From flax to linen. Experiments with flax - Ribe VikingeCenter

4. FROM PLANT TO YARN
With one exception the flax grown in 2010 was not used in the further experiments. Instead we
used four batches of flax grown at the Centre in 2008 (batch 1) and in 2009 (batch 2-4). Most of
the experiments described in the following actually took place while the flax described in chapter
3 was still growing in the field. It was therefore very practical to have the crop from previous
years available, as is possible in an established institution such as Ribe Viking Centre.
Retting
Retting is a fermenting process where the flax is allowed to rot slightly. The process dissolves the
glue binding the fibres together. This glue consists of lignin and pectin and keeps the plant tissues
together.
As already mentioned in chapter 1, there are two main ways to do retting; water retting and dew
retting. When water retting, the flax is laid out in stagnant or slow running water, held down by
stones or other heavy objects, ensuring that the flax is completely under water. A number of
bacteria work to dissolve the plant glue. These bacteria develop spontaneously from germs in the
soil so it is not surprising that many different micro organisms have been isolated during the
retting process (Tanner 1922; McClung 1956; Bjørn 1974; Sing et al. 2008). The bacteria active
in this process are all anaerobe (Clostridia). Some of these are important pathogens, such as
Clostridium Botulinum and C. perfrigens, both of which has been proven active in the retting
process and can cause dangerous diseases. This could explain the ban against retting in watering
holes, which is found in early modern bylaws, such as those from Sønder Jernløse in 1598 and
Rønninge in 1601 (Bjerge & Søegaard 1906).
The variety of bacteria found active in the retting process seems to indicate that they vary
according to soil type and climate, and that every region will have its own set of retting bacteria.
It has been found that it is the combination of different bacteria that make retting possible.
Experiments with isolated bacteria have been performed and it was found that no bacterium on its
own would initiate the retting process (Jacobsen 1958). The bacteria decompose the plant pectin,
leaving the fibres, but if the retting process is continued for too long cellulose fermenting bacteria
and fungi develop and the fibres are also destroyed (Sing et al. 2008). It is important that the
retting is not stopped too soon or too late. If the flax is allowed to ret for too long the fibres will
have rotted and be useless. If it is retted too little it will not be possible to separate the fibres from
the shives. However, the retting process can be stopped and started again by drying out the straws
to stop the process and laying them out to start it up again. This means that it is better to allow the
retting process to be cut short rather than letting it go on for too long as the retting can always be
started again if it should turn out that the flax is not yet ready for breaking. Once the retting
process is done the straws must be dried out completely before they are processed further.
Because of the toxins and microorganisms that develop, it is best to change the water regularly
before it is too contaminated. Retting is faster in very contaminated water but it can easily get out
of control and is easier to handle when changing the water. A bucketful of old retting water can be
added to speed up the process slightly when retting a new batch. The warmer the water, the faster
the retting process will be, but care is needed as the retting can be very quick. After about 1 or 2
weeks when the flax starts to stink it is taken out of the water and rinsed in cold water to stop the
process, and then dried out completely (Møller Hansen, K. & Høier, H. 2000).
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