FAQ Natural corks

1. What is it about natural cork that makes it a great stopper for your bottle of wine? 

Wine and natural cork are both natural, organic products which go extremely well together.

Natural cork is a renewable resource and therefore ecologically and environmentally friendly.

Its use is an expression of wine culture and evidence of the high quality of the wine. Hence, 90% of all customers expect a natural cork if they open a bottle of wine. 

Natural cork is a unique material and has been used through the ages as a  stopper for wine and champagne bottles. Even now, no one has succeeded in reproducing exactly this natural product with its important properties…low gas porosity and high elasticity. 

2. What are three of the biggest advantages of a natural cork compared with other bottle stoppers? 

The natural cork comes 100% from a renewable resource raw material. It is gas-permeable as well as extremely elastic due to its cellular structure (approx.
40 mio. cells / cm3). After the product is used it is fully recycleable for other uses, and biodegradable. 

3. Are all Natural Corks the same? 

No. Corks are sorted in up to six different grading procedures. The quality is dependant on well-chosen raw material and other production or refining procedures of the individual manufacturer. One of the important criteria for the quality is the quantity and location of the pores on the surface: High-quality Natural Corks are almost flawless on the surface, while the middle and lower grades of corks show areas where the pores increase in number visibly. 

Furthermore, today corks differ in relation to their area of application: whether they are to be used for still wine, sparkling wine, champagne or spirits. 

4. Are there also other "cork types" besides Natural Corks? 

Yes, in particular Technical Corks (stoppers with one or two solid discs on the ends with milled cork particles and adhesive between, which we call Twinline®), Colmated corks (see question 7), and Agglomerate Corks (stoppers made up of milled particles with adhesive, without the solid disks). 

5. What is a technical cork?

Called by GUELTIG CORK a Twinline® Cork (also called a "twintop", a "1 + 1" and a "bi-disk" among other names), the body is composed of  Agglomerate particles with a solid disk from Natural Cork at the ends. The Technical Corks are made up of the same product as the in the Champagne Corks. The differences lie in the sizes as well as the position of the cork disc: with champagne cork 2 disks are used on one end, with the Twinline® Cork stopper, one disk is used on each of the ends. 

6. What are the advantages of Twinline® Technical Cork compared with Natural Cork? 

Twinline® due to their technical-industrial manufacture process are of a very homogeneous quality. By the Agglomerate, Twinline® corks are very air tight what covers his relatives, the champagne cork, steadily. Agglomerat and cork discs are submitted before the completion of their processing by compressed steam by which removes a maximim amount of contamination and off aromas. Twinline® have proven itself with GUELTIG's customers for many years as the price-conscious alternative with high sensory neutrality. 

7. What is a Colmated Cork? 

This product was developed originally in France and this is also traditionally where it has become the most popularly used. 

Colmated Corks are produced usually from cork material with a lower quality or grade. These corks mostly have bigger pores and possibly also other visual defects. After the corks are punched, the corks are coated with a mixture of "cork flour" and paste and are coated to improve and raise the visual quality so that they can be used as a wine cork. 

8. What is today's actual worldwide cork demand? 

The EU has placed the cork oak (lat. quercus suber), due to its unique ecological properties, under their protection. For example, unproductive or unhealthy trees (usually after approximately 200 to 300 years) must be replaced with cork oaks again. 

In order to insure the availability of Natural Cork, the forests are also protected furthermore by constant natural re-forestation. The area of cultivation has increased annually about 2-3%, to approximately 1.6 M acres. 

9. How many corks can be produced from a metric ton of corkwood? 

Approximately 50,000-60,000 corks of normal size are produced from it. 

10. Is it true that pesticides are used in the cork oaks forests? 

No, this statement is wrong, in spite of it being repeated over and over.  

11. Is it correct that the cork oaks are damaged by the harvesting procedures? 

If the harvest is carried out expertly and at the correct time, which is controlled by the goverment and the forest owners, the tree is not damaged and can reach a proud age of from more than 200 - to 300 years.           

12. Is it true that cork oaks are fertilized? 

No. The harvesting  of the cork oaks is specified by law and supervised after at least nine years of growth. Therefore, an acceleration of the growth is not necessary.  Fertilization is not practicable, would be senseless ecologically and, besides, it would be uneconomical. 

13. What do the cork manufacturers do to improve the quality of Natural Cork? 

Today, the industry puts the biggest emphasis on very much a high degree of quality with the purchasing department of the raw material, in the production of the raw corks, the refining and the quality assurance of the finished goods. Long-standing experience pairs off here with the application of the newest technologies like the Gaschromatograph (GC/MS) and newest knowledge from research and development. One of the most important goals is the complete elimination of smell-influencing and taste-influencing substances like TCA. 

14. Has the quality of Natural Cork become worse and worse over the years? 

The quality of natural cork remains at least stable with cork manufacturers and cork suppliers with effective quality assurance programs. Our purpose at GUELTIG CORK is to increase the quality according to the requirements of the market continuously, and at all times. 

15. Why is a quality Natural Cork becoming so expensive?

The cork wood, especially the clean raw material, has become expensive, especially during the last ten years.  The amount of manual labor necessary with the production of natural cork is a significant factor. Also, current adaptations to the wage level in the EU and the urgently necessary measures to increase the Quality Assurance have effects on the market prices for Natural Cork. Likewise, costs increasing from additional Quality Assurance measures and Quality Assurance machines have become more and more important, as for example Gaschromatograph testing.

16. Does it matter from which manufacturer / cork producer I purchase my corks? 

Yes. As in all other production businesses, every cork manufacturer and cork producer has its own methods and production procedures. At GUELTIG CORK laboratory, only the newest laboratory technology is used for inspection and testing purposes.  Testing procedures cover the entire production process of our corks. All procedures and materials that are used at GUELTIG CORK in the production of our products fulfill the International Standards (FDA, EU guidelines) and regulations for food utility items (LMBG). 

With approximately 20% of the staff here at GUELTIG CORK occupied with Quality Assurance (QA) as well as Research and Development (R&D), GULTIG CORK invests in the areas of approximately 350,000 EUR per year. 

17. GUELTIG CORK is certified by HACCP. What significance does this have for me as a customer? 

HACCP is the most austere standard in the production of food.

GUELTIG CORK continues to be the first and only cork supplier in Germany who offers this certificate of validity. 

We have undergone voluntarily this certification to offer the greatest possible product security, to minimize possible health risks and to mark themselves as a supplier of companies Certified to IFS.  

More and more bulk buyers of wine and other drinks are requiring from their suppliers of packaging, etc. suitable QA Systems and Certifications.  

18. Is GUELTIG CORK / Heilbronn a manufacturer of cork or merely an importer? 

We are a manufacturer! Individual production steps are partially carried out by our pre-suppliers for cost reasons, but only after our technical requirements have been met. Our own staff is on site in Portugal checking the processing of our suppliers on a constant basis, observing and testing to insure the implementation of these technical guidelines (QTLB) during and at the end of the manufacture. GUELTIG CORK does not operate any differently than the automobile industry such as Daimler, which buys more than 70% of it's parts from suppliers, and then assembles them. 

19. Why should I purchase my corks from GUELTIG CORK / Heilbronn? 

The reasons for this are many and varied. We would be happy to have one of our Sales Agents explain this to you in a personal discussion. Please see "agents", you will find them at company - worldwide.

20. Are their any actual guarantees that by purchasing from a prestigious cork manufacturer, that the corks can always be used without any problems? 

GUELTIG CORK / Heilbronn guarantees their customers a high grade and quality cork up to the time of delivery. After the receipt of the product, the customer himself is responsible for the appropriate storage and use of the corks.  

GUELTIG CORK / Heilbronn has numerous experts available for their customers who assist the customers to avoid mistakes with storage and processing. You can always call them by phone or contact us at our web site at contact. 

21. What are the important factors in the storage of cork? 

Natural corks should be stored in separate rooms from other production, which are well ventilated, free from odors and normally within a temperature range of  18 / 20 °C (64,4 / 68 °F).

With too cool storage (<15°C / <59°F), Natural Corks become hard and fragile. This can affect negatively the processing and later sealing. 

With too warm storage (> 15°C / <59°F), Natural Corks become too soft. This can lead to the pushing out of the corks from the bottle mouth. 

It is important that the corks are always stored 24 hours before using in room temperature, especially before bottling in unfavorable temperature conditions. 

22. What are the causes for leaking bottles? 

There are different causes that often appear also in combination as:

Irregularities of the bottle mouth

damages of the cork by the cork jaws

natural damages of the cork, as for example worm holes,

that can also damage the cork and cause leakage problems.  

23. What is better: standing or recumbent storage of the wine bottles? 

To avoid pressure-conditioned runners, a standing storage of 24 hours should be kept in the ideal case after corking. With available and functioning pressure-reducing measures (CO2 overlapping, vacuum equipment) a standing storage of 5 minutes is enough. Then the bottles can be stored easily standing (for a maximum of two years) or recumbent. 

24. What is a "cork taint"? 

"Cork taint" has become a collective name of off aromas which are the same as 2,4.6 TCA in taste or very similar. 

"Cork taint" is therefore a confusing and somewhat false name. Cork in itself does not influence the wine negatively, however, cork can be contaminated with 2,4.6 TCA -a substance, which is responsible worldwide for the infection of numerous foods (see also question 25).  

25. Does the cork taste originate in the wine only from the cork? 

"Real" cork taint (TCA) originates, in principle, only from the cork or its treatment and processing. However, there are also other off aromas, which does not originate from the cork, but are often mistakenly called cork taint (see question 24). Thus TCA was already found in mineral water, wine bottles with screw cap, beer, lemonades, pre-packaged food and even in chicken eggs. Causes of such contamination can be: 

  • Contamination of oak barrels
  • Contamination of cellar machines (filter, pumps), filling layouts
  • Application of chlorine-containing cleaning agents
  • Contamination of the air
  • Mold and mildew in transport bundles or the private stock location     

26. Are there still other causes for the origin of cork taint in the wine and how can these be kept separated from each other? 

Off aromas in the wine can be caused by among other things chlorine-containing cleaning agents or a contamination of the wine cellar. Moreover, there is a contaminant, which is very similar to the "real" cork taint, which is the Tribromanisole (TBA) molecule, with which, as everybody knows, many wine cellars are challenged. Nevertheless, TBA has its causes in chlorine-containing wood treatments and penetrates about the cellar air and around the cork and the wine. The "real" cork taint (TCA) can be separated from these other "taints" in the laboratory... analytically, unambiguously and proved.