64
Exploitation of Straw for Food
real. Costly equipment was needed and a level of
intelligence required for its application which pre-
cluded its use by other than at least semi-skilled
labour. At a specialized central depot, however,
where a plant was installed which was capable of
dealing with large quantities, a material of high
feeding value was produced at a cost which was not
unduly great, that is when the treated straw or
' straw pulp' was used in its wet state. But
therein lay the difficulty, because the water content
of the pulp is very high, the transport of water is
expensive, the process of drying is costly, and the
semi-dried material is a favourable medium for the
growth of moulds. The straw could then be used
only in an area in proximity to the plant, in order
to avoid the difficulties of transport and storage.
The usefulness of this method of treating straw
under factory conditions was thus greatly restrict-
ed, but, all the same, during the last European
War many large-scale plants were installed in
Germany.
As a result of the intensive study of the subject
which was undertaken at that time, it was found
that there was no necessity to carry the digestion
of straw to the extent done in the paper industry.
There the complete removal of the indigestible
enveloping substances is aimed at and is achieved
only at the expense of large amounts of organic
material or potential food. Fairly strong concen-
trations of alkali and pressure steaming are the
means adopted to that end. To greatly increase
the food value of straw it is sufficient to disrupt the
incrusting material and to spring the ligno-cellulose
bond ; in the process, the silica may be separated
and dissolved and the methoxy and acetyl group
split off the lignin molecule. It was discovered
that this could be attained quite well when weak
solutions of caustic were used, and it was also de-
monstrated that steaming at high pressure was not
necessarily beneficial. Thus the expensive high-
pressure process was discarded in favour of the use
of weak alkali solution at low pressure. The re-
sulting product is of an acid or neutral reaction
because sufficient acetic acid is formed from the
liberated acetyl group to neutralize the compara-
tively small amount of alkali. The process was in
the meantime carried a step farther when cooking
in open vats was advocated. A stronger solution
of caustic soda was, however, employed and the
treated straw had to be freed from alkali by wash-
ing before it could be fed. In washing there was
an unavoidable loss of organic material which went
far to offset the benefits which the simplified process
otherwise afforded.
At Leeds in 1917 Godden, making use of the
lessons already learnt on the Continent, devised a
simple process which could be used on the farm.
He recommended that chopped straw should be
soaked overnight in a 1.5 per cent solution of
caustic soda, and on removal from the solution it
should be well drained and put into a steamer,
such as forms a fairly common piece of equipment
on a modern farm. The particular one he devised
consisted of a vertical iron boiler with a loose cover
and fitted with a pipe which delivered steam near
the base. Steam was blown through the soaked
straw in this tank until the whole mass was at
boiling-point, steaming being continued for an
hour. The treated straw was allowed to drain and
cool before being fed. It required no washing,
because the soda had been sufficiently neutralized
during the steaming. He showed that there was,
on the whole, about 50 per cent gain in feeding
value.
While Godden was doing this work in England,
Beckmann introduced his method which differed
radically from all the previous ones in that it did
not involve the use of heat. He proved, too, that
even under such conditions a weak solution of
alkali was as effective for the purpose in hand as a
strong solution and that the time required for its
action was comparatively short. In spite of the
fact that by his process final washing of the straw
is required, the method is so simple and so econo-
mical that it quickly superseded all the others.
The hydrolysis of the straw is carried out with
eight times its weight of 1.5 per cent solution of
caustic soda for three hours, the fluid is then run
off and the residue washed with water until it is
neutral to litmus. The results of feeding trials,
digestibility and metabolism experiments show
that, in general, for ruminants, the nature of the
improvement in food value is in the region of 100
per cent.
Hydrolysis of straw can be accomplished with
material other than caustic soda—such, for inst-
ance, as calcium hydroxide and sodium carbonate,
or by acids such as hydrochloric, sulphuric or
nitric. Lime and sodium carbonate are consider-
ably less effective than sodium hydroxide unless
heat is used, when their action compares very
favourably with that of caustic soda. The action
of the acids is not sufficient in any case to make
their use worth while.
Today Beckmann's process is being experi-
mentally operated on many farms in Britain, and
feeding trials on ruminants are also being conduct-
ed under the auspices of the Agricultural Research
Council. The result of these trials and in parti-
cular the reports on the suitability of the process
to English farm conditions may be of some import-
ance. The plant most generally adopted is one of
two devised by Imperial Chemical Industries, Ltd.
One of these consists of twin concrete basins into
either of which is placed the chopped straw, both
while it is being subjected to the action of the
caustic soda and while it is being washed. After
the straw has soaked sufficiently in a 1.25 per cent