Smoking
When split herring are hung in a stream of smoke, two things happen: chemical constituents of woodsmoke are deposited which give the kipper its characteristic flavour and also act as a very mild preservative, and some of the moisture in the fish is lost by drying, thus making the texture firmer. Hardwood chips and sawdust are burned to produce the smoke.
Brined, dyed, fat herring take four hours in a mechanical kiln with all fires lighted to yield well cured kippers, and during this time should lose on average about 14 per cent of their brined, drained weight. The temperature of the kiln should not rise above 30°C. A weight loss of about 10 per cent during smoking is necessary to obtain the typical texture of a kipper when using lean herring, whereas a weight loss of up to 20 per cent can be tolerated when kippering very fatty herring without the product tasting too dry. Thus, although it is reasonably straightforward to make kippers of uniformly good quality in a mechanical kiln, the operator must have some knowledge of the raw material in order to obtain the right amount of drying and at the same time produce the desired smoky flavour. In large installations it is worth while making regular checks on weight loss by first weighing the empty trolleys complete with tenters or trays, weighing the same trolleys when loaded with fish after dripping and, finally, weighing again after smoking. The trolleys can also be weighed at the half-time turnround as a process check during smoking. Weight loss can be checked on a smaller scale by weighing individual tenters or trays.
Full details of the design and operation of mechanical smoking kilns are given in the publication ‘Fish Smoking: A Torry Kiln Operator’s Handbook’ by G. H. O. Burgess and A. McK. Bannerman, published by Her Majesty’s Stationery Office, 1963.
The smoking of kippers in a traditional chimney kiln is a slower and less easily controlled process; it is impossible to give precise smoking times because so much depends on outside weather conditions and on the ability of the smoker to control his fires, re-arrange the tenters during smoking and strip the kiln on completion. Even the most experienced smoker has difficulty in turning out uniformly smoked and dried kippers, both within a batch and from one kiln loading to another. Typical smoking times range from 6-12 hours.
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