232 Chapter 12
coalescence of some particles. Due to the
action of the gravitation and centrifugal
forces, as well as the temperature gradient,
some components are deposited on the
smoked goods, in the smoke ducts, and on
the walls of the smokehouse. This leads to
changes in their concentration in the smoke.
The surface electrical charge of the particles
also contributes to the physicochemical state
of the aerosol. The dispersed components
absorb and disperse light; thus their concen-
tration affects the optical density of the
smoke. The optical density is proportional to
the number of particles in a unit volume of
the smoke. In constant conditions, when the
dimensions of the particles do not change, the
optical density is correlated to the mass con-
centration of the dispersed components in the
smoke. Thus photo optical measurements can
be used for the determination of smoke
density, which refl ects the contents of all
components.Chemical Composition of Smoke
Introduction
The chemical composition of smoke and
smoke condensates produced from various
kinds of wood was comprehensively reviewed
over two decades ago (T ó th and Potthast
1984 ). In numerous later publications, the
effect of the conditions of smoke production
prevailing in different generators has also
been investigated.
Wood smoke contains air, water vapor,
CO 2 , CO, and at least several hundred organic
compounds in different concentrations.
About 400 of them have been unequivocally
identifi ed by chromatographic and spectral
analytical methods. The composition of the
smoke depends on the kind of wood used for
smouldering (i.e., mainly on its dryness and
the contents of hemicelluloses, cellulose,
lignin, and resins), as well as on the tempera-
ture and access of air to the zone of oxidation
of the volatile products. The content of wateruse, along with procedures for their
application.
Curing Smoke
Generation and Properties of
Wood Smoke
Curing smoke develops as a result of the
partial burning of wood with a limited oxygen
supply. Generally, hardwood is used, mainly
oak and beech. However, for imparting spe-
cifi c color or fl avor to some products, wood
from other trees that are rich in resins, includ-
ing coniferous, as well as heather, may be
used. In some areas, other carbohydrate -
rich material (e.g., bagasse [sugarcane], beet
refuse from sugar making, or coconut husks)
is used.
The smoke consists of gaseous products
of thermal degradation and subsequent partial
oxidation of the wooden material and of the
dispersed soot and compounds present in
fl uid or particle form. The temperature of
thermal degradation in the wood constitu-
ents — hemicelluloses, cellulose, and lignin —
ranges from 180 ° to 300 ° C, 260 ° to 350 ° C,
and 300 ° to 500 ° C, respectively. The tem-
perature in the glowing zone may even reach
up to 900 ° C.
The numerous components of the smoke
differ in chemical and physical properties.
The gases and low - boiling compounds con-
stitute the gaseous phase, while the higher
boiling ones are dispersed in the form of fl uid
droplets or solid particles. The mass of the
dispersed phase makes up about 90% of the
total mass of the smoke. The proportion of
different smoke constituents in both phases
depends not only on their chemical composi-
tion, but also on the conditions of smoke
generation and the temperature and turbu-
lence in the duct leading from the generator
to the smokehouse. Cooling increases the
weight proportion of the higher boiling com-
pounds, while heating raises the concentra-
tion of vapors. Brownian motion leads to