Handbook of Meat Processing

Smoking 241

chips of low mesh size is kept below 400 ° C

to prevent self - ignition. The composition of

the smoke can be controlled by modifying

the content of oxygen in the air mixture. Self -

ignition of the fl uidized sawdust bed may be

prevented even at a temperature as high as

750 ° C if the concentration of oxygen in the

gas mixture is reduced to 6% (Balejko and

Miler 1988 ). The quality of the smoke pro-

duced in a fl uidized bed at such a high tem-

perature is equal to that from a smoldering - type

generator.

Smokehouses

Introduction

Meats and meat products can be successfully

smoked in very simple devices (e. g., in a

barrel inverted over a pile of smoldering

sawdust, fi tted with supports for spits, rods,

or wire mesh, and outlets for the spent

smoke). Here, as well as in smoking ovens,

but also in kilns or tunnels supplied with

smoke from generators, the quality of the

products is affected by the duration of the

process, the properties of the smoke, and

the conditions of heat and mass transfer. The

same factors are also important in smoke-

houses equipped with atomizers of liquid

smoke preparations. Additionally, in smoking

and steaming chambers, the parameters of

the heating steam have to be considered, as

do the effects of the high - voltage electro-

static fi eld in electrostatic smoking units.

Smoking Ovens

Smoking ovens, generally built as a cross

section of a rectangle, about 1 m wide, 1.2 m

deep, and 2 m high, have stony fl oors and

fi reproof brick walls. On the side walls, there

are two or three pairs of supporting rails at

appropriate distances to allow for sliding the

frames on which the meat products hang

from spits or rods. On the front of the oven

there are three doors: two small ones at the

rations in the rotor. The temperature in the
friction zone may be controlled by adjusting
the pressure applied to the log and the speed
of rotation of the rotor. It is usually 300 –
350 ° C. The smoke is blown into the smoke
duct by a fan that may be fi xed on the shaft
of the rotor. Because of comparatively limited
access of air to the friction zone and low
temperature, the smoke contains fewer prod-
ucts of thermal degradation and oxidation of
lignin than that from the earlier described
generators. The assets of the friction - type
machine are low consumption of wood
and the fact that the smoke production can
be started and stopped instantaneously.
However, because it makes a lot of noise
during operation and needs electrical power
for driving the rotor, it is not very often used
in the industry.

Other Types of Generators

Thermal degradation of wood can also be
accomplished by overheated steam; this takes
place in the steam smoke generators covered
by numerous patents (Fessman 1971 ). The
sawdust is fed by a worm feeder into a reactor
formed by a tilted pipe with perforated walls.
Overheated steam at temperatures of usually
about 200 ° C is blown through the perfora-
tions into the sawdust - fi lled reactor. At this
considerably lower temperature, lignin does
not undergo thermal degradation, and the
smoke is rich in carboxylic acids and car-
bonyl compounds but relatively poor in
phenols and polycyclic aromatic compounds.
In some of these generators, additional
sections of the reactor serve to oxidize the
volatile decomposition products by oxygen -
enriched air.
Wood smoke can also be produced by
blowing a stream of hot air or air/inert gas
mixture countercurrently across a bed of
sawdust that is being fed at a controllable rate
into a fl uidization chamber that has the form
of a truncated cone (Nicol 1962 ). The tem-
perature of the fl uidized bed of sawdust or