Tannic acid

What is tannic acid?

Tannic acid, also known as tannin or tannin, is a fascinating class of polyphenolic compounds found in many plant species, especially trees. This substance is not only an essential component of plant defence mechanisms, but also a key element that contributes significantly to the longevity and robustness of wood.

Smoked oak wood | Photo © by Hugo Kämpf

The chemical nature and its profound effects

Tannic acid impresses with its versatile properties, of which the astringent effect is particularly noteworthy. This ability to bind proteins and contract tissue gives tannic acid its characteristic effect, which is expressed in the furry feeling in the mouth after eating unripe fruit. However, this property is more than just a sensory experience: it plays a crucial role in protecting the wood from biological threats. Thanks to its antibacterial and antifungal effects, tannic acid protects the wood from decomposition and fungal attack, thus extending its lifespan.

Another remarkable phenomenon is the reaction of tannic acid with iron.

Discolouration due to pieces of metal inside an oak tree | Foto © by Hugo Kämpf

This chemical interaction leads to dark, often bluish-black discolouration in the wood, which can occur when tools or fastening materials containing iron come into contact with wood containing tannic acid. This reaction gives the wood a characteristic patina that makes it unique and valued. In addition, the tannic acid affects the natural colouring of the wood, bringing out warm, brownish tones and giving the wood a distinctive depth.

Occurrence and far-reaching significance

Tannic acid is found in different types of wood in varying concentrations. Oak wood, known for its robustness and durability, contains particularly high amounts of tannic acid, followed by walnut, chestnut and ash. Softwoods also contain tannic acid, but in much smaller quantities.

The role of tannic acid is of great importance in wood processing. It guarantees the resistance and durability of wood products, but at the same time can lead to undesirable discolouration, especially when it comes into contact with iron. This dual effect of tannic acid - protection and patina - makes it a complex and fascinating component of wood.

Traditionally, tannic acid was used in leather production to preserve animal hides and protect them from rotting. Binding to the proteins in the hide makes it more resistant and durable. Tannic acid also plays a decisive role in the art of winemaking: it not only influences the colour and structure of the wine, but also gives it a characteristic astringency that contributes to the complexity of the flavour profile.

Tannic acid is also used in medicine due to its astringent and antimicrobial properties. It is used in the treatment of diarrhoea, inflammation and minor skin injuries, although medical advice is always recommended.

Practical tips for handling wood containing tannic acid

When working with wood that is rich in tannic acid, tools containing iron should be avoided to prevent unwanted discolouration. But beware, tannic acid can trigger allergic reactions in some people. A doctor or pharmacist should therefore always be consulted for medical applications.

Tannic acid explained simply

Tannic acid acts like invisible armour for oak wood. It protects the wood from decay and fungal attack and gives it its characteristic brown colour. However, if the wood comes into contact with iron, dark stains can appear.