at this step to digest the spoiled parts of the hides/skins including those in poor
condition and recover valuable products from the hydrolysate.
7.1.2 Curing and Storage
Curing process is performed to prevent degradation and restrains microbial attack on
hides/skins before processing. For fresh hide processing immediately after skinning,
this step can be omitted. Curing for long-term storage of up to 6 months includes
drying, salting and brining [5]. Long-term preservation methods are used when the
tannery anticipates shortage of the products in the market or when trading the hides
and skins especially for intercontinental trading. Short-term curing involves preserving for 1–6 days using methods such as cooling, refrigeration and addition of
biocides. These methods are used when raw materials are directly received from
local sources. The raw materials are generally stored as they are received by the
tannery on pallets in ventilated or air conditioned and/or cooled areas, depending on
the method of curing chosen. The stored hides/skins are then taken to the beam house
for processing.
7.2 Preparation for Skins and Hides for Tanning
The process in the beam house of the tannery involves removal of the skins or hides
from storage and their preparation for tanning and is often carried out in processing
mixer vessels or rotating drums.
7.2.1 Enzymatic Soaking
Soaking allows the hides/skins to rehydrate and helps in opening up the contracted fibre
structure [15]. Soaking is necessary for solubilisation and removal of interfibrillary
material and cleaning the hides and skins from dirt (salt, soil particles, dung, blood
remains and soluble proteins on the surface of the skin). Soaking is mostly executed in
two steps. First there is a dirt soak which removes salt and dirt. The second soak is also
known as main soak which is longer and may last between 8 and 72 h. Due to the long
soaking period in the main soak, in traditional leather processing method, putrefying
bacteria thrive, and biocides are added to curtail their activity and growth [38].
Application of alkaline protease in the dirt soak and main soak reduces processing
time and initiates the fibre opening of the hide and skin tissue. Enzymatic soaking is
successfully carried out under alkaline conditions using proteolytic enzymes that are
optimally active in alkaline conditions. The advantages of enzymatic soaking include:
• Loosening of the scud
• Partial dehairing during soaking process
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W. C. Wanyonyi and F. J. Mulaa
condition and recover valuable products from the hydrolysate.
7.1.2 Curing and Storage
Curing process is performed to prevent degradation and restrains microbial attack on
hides/skins before processing. For fresh hide processing immediately after skinning,
this step can be omitted. Curing for long-term storage of up to 6 months includes
drying, salting and brining [5]. Long-term preservation methods are used when the
tannery anticipates shortage of the products in the market or when trading the hides
and skins especially for intercontinental trading. Short-term curing involves preserving for 1–6 days using methods such as cooling, refrigeration and addition of
biocides. These methods are used when raw materials are directly received from
local sources. The raw materials are generally stored as they are received by the
tannery on pallets in ventilated or air conditioned and/or cooled areas, depending on
the method of curing chosen. The stored hides/skins are then taken to the beam house
for processing.
7.2 Preparation for Skins and Hides for Tanning
The process in the beam house of the tannery involves removal of the skins or hides
from storage and their preparation for tanning and is often carried out in processing
mixer vessels or rotating drums.
7.2.1 Enzymatic Soaking
Soaking allows the hides/skins to rehydrate and helps in opening up the contracted fibre
structure [15]. Soaking is necessary for solubilisation and removal of interfibrillary
material and cleaning the hides and skins from dirt (salt, soil particles, dung, blood
remains and soluble proteins on the surface of the skin). Soaking is mostly executed in
two steps. First there is a dirt soak which removes salt and dirt. The second soak is also
known as main soak which is longer and may last between 8 and 72 h. Due to the long
soaking period in the main soak, in traditional leather processing method, putrefying
bacteria thrive, and biocides are added to curtail their activity and growth [38].
Application of alkaline protease in the dirt soak and main soak reduces processing
time and initiates the fibre opening of the hide and skin tissue. Enzymatic soaking is
successfully carried out under alkaline conditions using proteolytic enzymes that are
optimally active in alkaline conditions. The advantages of enzymatic soaking include:
• Loosening of the scud
• Partial dehairing during soaking process
206
W. C. Wanyonyi and F. J. Mulaa