Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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uniform throughout the product. This is true if

products are dipped or injected with the liquid

smoke, but not if liquid smoke is only sprayed on to

the product surface.

0050 The composition of commercial liquid smoke can

vary widely, depending on the method of manufac-

ture. Natural smoke extracts, synthetic smoke flavors,

and substances unconnected with smoke, such as yeast

derivatives but with a smoky flavor or smell, are used.

0051 The use of liquid smoke also reduces the undesirable

PAH levels in smoked foods. The European Scientific

Committee for Food, in its Directorate-General Indus-

try Guidelines (1995) established that smoke flavor-

ings (liquid smoke) added to a food product must

assure a level lower than 0.03 mg of benzopyrene per

kilogram and less than 0.06 mg of benzoanthracene,

another PAH compound, per kilogram.

0052 In the meat industry, liquid smoke is commonly

used in place of traditional smoke. However, smoke-

flavored fish represents a small percentage of the total

smoked fish industry output.

Smoked Food Products Quality and Safety

Microbiological Safety

0053 The intrinsic microbiological stability of smoked

foods is dependent on the ingredients, additives, and

processes. In one extreme are traditional products

usually heavily cured and smoked, which can be

stable for many months at ambient temperatures; at

the other extreme, there are lightly cured and smoked

products, whose stability is dependent on extrinsic

factors such as refrigeration, vacuum, or gas packing.

0054 The length of the smoking process for cold-smoked

products is much longer than for hot-smoked prod-

ucts, but a pasteurization temperature is not achieved

in any stage of the process. Thus, the temperatures

and times used in processing cold-smoked products

are very favorable for the proliferation of food spoil-

age and food poisoning types of microorganisms.

0055 Most of the commercialized smoked products in

Western countries are sold vacuum-packed and stored

at refrigeration temperatures, and so spoilage and

food poisoning flora of the finished products are

mainly anaerobic or microaerophilic, and psychro-

trophic or psychrophilic.

0056 Cold-smoking, or any smoking process where tem-

peratures in the interior of the foodstuff do not reach



C for a significant period of time, will have a

different residual postsmoking microflora than those

hot-smoked products where a high internal tempera-

ture is reached.

0057 The temperature achieved during hot-smoking kills

vegetative microorganisms but not all spores, so the

most probable spoilage agents will be spore formers or

postsmoking contaminants. Refrigeration of hot-

smoked fish greatly reduces the number of organisms

able to grow and lengthens the shelf-life of the product.

0058Cold-smoked products will contain a microbial

flora representative of that of the raw material. The

salt in the water phase must be high enough to inhibit

the growth of Clostridium botulinum (3%), but

this will not stop the growth of spoilage bacteria.

Immediately after vacuum packing, bacterial counts

in cold-smoked salmon, commonly range between

and 10

1

, and at the end of the shelf-life (6

weeks), the product typically contains a microflora

dominated by lactic acid bacteria at levels of 10

–

1

. The use of drying and/or salt to lower the

water activity and smoke to add chemical preserva-

tives limits the types of microorganisms capable of

growth, and the production process affects the micro-

bial flora present on the product; therefore, both of

these affect the spoilage patterns. Spoilage needs to be

defined carefully for each product.

0059Listeria monocytogenes has been found consist-

ently in smoked fish products. Nitrites, usually

added to smoked meat products, are known to inhibit

growth of C. botulinum and also can inhibit L. mono-

cytogenes growth. (See Listeria: Properties and

Occurrence.) Nitrites also can be added to cheese to

prevent very late fermentation and gas production by

Clostridium tyrobutyricum or C. butyricum.

0060For C. botulinum, levels of salt higher than 3% in

the water phase together with refrigerated storage can

prevent growth and toxin production in cold-smoked

fish products, even when nitrites are not added. How-

ever, with respect to L. monocytogenes, which is able

to grow at salt levels up to 10% and temperatures as

low as 1



C, when nitrites are not allowed in fish

products (EU) there is no step in the cold-smoked

process that is able to prevent its growth.

0061The International Commission for Microbiological

Specifications for Foods recognized that numbers of

L. monocytogenes not exceeding 100 g

1

at the time

of consumption are of low risk to the consumer.

Therefore, for ready-to-eat, not heat-treated, foods,

where the presence of L. monocytogenes cannot

be fully avoided, the critical points are to limit the

occurrence of L. monocytogenes in foods but, more

importantly to control its growth and survival in

order to keep levels below the 100 g

1

at the point

of consumption. This policy is followed by some

European countries but is considered a hazard

by USA, which maintains a zero-tolerance policy

regarding Listeria incidence in ready-to-eat foods. If

a zero-tolerance policy were to be established in EU

countries, where nitrites or other antimicrobial addi-

tives are not allowed to be added to fish products, this

SMOKED FOODS/Production 5307

would lead to the cessation of sales of cold-smoked

fish products where the presence of L. monocyto-

genes cannot be fully avoided. For cold-smoked fish

products, using reliable raw material and good manu-

facturing practices (GMP), keeping storage tempera-

tures under 4



C, and reducing the shelf-life to 3

weeks, has been reported to be sufficient to maintain

L. monocytogenes numbers below 100 g

1

0062 Nisin, the only approved bacteriocin allowed to be

added to foodstuffs, and commonly used in milk

products to prevent C. tyrobutyricum, is also capable

of preventing C. botulinum and L. monocytogenes

growth in smoked products. Recent studies on the

application of different bacteriocins from Carnobac-

terium spp. to cold-smoked fish products to inhibit

L. monocytogenes growth have yielded encouraging

results on inhibiting the growth of this pathogen.

0063 Cold- and hot-smoked foods, like every food

commodity, can potentially cause safety problems. To

improve the safety of commercially smoked products,

producers should use reliable raw materials, improve

smoking technologies (temperature and humidity con-

trol), assure plant equipment and personnel hygiene,

and implement GMP and hazard analysis and critical

control points. (See Hazard Analysis Critical Control

Point.)

Chemical Safety

0064 Preventing the occurrence of carcinogens during

smoking has been an issue for several years. There

are two groups of chemicals of concern in smoke:

PAH and N-nitrosamines (NNAs), both of which

are considered potential carcinogens. The compound

benzopyrene, the most concerning PAH, is regarded

as an indicator of carcinogenicity.

0065 As mentioned before, there are several means for

reducing PAH formation. The use of a separate smoke

generator, maintaining the temperatures of pyrolysis

between 200 and 425



C, electrostatic filtration of the

smoke, smoke generated by superheated steam or the

use of liquid smoke are some of the ways of reducing

the PAH levels in smoked foods. Reports on the

quantification of PAH in smoked fish, meat, and

cheese have suggested that as, in this last product,

the rinds are removed before consumption, the PAH

intake would be much lower. However, in some trad-

itional cheeses, where manufacture includes heating

the milk on an open wood fire, or in commercial hot-

smoked cheeses, the levels of PAH are considerably

higher compared with liquid smoked samples.

0066 The NNAs in smoked food are primarily formed

by the reaction of nitrogen oxides (generated from

nitrites) of the wood smoke with, mainly, secondary

amines present in the flesh. (See Nitrosamines.)

0067Nitrates and nitrites used in smoked meats to

impart color and flavor and due to its antimicrobial

ability are an additional risk factor, as they may react

with both secondary and tertiary amines of the prod-

ucts leading to the formation of NNA. The reaction

can occur during processing, reactive substrates are

amino acids, and many of the resulting NNAs have

been identified as carcinogens. Reducing agents, like

ascorbic acid, added together with nitrites to the brine

to improve NO

activity, also can act as efficient

factors inhibiting NNA formation. Considerable

research attention has been paid to determining the

levels of occurrence and formation of these sub-

stances in foods. It is currently considered that nitrite

levels in smoked meat are such to ensure the stability

of the product and to control C. botulinum, while not

presenting a significant risk from NNA.

0068Although nitrites are legally added as preservatives

to smoked products elsewhere, in EU countries, they

are restricted to smoked meats and prohibited in the

fish industry. Therefore, it is expected that smoked

fish products from EU countries are poor sources of

nitrites, and consequently of nitrosamines, compared

with smoked fish produced elsewhere and com-

pared with smoked meat products.

See also: Clostridium: Occurrence of Clostridium

botulinum; Curing; Drying: Theory of Air-drying; Hazard

Analysis Critical Control Point; Listeria: Properties and

Occurrence; Nitrates and Nitrites; Nitrosamines;

Polycyclic Aromatic Hydrocarbons; Water Activity:

Principles and Measurement; Effect on Food Stability

Further Reading

Bosset JO, Buetikofer U, Dafflon O et al. (1998) Occur-

rence of polycyclic aromatic hydrocarbons in cheese

with and without a smoked flavour. Sciences des Ali-

ments 18: 347–359.

Culik J and Kellner V (1995) Toxic compounds arising by

interaction of food constituents with food additives. In:

Davidek J (ed.) Natural Toxic Compounds of Foods,

pp. 229–249. London: CRC Press.

Dafflon O, Scheurer L, Koch H and Bosset JO (2000)

Quantification of nitrated polycyclic aromatic hydro-

carbons in fish, meat products and cheese using high

performance liquid chromatography. Mitteilungen aus

Lebensmitteluntersuchung und Hygiene 91: 158–171.

FAO Fisheries Report No. 604 (1999) FAO Expert

Consultation on the Trade Impact of Listeria in Fish

Products.17–20 May 1999. Amherst, MA.

Final Report of EC FAIR Project CT95–1207 (2000) Spoil-

age and Safety of Cold-smoked Fish.

Foster WW and Simpson TH (1961) Studies of the smoking

process for foods, I. The importance of vapours. Journal

of the Science of Food and Agriculture 12: 363–374.

5308 SMOKED FOODS/Production

Horner WFA (1997) Preservation of fish by curing (drying,

salting and smoking). In: Hall GM (ed.) Fish Processing

Technology, pp. 32–73. London: Chapman & Hall.

Maga J (1988) Smoke generation technology. In: Smoke in

Food Processing, pp. 39–48. Boca Raton, FL: CRC Press.

Storey RM (1986) The technology of traditional smoking.

Proceedings of the Institute of Food Science and Tech-

nology 19: 58–62.

Varnam AH and Sutherland JP (1995) Cured meats. In:

Meat and Meat Products – Technology, Chemistry and

Microbiology. Food Products Series, vol. 3, pp. 167–

223. London: Chapman & Hall.

Vaz-Velho M, Capell C and Gibbs P (1998) Cured, smoked

and dried fish. In: Fish and Seafood. Microbiology

Handbook, vol. 3, pp. 119–155. Leatherhead, UK:

Leatherhead Food Research Association.

Applications of Smoking

J I Ahmad, University of Lincolnshire and Humberside,

Grimsby, UK

Introduction

0001 Smoke used for curing of foods consists of a suspen-

sion of minute particles in a vapor phase making

up an aerosol. It is produced by controlled thermal

combustion of sawdust, wood shavings, coffee husk,

sugar cane pulp, coconut husk, and rice straw, etc.

The composition of smoke varies with the choice of

wood, the temperature of pyrolysis (Table 1), relative

humidity and the moisture content of the wood

(Table 2). The relative concentration of different

components depends on the type of wood used

and the controls adopted during its combustion

(Figure 1 and Table 3).

0002Polycyclic aromatic hydrocarbons (PAH), which

are believed to be carcinogenic, are a well-known

group of constituents of wood smoke (Figure 2).

These compounds are probably formed through

condensation of naphthalene. Their concentration

strongly increases when other organic materials are

added during combustion of wood. (See Polycyclic

Aromatic Hydrocarbons.)

0003Apart from providing desirable color and flavor to

foods, wood smoke contributes to preservation by

acting as an effective antioxidant and a bacteriostatic

and bactericidal agent. Phenolic components of

the smoke contribute to the flavor and aroma of the

product. Smoke also provides a protective film on

the surface of the smoked product, thus providing a

barrier against development of rancidity. Combined

chemical constituents of smoke together with heating

and drying processes are responsible for bactericidal

and bacteriostatic effects. (See Antioxidants: Natural

Antioxidants; Phenolic Compounds.)

Methods of Smoking Foods

0004Basically, three methods are used in the production of

smoke-flavored foods.

The Traditional Method

0005This is the direct incomplete thermal degradation of

wood to produce smoke. It may be carried out either

as hot smoking or as cold smoking, i.e., the criterion

is the maximum temperature to which the product is

exposed. (See Drying: Theory of Air-drying.)

0006Hot smoking Hot smoking involves exposing the

product to at least 80



C and probably up to 100



the intention being to cook the product as well as

smoke and dehydrate it. Duration of smoking depends

on the level of curing required, e.g., light, mild, or

strong and the thickness of the product. Techniques of

smoke generation vary in different parts of the world.

It may be a simple barrel-type smoke oven, inverted

drums with a fire pit at the bottom or located

remotely, or the very latest high-tech equipment as

available in the UK with automatic smoke density,

temperature, and humidity controls.

0007The principles of hot smoking are simple. Smoke is

generated from desired wood (e.g., oak) with a con-

trolled air supply. The product is usually prebrined for

an appropriate period from a few minutes up to several

hours before being placed on the racks where the

smoke is allowed to circulate at a selected rate

and temperature. Modern kilns yield a uniform, clean

product with little waste. There are basically three

tbl0001 Table 1 Influence of the glowing temperature on the phenol,

carbonyl, and acid yields in smoke (in milligrams per 100 g of

sawdust)

Te m p e r a t u r e



C Total phenols Total carbonyls Total acids

380 998 9 996 2 506

600 4 858 14 952 6 370

760 2 632 7 574 2 996

tbl0002 Table 2 Mechanism of smoke formation

(a) Pyrolysis of wood

Up to 170



C Thorough drying

200–260



C Pyrolysis of hemicellulose

260–310



C Pyrolysis of cellulose

310–500



C Pyrolysis of lignin

(b) Secondary reactions of the

pyrolytic products at about 200



Oxidation, polymerization,

condensation, pyrolysis

SMOKED FOODS/Applications of Smoking 5309

types of smoke houses: (1) with natural air circulation,

(2) air-conditioned or forced air, and (3) continuous.

There are many modifications of these three types. Air-

conditioned or forced-ventilation smoke houses have

largely replaced the natural-air type. They allow much

more precise control of smoking through uniform air

movement and good control of temperature. Smoke

houses with endless revolving chains have been de-

veloped specifically for frankfurter production.

0008Cold smoking Cold smoking was introduced as an

alternative to hot smoking in the early part of the last

century. Its general purpose is to impart a desirable

flavor to the product, rather than preservation, which

is achieved by refrigeration at low temperatures. In

the kilns, the smoking temperature is maintained

below 30



C, and the time of smoking may vary

from a few hours to several days, depending on the

product. The shelf-life of the product can vary and

(a)

(b)

(c)

(d) (e)

(OCH

)

OCH

COCH

CO)

CH=CH−CH

CH CH CH

fig0001 Figure 1 Main chemical constituents of ‘hard’ and ‘soft’ woods: 25% hemicellulose (a); 50% cellulose (b) and 25% lignin (c) from

softwood and, with . . . OCH

, from hardwood. Arrows in (c) show splitting points during pyrolysis. Also shown are (d) coniferylalcohol

and (e) sinapinalcohol.

5310 SMOKED FOODS/Applications of Smoking

may depend on whether the product was brined or

not prior to smoking.

Liquid Smoke

0009 Manufacture Low-moisture saw dust is heated to

500–600



C in a combustion reactor, and the resulting

smoke vapor is passed to the primary tar and ash

separation vessel and then on to a packed tower of

ceramic beads. Here, the vapor smoke is condensed.

The condensate is composed of (1) an aqueous phase

made up of a mixture of low-boiling-point fatty acids,

carbonyl compounds, and alcohols (pyroligneous

acid, formalin, and furfurol in particular; formalin

is responsible for immediate sterilization of the

food surface, and the carbonyl compounds are claimed

to be responsible for the formation of a desirable color)

and (2) an immiscible tar or ‘liquid smoke’ (see Table

4). The tarry phase contains cresol, guaiacol, eugenol,

methyl guaiacol, and pyrogallol to mention a few com-

pounds (Table 5). These substances are credited with

the antibacterial and antioxidant effect that smoking is

supposed to have. The liquid smoke is stored in hold-

ing tanks for 2–4 weeks to allow separation of tars and

other colloidal particles containing high levels of PAH,

including benzo[a]pyrene. The remaining filtrate is a

clear liquid that may be used as such, or it may be

further concentrated by fractional distillation and ex-

traction with selective solvents (see ‘Smoke Flavors’).

A schematic method of making PAH-free liquid smoke

on a laboratory scale is shown in Figure 3.

0010The tastes of the tarry and aqueous phases are

different, and opinions differ as to which is to be

preferred. When liquid smoke from different parts

of the world are examined for their relative chemical

constituents, it is confusing to note that some consist

chiefly of acids, others of esters and carbonyl com-

pounds, and some chiefly of phenols (Table 6).

0011There are four basic principles of application of

liquid smoke: atomization, drenching, dipping, and

direct addition. Further technical developments of

these methods can be found under Application of

Smoke Flavors.

0012Application of liquid smoke offers several advan-

tages over the traditional smoking processes in

that it offers consistent quality and a uniform and

tbl0003 Table 3 Smoke compounds from different species of wood

Compound Amount of compound (gramsper100 g of sawdust)

Acacia Beech Oak Whitebeech Spruce Pine

Monocarbonyls 1.70 1.77 2.40 2.50 3.06 3.10

Oxy- and diacarbonyls 1.86 3.60 1.98 4.95 6.30 6.12

Formaldehyde 0.11 0.15 0.14 0.16 0.21 0.20

Acetaldehyde 0.81 0.66 0.63 0.65 1.15 1.00

Acetone 0.64 0.74 0.37 0.69 0.69 0.54

Furfural 0.24 0.18 0.35 0.26 0.21 0.18

NaOH reducing substances 4.56 6.94 4.68 9.75 7.83 7.40

Reducants 0.13 0.16 0.17 0.32 0.21 0.29

Dehydroreductants 1.56 1.32 0.66 2.16 2.10 1.80

Total acids 2.94 4.06 3.56 6.79 3.07 3.17

pH 4.3 4.8 4.0 4.1 3.8 4.7

Esters 8.48 6.69 10.47 10.35 8.08 11.16

Phenols 0.36 0.14 0.16 0.32 0.29 0.29

Benzo[a]pyrene

Benzo[e]pyrene Methylcholanthrene

Pyrene

Fluoranthene

fig0002 Figure 2 Structures of a few important polycyclic aromatic

hydrocarbons found in smoke.

tbl0004Table 4 Composition of marketable smoke condensates from

France, Germany, and the USA

Group Level (%)

Water 11–92

Phenols (determined by GC) 0.2–2.9

Acids 2.8–9.5

Carbonyls 2.6–4.6

SMOKED FOODS/Applications of Smoking 5311

tbl0005 Table 5 Sensorial judgment of a few phenols

Substance Bestjudged

concentration

(mgper100 ml)

Smell Taste

Guaiacol 3.75 Phenolish, smoky, aromatic, sharp, sweet Phenolish, sharp, spicy, smoked-sausage-

aromatic, sweet, dry

Syringol 7.5 Smoky, spicy, aromatic, smoked-sausage-toned,

phenolish, sharp, sweet

Phenolish, smoky, like freshly charred wood,

like whiskey, dry, sharp

4-Methyl-guaiacol 1.9 Sweet, like vanilla, fruity, like cinnamon,

somewhat smoky, pleasantly sharp, phenol

tones

Sweet, like vanilla, caramel-like, aromatic,

pleasant, smoke tones, burning

i-Eugenol 9.8 Sweet-fruity, like vanilla, like rhubarb, phenol

tones

Sweet-fruity, mild smoke tones, dry, sharp

o-Cresol 7.5 Phenolish, sweet-fruity, aromatic, like caramel,

smoked-sausage-tones

Sweet, sharp, unpleasantly smoky, burning

Dimethyl-phenol 0.9 Phenolish, like ink, aromatic, sweet Phenolish, sharp, somewhat charred, sweet,

dry

Laboratory smoke generator

Cooling, condensation, and filtration

of smoke

Smoke condensate (a) aqueous, (b) tar phase

Adjust to pH 6.5−7.0 with about 5% NaHCO

solution

liquid−liquid partition with ethyl acetate

(three or four times)

Organic phase

Filtration through Na

(sicc.) and

concentration to dryness

Nonpurified extract

Steam distillation at 170

liquid−liquid partition between

distillate and ethyl acetate

(Aqueous phase)

Organic phase

Phenol extract

Purified phenol fraction (PAH-free)

Column chromatography through TN

silica gel with 40% ethanol fraction: 0−200 ml

Filtration through Na

(sicc.) and

concentration to dryness

(Tar phase)

(Aqueous solution)

(GC analysis of TMS derivatives)

fig0003 Figure 3 Outline scheme for the preparation of a PAH-free liquid smoke.

5312 SMOKED FOODS/Applications of Smoking

reproducible product. Since the polycyclic aromatic

hydrocarbons, tar and soot are removed in its manu-

facture, it is safer to use. It is economical in terms of

time and ease of application, and there are no fire

hazards.

Smoke Flavor

0013 The toxicological problems associated with conven-

tional smoking of foods have attracted a great deal of

interest in recent years. There is evidence that the

consumption of smoked meats, sausages, and fish

over prolonged periods may be a causal factor in the

development of cancer of the alimentary canal. For

this reason, extensive efforts are being made to

develop toxicologically safe smoke flavors. To achieve

this, flavor technologists world-wide have attempted

to split the smoke condensate into a number of sub-

divisions. Using a variety of countercurrent tech-

niques, the fractions obtained are then examined

to establish the elimination of PAH. Of all of the

chemical constituents of smoke – alcohols, aldehydes,

ketones, phenols, amines, tar, and cresol resin – it is the

PAH typified by benzo[a]pyrene that are known to be

carcinogenic and have thus attracted the most medical

attention. Techniques are now known that can meas-

ure PAH down to 0.001 p.p.m. (See Amines; Carcino-

gens: Carcinogenic Substances in Food: Mechanisms;

Flavor (Flavour) Compounds: Production Methods.)

0014Opinions still differ as to which of the chemical

constituents produce the characteristic smoke flavor.

A study of the oil-soluble fraction of smoke conden-

sate has been made by gas–liquid chromatography.

After purification by extraction, the smoke flavor has

been shown to contain some 20 different aromatic

components, most of which are phenolic in nature.

A few aromatic aldehydes have also been shown to be

present (Table 7).

0015Organoleptic studies of the individual components

or group of components showed cis-iso-eugenol, 2,6-

dimethoxyphenol and 2,6-dimethoxy-4-methylphe-

nol to be the compounds contributing most markedly

to the characteristic smoky flavor. (See Sensory Evalu-

ation: Taste.)

0016Optimum flavor characteristics can only be

achieved by applying proper concentrations using ap-

propriate technology. The concentration required to

achieve the optimum flavor development depends on

the type of product, its fat content, and the processing

method. Examples of concentration of smoke flavor

using one such commercially available preparation

are: ham 45 p.p.m., bacon 32 p.p.m. (in both cases,

added to brine), and sausages, cod roe, fish paste, and

fish sausages 15–45 p.p.m. The object of conventional

smoking is to increase the shelf-life of the product. It is

thus imperative to ascertain what effect application of

smoke flavor or liquid smoke has on the keeping

qualities of the product. Recent research indicates

that 2,6-dimethoxy-4-hydroxybenzaldehyde, one of

the active components of smoke flavor, has marked

antioxidative and antibacterial properties.

Application of Smoke Flavors

0017The flavor components are available in three physical

forms: aqueous, oil-soluble, and dry. They may be

applied to products by any of the following methods

based on their suitability.

0018Spinning head spray system This method utilizes a

variable-speed air motor that spins an atomizing disk

at between 1000 and 18 000 rpm, creating a very fine

atomization. The liquid is fed to the gun via an air-

operated vernier-controlled pump, and an electro-

static charge is applied at the gun tip. This system

can be used for spraying aqueous solutions of smoke

extracts and flavor on to bacon, ham, and chicken,

and in a solvent-based form on to a product such as

salmon, where little or no water is required.

tbl0007 Table 7 Composition of a synthetic smoke aroma

Percentage Level

Furfural 0.17 0.05–0.8

Valeraldehyde 0.002 0.002–0.05

Dihydroxiaceton 0.0012 0.003–0.004

Diacetyl 0.0002 0.0001–0.001

Acetic acid 0.9 0.2–1.5

Formic acid 0.06 0.01–0.1

Propanoic acid 0.14 0.03–0.25

Butyric acid 0.016 0.001–0.03

Valeric acid 0.06 0.01–0.1

Caproic acid 0.008 0.003–0.05

Caprylic acid 0.006 0.001–0.01

Guaiacol 0.001 0.0002–0.01

o-Cresol 0.001 0.0002–0.01

Hexylamine 0.00016 0.00005–0.0008

Ethylamine 0.00016 0.00005–0.0008

tbl0006 Table 6 Composition of a smoke condensate

Fractions Percentage of the

whole condensate

Formaldehyde 0.12

Aldehydes of higher molecular weight 0.57

Ketones 0.67

Formic acid 0.38

Acetic acid and acids of higher molecular

weight

1.71

Methanol 0.96

Tar 4.81

Phenols 0.07

Residue 4.21

Water 82.42

Total 95.92

Extracts from activated charcoal 4.08

SMOKED FOODS/Applications of Smoking 5313

0019 Airless spray system An airless pressure pump feeds

the liquid through a spray nozzle. The electrostatic

charge is applied by a probe at the spray tip. Various

spray nozzle designs are available for achieving the

desired pattern of application. Applications of this

technique are in aqueous systems – extracts in brine

solutions that allow smoking and curing of fish

products in a single operation.

0020 Powder spraying Powder flavors are obtained by

mixing the flavor components with dextrose or starch

base. The application system consists of a powder

hopper and spray gun. The hopper has two regulators

to control air supplied to a Venturi pump and to the

air fan of the gun; a third regulator controls the degree

of vibration at the base of the hopper. The gun has

interchangeable heads that allow for variation of the

spray pattern.

0021 Flavor coating of savory snacks This system incorp-

orates positive charging of the product and negative

charging of the flavor medium. The plant consists of

variably controlled fluidized bed vibrator feeding the

flavor over a knife edge where it picks up a negative

chargeandprojectsitintoastreamofpositivelycharged

product falling freely into the air. Thus, the flavor ad-

heres all around the fallingproduct. In addition tothese

high-tech systems, smoke flavors, brined or unbrined,

can be injected directly to the product and absorbed

during curing in massaging machines and tumblers.

The advantage of this technique is that it simplifies

application and improves control and hygiene.

0022 It has been shown that water-based as well as salt-

based smoke flavors can be used in the production of

sausages and other comminuted meat products. They

are ideal for pork, beef, horse meat, and reindeer

meat. In the fish industry, smoke flavor is successfully

used in the preparation of fish pastes, sausages,

caviar, roe, and sprats. Smoke flavor is also applied

to processed cheeses. It is reported that panelists

could not differentiate between traditionally smoked

and cheese to which smoke flavor had been added.

0023 In canned products, smoke flavor can be added

directly to the oil, thus enabling flavor penetration

during heat processing of already sealed cans.

Technology of Smoking Fish, Meat, and

Cheese

Fish

0024 Operations necessary for production of smoked fish

will depend on species, consumer preference, and

product specification. However, the general proced-

ure is as follows. Fresh grade A fish should always be

used. They are washed to remove scales and surface

lime, etc., and gutted and headed if required. The

belly cavity is cleaned to remove traces of blood and

bellywall lining. Fish are then usually brined before

smoking. Brining is recommended on grounds of

safety. It is recommended that to exclude Clostridium

botulinum completely, fish should be brought to an

internal temperature of 82



C for 30 min during

smoking if 3.5% brine solution is used, or 65



C for

30 min with 5% brine. (See Clostridium: Occurrence

of Clostridium perfringens; Fish: Processing.)

0025After brining, fish are suspended or laid horizon-

tally on racks in the smoking kilns. If equipment

permits, smoking may be carried out in stages, for

example, initially at 30



C for 60 min, followed by



C for 30 min, and finally at 80



C for 2 h or

more until the product has attained the required

color and texture (Table 8).

0026Cold smoking of fish is commonly practiced on the

leaner varieties of fish such as cod or haddock and may

utilize traditionalor liquidsmoke. Depending upon the

type of smoke, brined or unbrined fish is drenched with

a suitable quantity of liquid smoke, which is then

allowed to drain before being put through a drier to

remove the excess moisture if long-term storage is en-

visaged. Nowadays, after addition of smoke, the fish

may be vacuum-packed or refrigerated for transport

to the point of sale. Virtually all types of fish may be

smoked. The most popular varieties in the UK are

smoked herrings (kippers), haddock, mackerel, and

sprats. Smoked salmon is a great delicacy.

Meat

0027Common salt is the basic curing ingredient, although

other compounds such as sugar, nitrite, and/or nitrate

may also be added. (See Meat: Preservation.)

Salt in Cures

0028Salt is the basic ingredient necessary to all curing

mixtures. It dehydrates and alters the osmotic pres-

sure. It inhibits mold growth and subsequent bacterial

spoilage. Its use tends to give a hard, dry, salty prod-

uct that is not very palatable. It is therefore generally

used in combination with nitrite/nitrate. A 65%

‘pickle’ cure is the most popular strength used for

meats. (See Curing.)

Sugar in Cures

0029The addition of sugar is primarily for flavor. It also

moderates the harshness of salt. During cooking, it

forms browning products that enhance the flavor of

cured meats.

5314 SMOKED FOODS/Applications of Smoking

Nitrite and/or Nitrate in Cures

0030 The addition of nitrates and/or nitrites offers the

following advantages: (1) stabilization of the colour

of lean tissue; (2) contribution to the characteristic

flavor of the cured meats; (3) inhibition of growth of

spoilage organisms, thus reducing the risk of food

poisoning; (4) retardation of development of rancid-

ity in the fatty constituents of the meats.

0031 The processes of traditional smoking of meats may

vary, but the general principles are the same. Prime

quality meats are trimmed of most excess fat and then

cured in a curing mixture (containing salt, nitrates

and nitrites in water) for anything up to 7–10 days

at 1–4



C; meats may be pump-injected with curing

mixtures before being smoked in a traditional wood-

chip smoker for several hours. Depending upon the

temperature of smoking, they may be cooked further

in an oven until they are judged to be just right.

Appropriately sized pieces may then be vacuum-

packed and transported to the point of sale.

0032 Nowadays, cured meats may be cooked in a mix-

ture of liquid smoke before being packed, but evidence

suggests that consumers prefer the traditionally

smoked product and are prepared to pay more for it.

0033 The most popularvarieties of smoked meat products

include the well-known hams, beef, horse,and reindeer

meats. In addition, smoked poultry, turkey, and a var-

iety of game birds can be found in specialist delicates-

sen shops. A number of different types of smoked meat

sausages are available throughout the world.

Cheese

0034 Certain varieties of cheeses, e.g., Seretpenir (Iran),

Caramakase (Germany), Bandal (India), and Vol-

godski (Russia), are traditionally smoked. They may

be smoked by hanging in a smoke-charged atmos-

phere without the necessity for higher temperatures.

Both oak and applewood shavings may be used for

smoke generation. Nowadays, incorporation of liquid

smoke is becoming popular. The smoke preparation

may be added to the milk or sprayed on to the curds

before pressing. Occasionally, smoke flavor with salt

may be applied as a spice. In another method of

preparation, cheese is enclosed in a permeable mem-

brane and immersed in a solution of smoke liquor.

0035Traditional smoking brings fat to the surface of the

cheese, evaporates moisture, and incorporates smoke

vapors containing phenolic substances that aid in

giving a preservative effect as well as imparting a

savory flavor to the cheese. The fat on the surface is

also a deterrent to mold growth if the cheese is kept dry.

See also: Amines; Antioxidants: Natural Antioxidants;

Carcinogens: Carcinogenic Substances in Food:

Mechanisms; Clostridium: Occurrence of Clostridium

botulinum; Curing; Drying: Theory of Air-drying; Fish:

Processing; Flavor (Flavour) Compounds: Production

Methods; Meat: Preservation; Phenolic Compounds;

Polycyclic Aromatic Hydrocarbons; Sensory

Evaluation: Taste