Cork: Biology, Production and Uses

Helena Pereira, Helena Pereira

• Publisher: Elsevier Science
• Year: 2011
• ISBN:
  9780080476865
• Topic: Tecnología e ingeniería
• Subtopic: Silvicultura

This comprehensive book describes cork as a natural product, as an industrial raw-materials, and as a wine bottle closure. From its formation in the outer bark of the cork oak tree to the properties that are of relevance to its use, cork is presented and explained including its physical and mechanical properties.

The industrial processing of cork from post-harvest procedures to the production of cork agglomerates and composites is described.

Intended as a reference book, this is the ideal compilation of scientific knowledge on state-of-the-art cork production and use.

• Presents comprehensive coverage from cork formation to post-harvest procedures
• Explains the physical properties, mechanical properties and quality of cork
• Addresses topics of interest for those in food science, agriculture and forestry

Part I

Cork biology

Outline

Chapter 1: The formation and growth of cork

Chapter 2: The structure of cork

Chapter 3: The chemical composition of cork

Chapter 1

The formation and growth of cork

Publisher Summary

The cork that is known from wine bottles is extracted from the bark of the cork oak tree. In plant anatomy, cork is a tissue named phellem and is part of the periderm in the bark system that surrounds the stem, branches, and roots of dicotyledonous plants with secondary growth. Cork is a protective tissue that separates the living cells of the plant from the outside environment. The formation of cork in the periderm is the result of the activity of a secondary meristem, the cork cambium, or phellogen. A general introduction to tree barks and to the formation of cork tissues in barks is presented in the beginning of this chapter. The formation of the first periderm in the cork oak is the illustrating by explaining the formation of the phellogen, the initiation of its meristematic activity, and the differentiation and maturing of cork cells as well as the differentiation and activity of the traumatic phellogens that originate the successive traumatic periderms that are formed during the tree exploitation. The formation and development of the lenticular channels in the cork tissue are also discussed. Finally, an analysis of the successive annual growth of cork is made in conjunction with a discussion on the sustained cork production.

1.1. Bark and periderm in trees

1.2. Periderm and cork formation in the cork oak

1.3. The formation of lenticular channels

1.4. The growth of cork

1.5. Conclusions

References

The cork that we know from wine bottles is extracted from the bark of the cork oak tree (Quercus suber L.). In plant anatomy, cork is a tissue named phellem and is part of the periderm in the bark system that surrounds the stem, branches and roots of dicotyledonous plants with secondary growth. Cork is a protective tissue that separates the living cells of the plant from the outside environment.

The formation of cork in the periderm is the result of the activity of a secondary meristem, the cork cambium or phellogen. The cellular division of the phellogen is linked to the physiological cycle of the tree and to the factors that influence it, namely the environmental conditions.

In relation to other trees, the periderm of the cork oak has special characteristics of development, regularity, growth intensity and longevity that have singularised this species. Upon the death of the phellogen, even if in large areas of the stem, as it occurs during the man-made extraction of cork, there is a rapid formation of a traumatic phellogen that resumes its functions as a producer of the protective cork layer. This response of the tree is repeated whenever necessary. These features open up the possibility of using the cork oak tree as a sustainable producer of cork throughout its lifetime and they are the basis for the use of cork as an industrial raw material.

A general introduction to tree barks and to the formation of cork tissues in barks is made in the beginning of this chapter following the general description of plant anatomy (Esau, 1977; Fahn, 1990). The formation of the first periderm in the cork oak is detailed by showing the formation of the phellogen, the initiation of its meristematic activity, the differentiation and maturing of cork cells as well as the differentiation and activity of the traumatic phellogens that originate the successive traumatic periderms that are formed during the tree exploitation. The formation and development of the lenticular channels in the cork tissue are also presented. The analysis of the successive annual growth of cork is made in conjunction with a discussion on the sustained cork production.

1.1 Bark and periderm in trees

When looking at a cross-section of a tree stem, the distinction between two main parts can be made: the inner part is the wood (anatomically named xylem), located to the inside of the cambium, and the outer part to the outside of the cambium constitutes what is named bark (Fig. 1.1).

Figure 1.1 Schematic drawing of a cross-section of a tree stem showing the wood, the phloem and the periderm and the location of the lateral meristems (cambium and phellogen).

The bark is not homogeneous and is constituted by two types of tissues, from inside to outside: the phloem, produced by the cambium, and the periderm that is the result of the activity of another meristem, the cork cambium or phellogen. The phloem is the principal food-conducting tissue in the vascular plants, and it may be divided into an inner functional phloem and an outer non-functional phloem (also called non-collapsed and collapsed phloem, respectively). The periderm is a system with a three-part layered structure: (a) the phellogen, or cork cambium, is the meristematic tissue whose dividing activity forms the periderm; (b) the phellem, or cork, is formed by the phellogen to the outside; and (c) the phelloderm is divided by the phellogen to the interior.

In most tree stems, one periderm is only functional during a limited period, and it is substituted by a new functioning periderm ...