while educating the wine industry to improve bottling techniques and the proper use of those corks.
The CQC is currently involved in a series of research projects concerning cork coatings, bottling techniques, and bottle variation. In addition, they organize educational "round-table" seminars for the wine industry, and have developed a infomational materials about corks. These are important, because there is more mis-information about corks than about any other factor in winemaking.
The members of the Cork Quality Council must track all incoming corks to mil spec standards.The organization has
provided the wine industry with a series of recommended bottling procedures to eliminate problems at the winery. And the CQC has developed new standardized visual grading classifications to help wineries understand corks better.
The Cork Quality Council works with top wineries on these projects for two important reasons. The first is to make sure that the final recommendations are applicable to the state of the industry today. And second, these wineries have excellent quality control procedures, and can document their success.
Since these cooperating wineries have very few problems with their corks, they serve as an excellent example to any winery which is having trouble.
The CQC is currently working with Dr. Ken Fugelsang of Fresno State on a series of studies to determine the best way to treat corks, and the best way to use them. The research has already pointed to a number of new directions for wine and cork quality.
Recent research indicates that as wineries reduce the use of sulfur dioxide, they may run the risk of more wine spoilage.
>> Dr. Fugelsang has created moldy, musty aromas in wines without any contact with corks. Low levels of hydrogen sulfide can interact with ethyl acetate to create compounds easily confused with cork taint.
>> Wines with lower amounts of sulfur dioxide, and wines with higher pH are much more likely to develop cork taint in the bottle. One wine, with a pH of 3.15, and SO2 of 38 ppm, developed no identifiable cork taint, even when sealed with mold infested corks!
Dr. Fugelsang, is also working with a number of wineries and members of the CQC to develop a series of Quality Control Procedures which will help wineries understand the issues at stake.
CORK TAINT
So called "cork taint." is 2,4,6 Trichloroanisole, or TCA, and is often mis-identified and blamed for
any flaw in wine. TCA smells like mildewed paper, and it is present in coffee, chocolate, raisins, beer, bottled water, and even soft drink cans. It is present, in very small percentages (1% more or less) in corks.
TCA is created when molds metabolize trichlorophenols. Tricholorphelols are omnipresent, due to their role as disinfectants throughout the world. The key to eliminating TCA is to limit the presence of mold.
The measures discussed above have made a huge impact on the incidence of TCA in corks, and all of the above industries are working to eliminate it entirely. Ironically, because it has been found in both beer, with a crown cap, and bottled water, in a plastic container, the solution will be something that improves ALL foods and beverages, not just wine corks.
There are currently a number of different research projects concerning TCA in progress, from bottling techniques to microbiology, to coating technologies, to pull strength tests and leakage analysis.
And while each of these indicates even more directions for research, they have all shown one thing: compared to the alternatives, corks continue to be the best choice for sealing bottles of wine. Which is why the best wineries in the world will continue to use natural corks for their finest wines.
COMMON MYTHS AND ERRORS
>> Occasionally, there is a news report of the demise of the cork forests of Europe. This is simply not true. There is one small section of a single cork forest in Portugal which is being affected by industrial pollution nearby. The effects of this pollution are limited to approximately ten percent of the trees in this one forest, or less than one percent of all cork trees in Portugal. The pollution is being controlled to eliminate the problem.
Perhaps one source of this curious falsehood is a British wine magazine which printed a story concerned a nematode called "Primiaprilis Americensis" (First of April in America) which was attacking the cork tree roots. The humor was well intentioned, but some people may not have understood it!
>> Despite illustrations in the children' story Fernando the Bull, corks do not grow on trees like almonds or olives.
>> Nor are the cork tree harmed or killed in order to harvest the cork. The trees can live for hundreds of years, and will continue to produce cork for that period.
>> There is also an astonishing rumor that cork production is failing to keep up with the increasing demands of the wine industry. In fact, wine consumption is down in every major country, and the demand for corks has shown an equivalent drop.
>> A recent American Society of Enology and Viticulture presentation noted that if cork bark is not boiled immediately after harvest with chlorine, it will rot in a matter of weeks. This is obviously not true. Cork fishing floats continue to float for centuries, and corks have sealed the greatest wines in the world for decades.
>> The same ASEV presentation also noted that the cork SLABS were washed in chlorine. In fact, only the punched corks themselves are ever washed.
CORK REFERENCE MANUAL
To improve the use of corks by the wine industry, the Cork Quality Council has developed the following reference materials.
These materials are intended to be used as guidelines, and there may will be reasons to adapt these procedures to the specific equipment and goals of the winery.
Nevertheless, we strongly encourage wineries to use these guidelines as a foundation upon which to build a bottling and quality control manual.
CORK WASHING STANDARDS
CTCOR, the Cork Technology Center of Portugal, has developed the following recommended guidelines for the processing of corks. While these are general guidelines, the CTCOR laboratory has spent considerable time researching these processes and analyzing the results.
The Cork Quality Council, recognizing CTCOR's leadership in this field, has provided these general guidelines as a part of our on-going educational efforts on behalf of cork and the wine industry.
TRADITIONAL CHLORINE WASH
1. Begin with a tank (without dust) with an aqueous solution super saturated with calcium hypochlorite. The end result should be a final bath with a maximum total of 30 grams per liter of free chlorine. Submerse the corks in this bath, agitating them for approximately two minutes.
2. Allow the corks to remain at ambient temperature for a time not to exceed two hours.
3. Repeat steps 1 and 2 ONE or a maximum of TWO times.
4. Immerse the corks in a bath of clean water, agitating them for two minutes.
5. Submerse the corks in an aqueous solution of oxalic acid at 6 to 8 grams per liter, agitating them for a period of two minutes.
6. Immediately centrifuge the corks, and then dry them until the moisture level becomes stabilized at a humidity which should be between 6% and 8%.
HYDROGEN PEROXIDE (H2O2) WASH
1. Submerse the corks in an aqueous solution
containing 10% hydrogen peroxide and 3% (by volume) of commercial ammonia, agitating the corks for approximately five minutes.
2. After removing the corks from this bath, allow the corks to remain for thirty minutes at ambient temperature.
3. Immerse the corks in clean water for two minutes, agitating them.
4. Submerse the corks in a solution of 1% citric acid by weight, agitating them for approximately five minutes.
5. Immediately centrifuge the corks, and then dry them until the moisture level becomes stabilized at a humidity which should be between 6% and 8%.
POTASSIUM METABISULFITE (SO2) WASH
1. Submerse the corks in an aqueous solution of potassium metabisulfite (1% by weight) for approximately five minutes.
2. Immediately centrifuge the corks, and then dry them until the moisture level becomes stabilized at a humidity which should be between 6% and 8%.
SULFAMIC ACID WASH
1. Submerse the corks in an aqueous solution of sulfamic acid (2% by weight), agitating the mixture for approximately five minutes.
2. Allow the corks to remain at ambient temperature for 10 minutes after removing them from this bath.
3. Immerse the corks in clean water for two minutes, agitating them.
4. Immediately centrifuge the corks, and then dry them until the moisture level becomes stabilized at a humidity which should be between 6% and 8%.
CORK QUALITY COUNCIL VISUAL GRADING STANDARDS
The seven members of the Cork Quality Council have developed standardized visual grading criteria for the corks they supply to the wine industry. The CQC has developed these standardized visual grading criteria to provide a consistent terminology for the visual aspects of the corks sold in the United States.
This follows years of confusion between different companies and even different countries concerning the terminology used for the visual grading of corks. The new visual grading standards will be used by all seven members of the Cork Quality Council, and are designed to be used by wineries to better understand the individual lots of cork they purchase.
However, there are three key points which must be understood by those who use these new criteria to describe the visual aspects of the corks they purchase from the members of the CQC.
>> Corks are a natural product. As such, the visual aspect will vary from cork to cork and from lot to lot. These new visual grades are designed to describe a range of corks of similar visual appearance. Because of the natural variation between individual lots of cork, all corks of a single visual grade will not be identical in every characteristic.
>> The CQC visual grades describe the physical appearance of the cork, rather than the structural integrity of the cork. While there is some correlation between the visual aspect of a cork and its structural integrity, there is no direct mathematical relationship between these two elements of cork quality.
>> Every defined lot of corks will inevitably contain a mixture of corks of more than one visual grade.
>> Because there will be some variation within a single visual grade of cork, the CQC strongly recommends the use of samples of appropriate size when evaluating lots of corks. The CQC suggests the use of Mil Spec Standards to determine sample size for an individual lot of corks.
CQC GRADE "A"
These are corks with top quality visual appearance --excellent surfaces, with no major visual flaws and few small ones. As such, there should be:
>> No holes or pores which exceed 2mm.
>> No cracks originating at the ends which exceed 11% of cork length.
>> No cracks in the body of the cork to exceed 18% of cork length.
>> All cracks must be tight and not open.
>> No horizontal cracks.
>> No worm holes, hardwood, belly spots, or greenwood.
>> Several narrow and shallow lenticels are acceptable if they are free of dust and particles.
CQC GRADE "B"
These are corks of good visual appearance with no major visual flaws and with surface visual flaws of no depth or substance. In these corks there should be:
>> No holes or pores which exceed 5mm.
>> No cracks originating at the ends which exceed 18% of cork length.
>> No cracks in the body of the cork to exceed 25% of cork length.
>> All cracks must be tight and not open.
>> Lenticels and horizontal cracks on body must not open up when the ends of the cork are bent.
>> No greenwood, no angled or deformed corks.
>> Very small chips and lateral worm activity in the middle of the body of the cork may be acceptable.
>> Lenticels at ends must not be wide or deep and should be free of dust and particles CQC GRADE "C"
These are corks of
average visual appearance
with one or more major
visual flaws which will
be of cosmetic nature
only. Thus they may be
esthetically unappealing, but functional. In these corks there should be:
>> No cracks, channels, hardwood, or belly spots which exceed 55% of cork length.
>> Lenticels and horizontal cracks on body may open up when the ends of the cork are bent.
>> Greenwood to 55% of cork length is acceptable unless severe depth or width.
>> Large chips are acceptable
>> No worm activity from end to side which exceed 55% of cork length.
>> No dry years which exceed 55% of cork length.
>> There may be heavy, but not continuous, porosity.
CQC GRADE "D"
These are corks of poor visual appearance with major visual flaws which will not cause a malfunction in the performance of the cork. In these corks there should be:
>> No cracks, channels, hardwood, or belly spots which exceed 75% of cork length.
>> Lenticels and horizontal cracks on body may open up when the ends of the cork are bent.
>> Greenwood to 75% of cork length is acceptable, or less if of severe depth or width.
>> Large chips are acceptable
>> No worm activity which exceeds 75% of cork length.
>> No dry years to exceed 75% of cork length.
>> There may be heavy, continuous, porosity.
>> There may be badly stained corks.
>> There may be corks of incorrect size.
CQC GRADE "E"
These are corks which do not meet the standards for Grades A-D.
CORK DEFECT DEFINITIONS
Belly Spot.--Surface depression - caused by the dense inner surface of the cork strip from which the cork is cut.
Channels.--A groove running along the surface of the cork - caused by cutting corks too close together.
Chips.--Irregular pieces missing from the cork surface usually on or near the ends - caused by processing damage due to dry or brittle cork wood or faulty corker jaws.
Cracks.--A crack or fissure in the surface of the cork - generally caused by the wood being too dry or brittle. This can cause chips during processing.
Dry Years.--Narrow woody growth rings - caused by a lack of rain during the growth year.
Greenwood.--Undulations in the surface of the cork - caused by moisture related conditions.
Hard Wood.--Hard rough areas on the surface of the cork - caused by cutting the cork too close to the bark surface.
Lenticells.--The cell structure of the cork - it runs horizontally in cork closures. Each lenticell is a 14 sided polyhedron with the intercell space entirely filled with a gaseous mixture almost identical to air. 1 cubic centimeter of cork wood contains about 40 million individual cells.
Pores.--Holes or fissures or soft pith-like tubes/canals in the lenticell structure.
Porosity.--High density pore activity.
Worm Holes.--Holes in the cork caused by worms forming canals from their entrance in the cork to their exit from it.
CORK QUALITY COUNCIL INCOMING QUALITY CONTROL FOR CORKS(REVISED APRIL 1993)
I. Sampling Plan:
Individual lots of corks should be sampled using U.S. Government Military Standard 105-D plan. From the sample taken, smaller sub-samples are randomly selected to undertake the following quality tests.
II.
Acceptance/Rejection:
Guidelines for acceptance and rejection to follow US, Government Military Standards 105-D Inspection Plan (reduced inspection), at the various acceptance levels as indicated per test below.
III. Test Procedures:
A. Sensory Test:
1. Sniff Test: The number of corks to be tested will be in accordance with Mil Std 105-D:
2. Six corks from each bale taken as per IIIA1, 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 a minimum, will be in accordance with Mil Std
105-D (reduced). Individual corks are classified into pre-
determined 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 Moisture Register Co. or Aqua-Boy 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:
1. Corks are to be placed in a drying area which is physically separate from the storage area for accepted corks.
2. 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 Moisture Register Co. or Aqua-Boy cork moisture instrument will be used. Moisture level must be below 7.5% average, with a tolerance per AQL 4.0.
3. 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 ISO 3863, and acceptance at Military Standards 105-D.
Diameter: as specified (+/- 0.50 mm) AQL = 1.5
Length: as specified (+/- 1.00 mm) AQL = 4.0
E. Residual Oxidants:
One cork from each bale taken as per paragraph IIIA1 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
IV. A lot is defined as a particular wood quality, size and wash from an individual supplier in a single shipment.
V. Permanent records of the quality control tests for each lot will be kept for a period of at least five years.
OUTGOING QUALITY CONTROL FOR STILL WINE CORKS
I. Test 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 same procedure as Incoming Cork QC. Prepared batches should have an average moisture range of 5% to 8%.
II. 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. Permanent records of the quality control tests for each lot will be kept for a period of at least five years.
IV. Every reasonable effort will be made to ensure the pristine character of the corks is preserved while in processing at members' facilities in this country.
CORK QUALITY COUNCIL RECOMMENDED CORKING PRACTICES
I. Corker Jaw Type:
A. The 4 segment sliding jaw type cork compression system is recommended. Roller or iris type jaws tend to cause wrinkles in the cork which can cause leaking.
II. Corker Maintenance to Ensure:
A. Corking machines are maintained to manufacturers recommended standards at all times.
B. Smooth action in compression stage.
C. No nicks or other damage to the jaw segments.
D. Good alignment and seal of bottle neck in centering bell.
E. Properly centered plunger.
F. Daily cleaning and sanitation of cork handling surfaces; i.e. hopper, feed tube, orienter, and jaws.
G. A 24mm cork should not be compressed to less than 16mm.
III. Cork Handling and Storage:
A. Do not open plastic cork bags until immediately before loading corks into the loading machine. No bags containing corks should be left open for any reason.
B. Corks recovered from the corking machine after the bottling is completed should be returned to the plastic bag or another closable container, "dosed" with sulfur dioxide gas (vapor) and sealed tightly.
C. Corks should be stored in a cool dry location, not in a bottling room, barrel storage area, or chemical storage area. The temperature should be 55 to 70 degrees Fahrenheit and the humidity 50 to 70 percent.
IV. Moisture Content:
A. New shipments of cork, as well as corks which have been stored for extended periods of time, should be checked for moisture content before use. Corks below 5% average moisture level should be discarded or returned to the supplier for re-hydration and sterile packaging.
B. Corks with an average moisture content of over 8% should be regarded with suspicion as such a moisture level could support mold growth.
V. Internal Bottle Pressure:
A. Wine temperature should be between 60-70 degrees F. If lower temperatures are used then the fill point should be adjusted down to compensate for expansion in the bottle when room temperature is reached. (Be sure to maintain legal fill volume.)
B. If the fill point is too high, less vacuum can be achieved.
C. The vacuum system should be well controlled and maintained. Gauges which continuously display vacuum status at the corking head and frequent (each 1/2 hour) online QC of corked bottles (pierce test) are highly recommended.
D. Bottles should remain upright for 24 hours after corking.It is recommended that the above elements be combined to produce a net effect of no more than 3 psi internal bottle pressure at 68 degrees F.
COMMON WINE SPOILAGES
2,4,6, Trichloroanisole, also called TCA or "cork taint," is often mis- identified. It has a distinctive "mildew" that is not easily forgotten once it has been experienced.
This unpleasant odor has been found in bottled water, wine bottled in screw caps, beer, and even raisins--none of which have contact with corks. Thus it is more correct use the term TCA to describe it.
Laboratory analysis by top wineries indicates that less than 1% of their wine is affected by TCA. Unfortunately, much of what others call "cork taint" in wine is not accurately identified. Below are a number of other types of wine spoilage and their characteristics, which can be found in wine.
Oxidation--a flat or caramel aroma. A flat, cardboard-like taste inthe wine, sometimes, but not always accompanied by a browning of the color of the wine. Caused by interaction of oxygen with wine.
Hydrogen Sulfide--a rotten egg smell. Often due to lack of attention in winemaking.
Volatile Acidity--a sharp vinegar-like or nail polish smell. May be associated with acetic acid and bacterial infection.
Sulfur Dioxide--the odor of freshly burnt matches. Used as a anti-oxidant in wines. Caused by overuse of sulfites.
Brettanomyces--smell associated with cheese or wet horses. Normally caused by spoilage yeast in barrels.
Mercaptans--aroma is reminiscent of bad onions, cooked cabbage or burnt tires. Odors which result from bound hydrogen sulfide. Caused by bacterial spoilage, usually originating in the barrels.
Quaiacol--a musty, vegetal smell. A very rare contamination from barrels or corks.
Geosmin--a smell of beets. Earthy. Extremely rare, it may originate in cork or barrel.
Geraniol--smells like geraniums or lemon grass. Increasingly rare by-product of potassium sorbate. Used as a preservative in wine.
Deccara--a burnt sugar smell. The result of a poorly managed fermentation.
In addition, certain wines may be:
Overly tannic--a dry, puckering feel in the mouth. Tannin is a natural component of the grape itself.
Overly alcoholic--a hot feel in the mouth. Caused by fermenting grapes with high amounts of sugar. Overly acidic--a sharp taste along the sides of the mouth--cause by unripe grapes or acidification.
WINE CORKS: WHAT ARE THE ALTERNATIVES?
Corks and corkpullers are an integral part of wine--and have been for nearly 300 years. But every so often word comes of a new and improved seal for a wine bottle.
Here is a simple analysis, comparing the advantages with the disadvantages of each.
AGGLOMERATE CORKS:
These are made by binding together smaller pieces of cork into a single closure. While less expensive than a true cork, they suffer from virtually every comparison-- they are not as attractive, they may not last as long as true corks, and they do not have the same resilience as cork--a critical element in making a perfect seal of the bottle.
Nevertheless, some wineries are happy with these agglomerate corks for their less expensive wines designed to be drunk in the near future.
COLMATED CORKS:
These are usually lower grade corks which are treated with a combination of adhesive and cork dust to fill the fissures and holes in the corks. They offer a lower cost alternative to attractive corks, but do not offer equal appearance, performance, or image.
THE SCREW CAP:
Often mentioned as the epitome of cheap wine, these closure do carry a negative connotation in the marketplace. They are very inexpensive, but require a special threaded bottle.
Unfortunately, there are no long term studies to indicate how well these closures hold up under the long term storage planned for fine wines--there are also concerns about oxygen transpiration across the relatively narrow surface of the plastic seal.
For the liner of a screw cap to seal effectively, it must contain a high percentage of plasticine, which imparts flavor. Lower percentages do not impart flavor, but will not seal as well. Quality control is necessary to monitor this variable. Screw caps are easier to open and close than corks, but there are concerns about the bottling process, specifically the ability to draw a vacuum in the headspace to remove oxygen.
THE BOTTLE (CROWN) CAP:
This is very similar to the screw cap in every way--except that there may be even less evidence in favor of long term aging potential. They are even less expensive than screw caps, and also require a special bottle. TCA from cardboard case boxes can be transmitted through the plastic liner of crown caps into the liquid.
THE SYNTHETIC CORK:
Made from a plastic, this closure resembles cork, but is easily identified on close inspection. It does not offer the same recovery from compression, which means that bottling lines must leave bottles upright for a time before they can trust the seal. A number of other concerns about these stoppers have been noted in the wine media.
U.S. MILITARY SPECIFICATION STANDARDS 105D
TOTAL CORKS # BALES TO SAMPLE # CORKS PER BALE
50,000 2 125
100,000 3 125
200,000 5 125
400,000 8 125
600,000 13 125
800,000 13 125
1,000,000 20 125