The bog environment
Raised bogs consist of a dense network of small sphagnum plants. These sphagnum plants produce acid, which over time, create a very acidic environment. This, in combination with the lack of oxygen means that bogs become a virtually antibacterial environment. However, there are micro-organisms that do tolerate and even thrive in such environments, so there must be another reason for the excellent preservation of bog bodies and other finds.
Sphagnum Moss
Once again, it is the Sphagnum plant that does it. If Sphagnum dies, it releases a natural sugar compound called sphagnan. This neutralises any nutrients in the bog, thus starving any bacteria present and halting the process of natural decay for which these microorganisms are responsible. Sphagnan preserves bodies by tanning the soft tissues, turning skin into leather. In this process the skin is coloured brown and hair becomes red, which is why all bog bodies with hair are red-heads, regardless of their original hair colour. Sphagnan also makes keratin in horn, nails and hair more resistant to decay, but it decalcifies bones, making them soft and flexible.
A prehistoric refrigerator?
Although the chemical processes responsible eluded past people, the preservative qualities of bogs were well-known. It seems that prehistoric people may have used bogs occasionally to store food. Many wooden barrels of butter have been found in bogs in England and Scotland, as well as a suckling pig and pieces of cheese. Some of this food may have been deposited in the bog as an offering to the gods in a very similar way as bog pots with food in Denmark, but bogs may also have been used as a sort of refrigerator.
People's awareness of the preservative qualities of bogs is also reflected in a find from Cladh Hallan in Scotland suggests. Here several people had clearly been buried long after their death. It seems they had been kept in a bog which preserved their soft tissues until they were buried. In the historic period, the Vikings preferred to carry bog water on long journeys as it stayed fresh much longer. Irish soldiers in World War I, used antiseptic and healing sphagnum moss to treat their wounds when they lacked sterile bandages, which saved many lives.