Fish products and Byproducts Technology

Unit 4 - Fish preservation by smoking

4.4. Materials used to produce the smoke
Smoke is prepared by "smouldering fibre" i.e. burning without flame. The source of producing smoke is the wood. All types of wood are not suitable for smoking purpose. Depending on types of wood odour and taste differs. For smoking, hard wood is suitable and we should not use soft wood. Types of wood used for smoking are mentioned below.
• Coconut shell and husk
• Sag wood dust
• Sag wood ships (leaves)
• Mango wood
• Paddy husk etc.
The species source of the sawdust affects end product flavour. Hard woods, such as oak, hickory, cherry, apple and beech, burn to give a smoke with more phenols, which both preserve and give a characteristic, ‘medicated’ flavour to the product.
What are all the chemical constituents of wood?
Freshly cut wood contains 40-60% moisture which is not suitable for smoking. A good wood containing <25% moisture is preferred for smoking. If the moisture is more than 25% then it is considered as damp wood. When wood is burnt it gives compound mixture of chemicals in addition to main gas like CO₂ and traces of H₂O and CO.
Wood consists of two parts
Combustible
Non combustible
Combustible substances
The main combustible substances are divided into three parts.
• Polyoses
• Lignins
• Resins (to some extent),
Polyoses
• Polyoses contain cellulose and hemicelluloses.
• The main component of hard wood
• In hard wood, polyoses comprise 2/3 rd of the wood.
• When wood is burnt polyose part gives out aliphatic chemicals and when temperature reaches 280^oC, the released chemicals are alcohol, aldehyde, ketone and acids.
Lignins
• The main components of hard wood
• In hard wood, lignin comprise 1/3 rd of the wood.
• Lignin part is resistant to heat and when temperature reaches 350^oC, they will burn and give out phenolic compounds.
Resins
• More common in soft wood eg. turpentine.