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surface exposure, between the alcoholic liquid under-

going acetification and the ambient air. The passage

of oxygen from the gaseous to the liquid phase is

thereby accelerated and intensified and the acetifica-

tion time, which with traditional methods is rather

long, is reduced.

0016 Generator processes, first introduced in Germany,

have been in general use for more than 100 years. The

generator tanks are generally made of wood or some-

times steel, are equipped with cooling coils, and are

vented to allow the air to circulate; they have a per-

forated false bottom which serves to support the

wood shavings (preferably beech) or grape stalks

with which the tanks are filled. A spray mechanism

distributes the alcoholic liquid over the surface of the

packing (Figure 3). The liquid trickles over the wood

shavings covered with Acetobacters and then is

pumped back to the sprinkler header-tank and the

cycle is repeated. The process continues until acetifi-

cation is complete, which generally takes about a

week providing the temperature is kept in the optimal

range of 27–30



C. A measured volume of vinegar is

then withdrawn from the bottom of the tank and is

replaced with an equal volume of fresh liquid. The

generator process is a continuous process which gives

a fairly clear vinegar with good sensory characteris-

tics. However, it is slow and about 20% of yield is lost

through evaporation. Also, the wood shavings have

to be replaced at least once a year.

0017The third category involves the submerged pro-

cesses. These are the most up-to-date, benefitting as

they do from industrial experience with submerged

culture techniques employed in the field of antibiotics.

These processes do not use wood shavings, but air

forced into the liquid, and the mother of vinegar is

often replaced with selected cultures of Acetobacters.

The generator tank is made of stainless steel, or poly-

propylene reinforced with fiberglass; it is equipped

with devices to insure an adequate and continuous

flow of air, with cooling coils which maintain a steady

temperature of about 30



C in the fermenting body of

liquor, with thermometers for monitoring temperature

and, sometimes, with an automatic gage for measuring

the alcohol content of the fermenting liquid. Oxida-

tion of the alcohol is started slowly by means of aer-

ation, and fermentation is apparent after about 24 h.

Air is then introduced at regular hourly intervals; it

permeates the body of liquor in a uniform manner,

causing rapid and lively fermentation. Acetification

is deemed complete when the residual alcohol is

around 0.2–1.5% w/v (depending on the type of vin-

egar required). The process is extremely rapid. About

half of the resultant vinegar is then withdrawn; the

remaining vinegar acts as mother for the next batch.

0018This method was first developed in the USA and

Germany. It spread rapidly throughout the world and

displaced the older, slower processes. The yield is very

high (90–95%), since there is little loss through evap-

oration. However, the product is rather cloudy and less

aromatic than vinegars obtained by slower fermenta-

tion processes. This is due to the fact that, given the

brief period of contact, the esterases do not have time

to perform their function adequately and the charac-

teristic volatile substance content is low as a result.

0019The product is therefore filtered and, in some cases,

put into wooden casks to age; the result is a vinegar of

superior quality which is rich in biological principles,

generated by bacterial-cell autolysis, and perfectly

clear.

0020Malt vinegar Malt vinegar, which is the most

common variety in UK, is produced without inter-

mediate distillation from the double fermentation (al-

coholic and acetous) of malted barley with or without

the addition of other cereals, the starch of which

has been converted into fermentable sugars from

a-amylase of malted barley.

0021Malt vinegar manufacture involves mashing, fer-

mentation, and acetification. During mashing, the

malted barley, sometimes mixed with other cereals

such as maize and rice, is milled and mixed with hot

water in mash tuns, where the starch is converted

by a-amylase into maltose, dextrose, and dextrins.

The sweet liquor drains off the mash through the

fig0003 Figure 3 Circulating generator: A, sprinkler for dispersal of the

liquidoverthewoodshavings;B,beechwoodshaving;C,perforated

false bottom; D, tap for withdrawal of the liquid; E, thermometers.

5998 VINEGAR

perforated false bottom of the tun and is collected in

vessels where it is fermented by the addition of yeasts,

which convert the fermentable sugars to ethanol and

carbon dioxide. When fermentation is practically

complete, the alcoholic liquor is separated from the

yeasts and acetified by inoculation with Acetobacter

cultures. The resultant alcohol is thus oxidized to

acetic acid in the presence of atmospheric oxygen.

The process lends itself to the different systems in

current use. The vinegars will be more or less aro-

matic, the superior varieties will be those produced by

the old and slow Orleans process.

0022 Malt vinegar is straw-colored and must in any case

contain 4% w/v of acetic acid. Distilled malt vinegar

is prepared by distilling malt vinegar. This product

contains only the volatile constituents of the original

vinegar and is colorless; it is generally used for the

preparation of pickled silverskin onions. (See Malt:

Chemistry of Malting.)

0023 Wine vinegar Wine vinegar, which is obtained from

acetous fermentation of wine, is largely produced in

continental Europe.

0024 The wines used for acetification are those with too

low an alcohol content (7–9% v/v) or those in which

volatile acidity is too high. Spoilt wines cannot be used.

If wines with a high alcohol content are to be used, they

need to be appropriately diluted with water, since a

high concentration of alcohol will inhibit the develop-

ment of the Acetobacters. For the same reason, the

wine must be free of sulfur dioxide and dregs.

0025 Both white and red or rose

wines can be used to

produce white or red vinegar, respectively. In the

domestic or small-scale production of wine vinegar,

the wine is poured into small wooden barrels,

together with the vinegar mother, which consists of

colonies of Acetobacters taken from barrels in which

vinegar has already been produced. The barrel must

contain air, so for this reason it is not filled com-

pletely. Acetification is slow and stops spontaneously

when acidity reaches 7–8%. The slow transformation

of wine into vinegar leads to the formation of many

substances which impart excellent organoleptic qual-

ities to the end product. The most important of these

are acetaldehyde and ethyl acetate – which in top-

grade vinegars are present in quantities far greater

than those of wine – volatile alcohols, particularly

3-methyl-1-butanol, and 3-hydroxy-2 butanone (or

acetylmethylcarbinol).

0026 The vinegar is then partly withdrawn for use and

replaced with fresh wine to be acetified. Vinegar pro-

duced in this way is bound to vary in composition and

character: it may be more or less cloudy and its

acidity may vary according to the degree of alcohol

in the wine and the nature of the fermentation.

0027However, most wine vinegar is produced by indus-

trial processes and, as such, is a standardized indus-

trial product; according to EC regulations, its total

acidity must not be less than 6 g of acetic acid per

100 ml and residual ethanol may be present in quan-

tities not exceeding 1.5% v/v. The color varies from

pale yellow to red, depending on the wine used; the

clear vinegars made from white wine are in great

demand for pickling. (See Wines:Types of Table Wine.)

0028Cider vinegar Cider vinegar is prepared from apple

wine that has undergone acetous fermentation and is

widely used as a table vinegar, above all in the USA

and UK. It is yellowish in color and may be darkened

with caramel. Its acidity is not very high and its

acidic, astringent flavor recalls the fruit of origin.

(See Cider (Cyder; Hard Cider): The Product and its

Manufacture; Chemistry and Microbiology of Cider-

making.)

0029Fruit vinegars Fermented juices from other fruits

such as peaches and berries are also used to produce

vinegar. Since these alcoholic liquids are not distilled,

they maintain the subtle flavors and aromas of the

raw ingredients; this confers on the vinegars much-

appreciated characteristics.

0030Rice vinegar In the Far East, where rice is the staple

cereal, vinegar is prepared from rice as such, from

sake (its fermentation product), or from the by-

products of sake manufacture. Traditional methods,

similar to the Orleans process, are still in use but have

been largely superseded by modern submersion tech-

niques. This vinegar has a fairly low acidity and a

high amino acid content. It is light in color and has a

clean, delicate flavor. It is therefore highly prized in

oriental cooking since it does not significantly alter

the taste of the food; it is excellent for flavoring with

herbs, spices, and fruits because of its mild flavor.

0031Molasses vinegar This vinegar is prepared from

sugar syrup or molasses by double fermentation, al-

coholic fermentation of sugars, and the subsequent

acetic bioxidation. It serves to make use of the by-

products of the sugar industry, but is not widely used.

0032Honey vinegar This vinegar is obtained from honey

which is added to the right quantity of water, sub-

jected to alcoholic fermentation so as to obtain a

drink containing ethanol (mead), which, at the right

temperature and in the presence of oxygen is subject

to the action of acetic bacteria so as to obtain acetic

acid. The vinegar is then clarified by bland filtration

or by decanting, so that all the qualities of honey

remain unaltered.

VINEGAR 5999

0033 Spirit vinegar Spirit vinegar, sometimes referred to

as white, distilled, or alcohol vinegar, is prepared

by acetous fermentation of an alcoholic distillate

obtained from the products of alcoholic fermentation

of natural sugar solutions. In countries where it is

permitted by law, wide use is made of synthetic etha-

nol, diluted to 10–14% v/v. Spirit vinegar is colorless

and is often colored with caramel; it is strongly acid

but not aromatic; the distillation of the alcoholic

liquids increases the concentration of ethanol, but

reduces flavor. This vinegar is less expensive and is

the most widespread in the world. When diluted to

4–5% acidity it is used for pickling.

0034 Balsamic vinegar A particular type of highly prized

vinegar has been produced for centuries in the prov-

inces of Modena and Reggio Emilia in Northern Italy.

0035 The raw material is grape must, preferably Treb-

biano. When alcoholic fermentation has just started,

about 24 h after pressing, the must is boiled gently

until it has reduced to about one-half or one-third of

its starting volume. The result is a liquor with a high

sugar concentration (about 30%) in which alcoholic

and acetous fermentation take place together ex-

tremely slowly; yeasts (Saccharomyces and Zygosac-

charomyces) and acetic bacteria (Acetobacter and

Gluconobacter) are needed for the formation of this

vinegar.

0036 Traditional balsamic vinegar takes many years to

produce. During the process of fermentation, matur-

ing, and aging, the product becomes highly concen-

trated and the sugars, alcohols, aldehydes, and

organic acids undergo extremely gradual chemical

transformation. The vinegar battery consists of a

variable number of barrels (between five and 12 or

even more) of different woods and decreasing in size.

They are set up in well-ventilated areas which are hot

and dry in summer and cold in winter. According to

the traditional method, part of the contents of the

smallest barrel is withdrawn annually for consump-

tion, and is replaced with an equal volume from the

next largest barrel in the battery. This is in turn re-

plenished from its neighbor, and so on up the line.

Finally, the largest barrel is topped up with the

season’s boiled must (Figure 4).

0037The process takes at least 12 years, though it is not

uncommon to find vinegars that are 50 or more years

old, and the yield is very low (no more than 1 l of

vinegar from 100 kg of fresh must). The end product,

however, is of exceptionally high quality, dark brown

in color, of a syrupy consistency, sweet and sour to the

taste, and with a characteristically pleasant aromatic

smell. In traditional balsamic vinegar the total solids

are very high (20–70%), acidity varies between 6 and

18% w/v acetic acid and there are large amounts of

sugars, essentially glucose and fructose, as well as

numerous aromatic substances that have gradually

been formed over the years.

Chemical Synthesis

0038Acetic acid is usually synthesized by catalytic oxida-

tion from acetaldehyde. Acetaldehyde is in turn

obtained by catalytic hydration of acetylene or by

catalytic dehydrogenation of ethanol (Figure 5).

Formic acid and formaldehyde, byproducts of acetic

acid synthesis, are removed by distillation.

0039The acetic acid is subsequently purified and diluted

with water to 60–80% by volume to obtain the

6th

operation

Oak

60 l

5th

operation

Chestnut

50 l

4th

operation

Cherry

40 l

3rd

operation

Ash

30 l

2nd

operation

Mulberry

20 l

1st

operation

fig0004 Figure 4 Battery of barrels for manufacture of the ‘traditional balsamic vinegar of Modern’.

6000 VINEGAR

‘vinegar essence.’ In order to produce a food-grade

vinegar, this ‘vinegar essence,’ which is a concentrated

solution of acetic acid and highly corrosive, is further

diluted until it contains 4–5% w/v of acetic acid. This

liquid is used in the preparation of synthetic vinegar.

0040 Synthetic Vinegar A number of countries allow a

nonfermented vinegar to be used for alimentary pur-

poses which may be produced using synthetic acetic

acid that is diluted, aromatized, and colored. The

synthetic vinegar thus obtained needs to be colored

artificially, and for this purpose caramel is commonly

used. It is then aromatized with the addition of

sugars, chemical seasoning, and salt or with the

addition of natural vinegar. The end product must

contain at least 4% w/v of acetic acid, as in the case

of fermented vinegars. However, the name ‘vinegar’ is

not always accepted for this product; in the UK for

example, it must be labeled ‘nonbrewed condiment.’

Characterization and Analysis of Vinegars

0041The relative density of vinegars ranges from 1.007 for

synthetic vinegars to 1.360 for balsamic vinegars.

Total solids and ash vary according to type. They

are very high in the ‘traditional balsamic vinegar of

Modena.’ They are more abundant in malt, wine, and

cider vinegars than they are in spirit vinegars and

synthetic vinegars.

0042Brewed vinegars, being a natural product, contain

a large number of components that may derive from

the raw materials, be the result of primary or second-

ary fermentation, or derive from the interaction of

components from these two sources (Table 1).

0043The most abundant volatile constituent is acetic

acid, which is largely responsible for the acidity of

the vinegar. It ranges from 4–5% for rice vinegars to

10–12.5% for distilled vinegars.

0044The presence of acetaldehyde, a byproduct of acet-

ous fermentation, is typical. Numerous esters, major

contributors to aroma, are present, notably ethyl

acetate, the major portion of which was formed

during storage, and also methyl and isopentyl acetate;

various isomeric butanols and pentanols, present in

the raw material, occur in vinegars.

0045The formation of 3-hydroxy-2-butanone and 2,3-

butanedione are typical, deriving from 2,3-butandiol,

HC CH

CCH

−H

O x

fig0005 Figure 5 Chemical syntheses of acetic acid.

tbl0001 Table 1 A comparison of some typical figures for the chemical composition of various vinegars

Malt

vinegar

Wine

vinegar

Cider

vinegar

Spirit

vinegar (conc.)

Rice

vinegar

Balsamic

vinegar

Synthetic

vinegar

Relative density (20



) 1.013–1.022 1.013–1.020 1.013–1.024 1.015–1.020 1.042–1.361 1.007–1.022

Total solids (g l

 1

) 3.00–28.40 8.71–24.88 19.00–35.00 1.50–6.00 336.70–873.90 1.00–4.50

Total ash (g l

 1

) 0.60–7.60 1.47–3.10 2.00–4.50 0.20–0.50 0.50–7.60 4.00–18.80 0.20–0.50

Alkalinity of ash (mmol l

1

) 9.60–31.60 26–152

Total acidity as acetic acid (%) 4.30–5.90 5.94–9.20 3.90–9.00 11.50–12.20 4.00–5.24 6.25–14.88 4,10–5.30

Volatile acidity as acetic acid (%) 5.55–7.95 3.79–5.16 3.90–13.60

Fixed acidity as acetic acid (%) 0.20–0.40 0.02–0.55 0.10–0.20 0.05–0.66 1.58–2.27 Negligible

Alcohol (% v/v) 0–0.14 0–0.81 0.03 0.15 0–0.68 0.04–0.08

Total nitrogen (g l

1

) 0.40–1.40 1.15–1.86 0.03–0.30 0.80–1.29 1.02–2.16 0–2.00

Sugars (g l

1

) 0–6.20 1.50–7.00 0–91.00 351.00–689.70

Glycerol (%)

0.37 0.28 0.94–1.7

Gluconic acid (%)

0.02 0.02 0.68–1.14

Tartaric acid (%)

0.11 0.46–0.52

Acetic acid (%)

7.2 5.5 6.38–7.64

Citric acid (g l

1

) 0.26–0.39 1.66–3.47

Malic acid (g l

1

) 0.47–0.80 0.70–1.60 8.00–37.40

Acetaldehyde (mg l

1

) 18.9–114.4 84.9–374.7

2,3 Butanediol (mg l

1

) 470–2890

2,3 Butanedione (mg l

1

) 17–37

3 Hydroxy-2 butanone (mg l

1

) 122.0–1257.0 249.1–1597.8

Ethylacetate (mg l

1

) 206.0–590.0

Data from Egan H, Kirk RS and Sawyer R (1987) Pearson’s Chemical Analysis of Foods, 8th edn. Harlow: Longman Scientific and Technical.

Data from Stella C (1976) La composizione degli aceti Vini d’Italia 18: 269.

Data from Mizumoto H, Minamisone H, Mori K and Azumo K (1975) Chemical composition of commerical rice vinegars. Kagoshima-ken Kogjo Shikenjo

Nempo 22: 67.

Data from Plessi M and Coppini D (1984) L’aceto balsamico tradizionale di Modena. Atti della Societ

dei Naturalisti e Matematici 115: 39–46.

Data from Giudici P et al. (1994) Origine ed evoluzione degli acidi organici durante l’invecchiamento dell’aceto balsamico. Industria delle bevande

23: 569–574.

VINEGAR 6001

a product of the condensation of acetaldehyde by

microorganisms, which are always, and only, found

in brewed vinegars, albeit in variable quantities

(Table 2).

0046 Organic acids, other than acetic acid, are also pre-

sent: tartaric and citric are largely found in wine

vinegars, while formic and malic acid are those most

commonly found in cider vinegars. During the

fermentation process small quantities of other acids,

such as succinic acid, lactic acid, and fumaric acid,

are formed.

0047 Of the many analyses that vinegars lend themselves

to, the most useful from the point of view of general

characterization are the following:

0048 Sensory examination: The sensory characteristics

to be taken into account are color, odor, and taste,

which must conform to those attributed to the type

of vinegar being analyzed. If the vinegar is cloudy,

it must be examined under strong magnification for

vinegar eels (Anguillula aceti), a nematode that is a

typical parasite of vinegar.

0049 Relative density: This is determined at 20



C using

a Westphal balance or pyknometer.

0050 Total acidity: This is determined by titrating the

diluted product with a standard alkaline solution.

It is expressed as grams of acetic acid per 100 ml of

vinegar.

0051 Fixed acidity: A 10-ml aliquot of vinegar is evapor-

ated to dryness and reconstituted with water, the

process being repeated in order to eliminate acetic

acid. The final residue is dissolved in water and

titrated with an alkaline solution. It is expressed

as grams of tartaric acid per 100 ml of vinegar.

0052 Volatile acidity: This is calculated from the differ-

ence between total and fixed acidity, both expressed

as grams of acetic acid per 100 ml of vinegar.

0053Total solids: A 50-ml aliquot of vinegar is evapor-

ated in a platinum capsule with water in order to

eliminate the acetic acid. It is then dried to constant

weight in an oven at 100



0054Ash: The total solids are ignited at 500–550



C. If a

high ash figure is obtained, salt should also be

determined.

0055Ash alkalinity: This is chiefly due to potassium

carbonate formed during calcination and is deter-

mined by dissolving the ash in an exact quantity

of standard sulfuric acid, of which the excess is

titrated with alkali. It is expressed in mmol of alkali

per liter.

0056Ethanol: A 100-ml aliquot of vinegar is neutralized

with sodium hydroxide and double-distilled. The

density of the solution is measured and, conse-

quently, the quantity of ethanol is calculated from

tables.

0057Total nitrogen: This is determined by the Kjeldahl

method on 25 ml of vinegar.

Methods of Differentiating Between Various Types

of Vinegar

0058Apart from color and odor, the nitrogen, phos-

phates, ash, and their alkalinity also serve to differen-

tiate between the various types of vinegar. In a

malt vinegar, nitrogen and phosphate figures are

low, while in a rice vinegar the nitrogen figure

is higher and distilled vinegar has a very low ash

content.

0059However, useful methods of routine differentiation

are based on those values that depend on the volatile

substances present, namely:

0060Oxidation value: The number of ml of 0.002

mol l

1

KMnO

discolored by 100 ml of sample in

30 min under standard conditions. Alcohol and

tbl0002 Table 2 A comparison of major volatile components of various vinegars

Malt vinegar Wine vinegar Cider vinegar Distilled vinegar Balsamic vinegar

Ethyl acetate Acetaldehyde Acetaldehyde Acetaldehyde Ethyl acetate

Ethyl formate Ethyl acetate Ethyl acetate Ethyl acetate Ethanol

3-Methyl-1-butanol Ethyl formate Ethyl formate Ethyl formate 3-Hydroxy-2-Butanone

2-Methyl-1-propanol 2-Methyl-1-propanol 3-Methyl-1-butanol Ethanol 2,3-Butanediol

2-Methyl-1-butanol 3-Hydroxy-2-butanone 2-Pentanol 2-Pentanone 2,3-Butanedione

Acetaldehyde 2,3-Butanediol 2-Methyl-1-butanol 3-Pentanol Methyl acetate

Ethanol 3-Methyl-1-butanol 2-Methyl-1-propanol 2-Pentanol Acetaldehyde

Isobutyl acetate Isopentyl acetate Ethanol Methyl formate Furfural

Isopentyl formate 2-Methyl-1-butanol 2-Pentanone Propionaldehyde 2,4,5-Trimethyl-1,3-dioxolane

Isopentyl acetate Ethanol 3-Pentanol Methanol Acetone

Benzaldehyde Isovaleraldehyde Benzaldehyde Acetal 3-Methyl-1-butanol

Acetone Isobutyl acetate Propionaldehyde 2-Methyl-1-butanol Ethyl formate

Isobutyl formate g-Butyrolactone Ethyl lactate 3-Methyl-1-butanol Isobutanal

2-Pentanone Acetone Phenylacetaldehyde 2-Methyl butanal

2-Methyl-3-buten-2-ol Isobutyl formate Diethyl succinate 2-Butanone

2-Pentanone Furan

6002 VINEGAR

acetylmethylcarbinol are mostly responsible for the

oxidation value.

0061 Iodine value: The number of ml of 0.01 mol l

1

iodine absorbed by 100 ml of sample under stand-

ard conditions. This value is mostly influenced by

acetylmethylcarbinol and diacetyl.

0062 Ester value: The number of ml of 0.01 mol l

1

KOH required to saponify the esters contained in

100 ml of sample under standard conditions.

0063 Brewed vinegars give comparatively high values,

but those for artificial products are low as the latter

are almost devoid of volatile reducing substances.

0064 Vinegars can be more specifically identified by

means of gas chromatography. This technique can

distinguish brewed vinegar from synthetic vinegar

and also brewed vinegars from different origins by

analyzing the accompanying compounds (metabolic

byproducts of Acetobacter strains and substances

derived from the raw material).

0065 In addition, the blending or adulteration of brewed

vinegar with synthetic acid can be detected by mass

spectrometric determination of the

C-isotope

ratio; brewed vinegar has 5% more

C isotope than

acetic acid synthesized petrochemically.

Food Uses

0066 Vinegar has long been used worldwide as a basic

seasoning in the preparation and cooking of certain

foods, because its sharp taste makes it so useful and

versatile.

0067 A considerable quantity of vinegar is marketed as

such for domestic use. In the UK and USA the table

vinegar most widely used is cider vinegar, while in

Ireland it is malt vinegar and, in grape-growing coun-

tries, such as Italy, France, and Spain, wine vinegar.

In the Far East, in addition to the traditional rice

vinegar, synthetic vinegar is very common.

0068 Vinegar adds flavor to vegetable and meat prod-

ucts. It is one of the ingredients of salad dressings,

sauces, such as tabasco, and tomato products, such as

ketchups, mustard, and aspics. Mixed with oil and

salt it makes the classic vinaigrette, and it can be used

as a condiment for salad and as a sauce for cold,

cooked vegetables, meat, and fish.

0069 For condiment uses, vinegar can be aromatized

with herbs and spices like tarragon, basil, garlic, shal-

lot, and elder. They are steeped in the vinegar when

acetification is complete; in certain types of vinegar

sugars are added as well. These vinegars add special

and unusual tastes to food.

0070 The aroma and sweet and sour flavor which bal-

samic vinegar confers on foods to which it has been

added is decidedly particular; it is suitable for all

types of food, such as sauces, green salads, and meat

and sprinkled on strawberries, peaches, or melon

adds a pleasant flavor and aroma.

0071Finally, because of its acetic acid content and low

pH, vinegar is used as a preservative for both domes-

tic use and in the food industry. It is in fact used for

the preservation, or pickling, of a wide variety of

foods such as vegetables, meat, fish products, and

spiced fruits. For this purpose, the food-processing

industry uses mainly distilled vinegar and, where the

law permits, synthetic vinegar.

See also: Acids: Properties and Determination; Natural

Acids and Acidulants; Preservatives: Classifications and

Properties; Spices and Flavoring (Flavouring) Crops:

Use of Spices in the Food Industry

Further Reading

Adams MR (1985) Vinegar. In: Wood BJB (ed.) Microbiol-

ogy of Fermented Foods, pp. 1–47, vol. 1. Essex: Elsevier

Applied Science.

AA VV (1996) L’aceto Balsamico di Modena. Modena:

Consorzio Tutela Aceto Balsamico di Modena.

Carnacini A and Gerbi V (1992) L’aceto di vino, un pro-

dotto da valorizzare e tutelare. Industrie delle Bevande,

19: 465–483.

Conner HA and Allgeier RJ (1976) Vinegar: its history and

development. Advances in Applied Microbiology 20:

81–133.

Coppini D, Plessi M and Monzani A (1978) Ulteriore

contributo allo studio dell’aceto Balsamico. Rivista di

Viticoltura ed Enologia 31: 351–357.

Egan H, Kirk RS and Sawyer R (1987) Pearson’s Chemical

Analysis of Foods, 8th edn. Harlow: Longman Scientific

and Technical.

Garcı

´a-Parrilla

MC, Gonza

les GA, Heredia FJ and Trocoso

AM (1997) Differentiation of wine vinegars based on

phenolic composition. Journal of Agriculture and Food

Chemistry 45: 3487–3492.

Garoglio PG (1973) Enciclopedia Vitivinicola Mondiale.

Milano: Edizioni Scientifiche UIV.

Masai H (1980) Recent technical developments on vinegar

manufacture in Japan. Proceedings of the Oriental

Fermented Foods 192–198.

Mizumoto H, Minamisone H, Mori K and Azumo K (1975)

Chemical composition of commercial rice vinegars.

Kagoshima-ken Kogyo Shikenjo Nempo 22: 67–68.

Nieto J, Gonza

-Vin

as MA, Barba P et al. (1993) Recent

progress in wine vinegar R & D and some indicator for

the future. In: Charalambous G (ed.) Food Flavours,

Ingredients and Composition, pp. 469–500. Amster-

dam: Elsevier Science.

Plessi M and Coppini D (1984) L’aceto balsamico tradizio-

nale di Modena. Atti della Societa

dei Naturalisti e

Matematici 115: 39–46.

Plessi M, Monzani A and Coppini D (1987) Determination

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VIRUSES

H Appleton, PHLS Central Public Health Laboratory,

London, UK

Background

0001 Viruses are usually transmitted directly from person

to person, but it is clearly recognized that, on occa-

sions, some viruses may also be transmitted by foods

and water. Unlike bacteria, viruses do not multiply or

produce toxins in food: food items merely act as

vehicles for their passive transfer. Any virus that is

infectious via the gastrointestinal tract could be con-

sidered a potential foodborne pathogen, but in prac-

tice, the most commonly reported foodborne viral

infections are gastroenteritis and, less frequently,

hepatitis. Although the clinical characteristics of

these two illnesses differ, their food-related mode

of transmission is essentially the same. Foodborne

spread of both these infections has been clearly de-

fined, but the extent of the problem is unknown. For

various reasons, the incidence of both is almost

certainly under-reported.

Viral Gastroenteritis

0002 Gastroenteritis is the most common foodborne viral

infection. Discovery of the viruses responsible for

causing gastroenteritis began with the identification

of the Norwalk virus in 1972 and then the human

rotavirus in 1973. These viruses are usually transmit-

ted directly from person to person via the fecal–oral

route. In 1977, however, there was a report that a

virus had been responsible for a community-wide

outbreak in England associated with shellfish. At

least 800 people were affected, and it is now clearly

established that food may also play an important role

in transmission.

0003 Prior to the discovery of gastroenteritis viruses and

recognition of their foodborne mode of transmission,

there were many reports of ‘food poisoning outbreaks

of unknown etiology,’ which were assumed to be

bacterial but in retrospect have the characteristics of

viral gastroenteritis. Such reports still occur when

appropriate viral investigations are not undertaken.

Viral gastroenteritis tends to mimic bacterial food

poisoning, and invariably, outbreaks are initially in-

vestigated for traditional food poisoning bacteria.

However, there are characteristic features that should

alert investigators to the possibility of a viral cause.

The incubation period is somewhat longer and more

variable than for most bacteria, with a peak of

around 30–36 h (range 12–60 h, which may be dose-

dependent). Symptoms are variable and may include

both vomiting and diarrhea as well as the usual range

of associated complaints such as abdominal pain,

general malaise, and nausea.

0004Secondary person-to-person spread is a character-

istic feature. Illness is usually regarded as mild and

self-limiting with recovery within 24–48 h. However,

people commonly feel debilitated for 2–3 weeks, and

this can have considerable impact socially and eco-

nomically in impaired performance. Outbreaks may

be very disruptive and have led to closure of hospitals

and schools. Some outbreaks have been very large,

involving several hundred people. Treatment is not

normally required unless people are severely affected

and become dangerously dehydrated. This is a more

common problem in children suffering diarrheal dis-

eases in underdeveloped countries. Oral rehydration

therapy with simple balanced salt solutions is an

effective treatment.

0005The overall incidence viral gastroenteritis is un-

known. A community-based study of infectious intes-

tinal disease, from all causes in England from 1993 to

1996, confirmed that the vast majority of cases go

unreported. The study found that viruses were re-

sponsible for a far greater proportion of gastrointest-

inal illness than national surveillance figures had

previously indicated. The study also concluded that

infections resulting from viruses are less likely to be

6004 VIRUSES

reported than bacterial infections. It was estimated

that only one in 35 infections with rotavirus and one

in 1562 infections caused by Norwalk-like viruses

occurring in the community are reported to national

surveillance, compared with one in three cases of

salmonellosis.

0006 The proportion of these viral gastrointestinal infec-

tions that is foodborne is similarly unknown. Viruses

account for 6% of foodborne outbreaks and 5%

of waterborne outbreaks occurring in England and

Wales and reported to national surveillance, but this

is likely to be a gross underestimate of the true inci-

dence. The mild nature of the illness means that per-

sons do not tend to consult a medical practitioner.

However, the short incubation period means that

when an illness is investigated, possible association

with a food source is more likely to be recognized

than for hepatitis A, for which there is a long incu-

bation period. The highly infectious nature of the

viruses and the frequent occurrence of secondary

person-to-person spread also add to the difficulties

of identifying a food- or waterborne outbreak.

The Gastroenteritis Viruses

0007 Several different viruses cause gastroenteritis

(Table 1), but it is the viruses of the Norwalk group

that have been particularly linked to foodborne trans-

mission. They form a complex group, and the nomen-

clature is confusing. The viruses have been known

variously as Norwalk-like viruses (NLV), and as

small round structured viruses (SRSV) because of

their appearance when viewed in the electron micro-

scope (Figure 1). The virus particle measures

30–35 nm in diameter and has an amorphous surface

and a ragged outline. They are classified as members

of the Caliciviridae family and hence are sometimes

referred to as human caliciviruses.

0008 Norwalk-like Viruses The Norwalk virus, which

originated from a school outbreak of nonbacterial

gastroenteritis at Norwalk, Ohio, in the USA, was

the first virus of the group to be discovered. Viruses

of this group are frequently the cause of both commu-

nity and institutional outbreaks of nonbacterial gas-

troenteritis, whether resulting from person-to-person

spread or a food or water source. Outbreaks in hos-

pitals, residential homes, schools, hotels, restaurants,

and cruise ships have been reported frequently. The

rapid spread of infection can cause major disruption,

leading to closure of schools and hospital wards.

There are also considerable economic costs in terms

of working days lost. They are probably the most

important cause of sporadic gastroenteritis in the

community, although because of the relatively minor

nature of illness, such incidents are not usually inves-

tigated. In the UK, NLVs have been implicated in

more than 90% of foodborne outbreaks where a

virus has been detected, and it is clear that this virus

group is the main cause of foodborne viral gastroenter-

itis in developed countries.

0009Several different serotypes have been identified.

Immunity to NLVs is poorly understood and may be

short-lived. Volunteer studies have shown that some

tbl0001 Table 1 Viruses commonly causing gastroenteritis

Virus Person-to-person

spread

Food- or

waterborne

spread

Norwalk-like virus

Yes Yes

Rotavirus Yes Infrequent

Astrovirus Yes Infrequent

Adenovirus (types 40 and 41) Yes Not reported

Also known as small round structured viruses.

Food- and waterborne transmission is probably more significant in

underdeveloped countries.

fig0001Figure 1 Electron micrograph of a group of Norwalk-like vir-

uses. The virus particles have an amorphous surface and ragged

outline. Most particles are complete, but an empty stain-

penetrated particle can be seen at the top of the group. Virus

particles negatively stained with phosphotungstic acid. Magnifi-

cation: 200 000.

VIRUSES 6005

people may be infected on more than one occasion by

the same virus. Thus, people who experience several

incidents of illness may not only be infected with

different antigenic types of NLV, but may also

develop illness on more than one occasion from the

same virus.

0010 The development of polymerase chain-reaction

(PCR) assays has allowed the molecular characteriza-

tion of virus strains from many outbreaks. The human

gastroenteritis viruses in the Caliciviridae family form

three broad genogroups. Two groups have the morph-

ology of NLVs (Figure 1) and broadly similar genomic

features. Members of the third group are known as

Sapporro-like viruses (SLVs). The genomic arrange-

ment of this third group is distinct from the other two

groups. In addition, SLVs have the classical morph-

ology more usually associated with the calicivirus

group, with hollow cup-like depressions on the sur-

face, which are not usually seen in NLVs. (The name

calicivirus derives from the Latin calix meaning cup.)

The different serotypes of the human caliciviruses

broadly correspond with the genotypic groups. The

majority of reported infections caused by viruses with

classical calicivirus morphology have occurred in

young children. Outbreaks in nursery groups in-

volving person-to-person transmission have been

recorded. The virus has also observed in older per-

sons, and some reported foodborne outbreaks have

been attributed to calicivirus.

0011 Rotavirus Rotaviruses mainly infect young children

and are the most frequently reported of the gastroen-

teritis viruses. It is estimated that they may cause a

million deaths a year in children under 5 years of

age, mostly in developing countries. In developed

countries, deaths are relatively rare, but rotavirus

gastroenteritis is the most frequent reason for admis-

sion of young children to hospital. Foodborne

and particularly waterborne spread are probably

significant modes of transmission in developing

countries, but in developed countries, reports are

rare. Although rotavirus has been detected in shell-

fish, so far, there have been no reports of illness from

this source.

0012 Astrovirus Astroviruses form a morphologically

distinct group of viruses, and are named from the

five- or six-point star seen by electron microscopy

on the surface of some particles. Astroviruses are

normally associated with gastroenteritis in young

children, often under 1 year of age. There have been

occasional reports of astrovirus infection in some

adults following consumption of shellfish or contam-

inated water, but these incidents appear compara-

tively rare.

0013Adenovirus Adenovirus serotypes 40 and 41 have

been specifically linked to gastroenteritis, and infec-

tions in young children are frequently reported.

Reports in older patients are rare. There have been

no reports of food- or water-associated adenovirus

infection.

0014Parvovirus Parvoviruses are small DNA-containing

viruses. Their role as causative agents of gastroenter-

itis in humans is uncertain, since, unlike other gastro-

enteritis viruses, there is a prolonged carrier state in

some persons. However, parvoviruses are an import-

ant cause of gastroenteritis in some animal species.

Parvoviruses have been observed in school outbreaks

of winter vomiting disease and in a number of shell-

fish associated outbreaks of gastroenteritis. Parvo-

virus-like particles have been detected occasionally

in shellfish that have been implicated in illness and

where a similar virus has been found in patients.

Hepatitis

0015Hepatitis is an inflammation of the liver and is usually

recognized by the occurrence of jaundice. Descrip-

tions of hepatitis can be traced back to the time of

Hippocrates, but it was not until the eighth century

that the infectious nature of the disease was first

mentioned in letters from Pope Zacharias to Saint

Boniface, Archbishop of Mainz. The viral etiology

was first postulated by MacDonald in 1918 and was

later confirmed by volunteer studies in the 1940s. It is

now known that several different viruses may cause

hepatitis, but it is the enterically transmitted viruses,

hepatitis A and hepatitis E, that are of importance in

foodborne and waterborne transmission.

Types of Hepatitis

0016Hepatitis A Hepatitis A is transmitted by the fecal–

oral route and is prevalent in conditions of over-

crowding and poor hygiene. Although it has long

been recognized that hepatitis A may be transmitted

by food and water, the incubation period of 3–6

weeks makes it difficult to link infection to a food

source. Hence, reports of foodborne hepatitis are

infrequent and are unlikely to indicate the true extent

of the problem. Symptoms in addition to, or instead

of, jaundice are nausea and general malaise. Patients

may feel unwell for several weeks, but recovery is

complete; fatalities are rare. There is no specific treat-

ment, but a vaccine is available. Illness tends to be less

severe in children, and in some, infection is symptom-

less. Once infected, a person is immune from further

infection. As hygienic conditions improve, infection

becomes less common in children, and a larger pro-

portion of the adult population becomes susceptible.

6006 VIRUSES

Serological surveys in the UK indicate that only

10–15% of young adults have antibody to hepatitis

A virus (HAV).

0017 HAV is a small, compact icosohedral virus measur-

ing 25–30 nm in diameter. It is classified as a picorna-

virus (from the Latin pico (small) þ rna as it has an

RNA genome). Within the Picornaviridae family, it is

assigned to the hepatovirus genus. There is only one

serotype.

0018 Hepatitis E More recently, another enterically

transmitted form of hepatitis (designated hepatitis

E) has been described. This virus has been associated

with large waterborne outbreaks in some developing

countries, notably in Asia, Africa, and Central Amer-

ica. Illness appears more severe than hepatitis A, par-

ticularly in pregnant women for whom a mortality

rate of 17–34% has been reported. Secondary person-

to-person transmission is estimated at only 0.7–8%.

The primary source of infection appears to be con-

taminated water rather than person-to-person spread.

Cases in the UK are reported infrequently and are

mainly imported from endemic areas.

0019 Hepatitis E is classified as a calicivirus but is ser-

ologically unrelated to the viruses that cause gastro-

enteritis. Like all caliciviruses, the virus particles have

a diameter of 30–35 nm. When viewed in the electron

microscope, the characteristic cup-like depressions of

members of the calicivirus group can be seen on the

surface of the virus particles.

0020 Other Hepatitis Viruses There are other hepatitis

viruses that are not transmitted by the fecal–oral

route. Hence, they are not considered to be associated

with foodborne transmission. The commonest, hepa-

titis B and hepatitis C, are usually transmitted paren-

terally, e.g., by blood transfusions, from injections of

contaminated blood products such as factor VIII, or

from contaminated needles used by drug addicts.

They may also be transmitted by sexual contact.

Other Viruses

Enteroviruses

0021 Enteroviruses form a distinct genus within the Picor-

naviridae family and include the polioviruses, echo-

viruses, and Coxsackie viruses. Most infections are

asymptomatic, but enteroviruses can cause a variety

of symptoms, including paralysis, meningitis, cardio-

myopathy, and less severe conditions such as colds

and fever. Most enteroviruses grow readily in cell

cultures of human and primate origin. An outbreak

of poliomyelitis associated with raw milk in 1914 is

believed to be the first recorded foodborne outbreak

of viral illness. Raw milk was implicated in a further

10 outbreaks in the UK and USA by 1949. Milkborne

outbreaks of poliomyelitis then appeared to cease in

developed countries, even before the introduction of

polio vaccine. This could largely be attributed to the

widespread use of pasteurization. Various entero-

viruses have been isolated from foods such as meat

and shellfish, but there is no clear epidemiological

evidence to suggest that foodborne infection is

occurring.

Tick-borne Encephalitis

0022A further mode of foodborne transmission of viruses

is by zoonotic infection. Cases of tick-borne enceph-

alitis arising from consumption of raw milk from

infected goats, sheep, and cattle or products made

from unpasteurized milk have occurred in Eastern

Europe. The incidence is fortunately rare, owing to

the limited distribution of the appropriate species of

ticks.

Entry of Viruses to the Food Chain

0023Foods may become contaminated with viruses in two

main ways. Food may be contaminated at source,

usually by coming into contact with sewage-polluted

water: this is known as primary contamination. Add-

itionally, food may be contaminated during prepar-

ation and serving by infected food handlers, in just

the same way as some types of foodborne bacterial

contamination can arise. This is known as secondary

contamination.

Contamination at Source

0024Shellfish The most clearly implicated foods in the

transmission of viruses are bivalve molluscs (oysters,

clams, cockles, and mussels). Indeed, most illness

associated with this type of shellfish is viral. These

shellfish are harvested from shallow estuarine and

coastal waters, which are frequently polluted with

sewage. They feed by filtering particulate matter

from the large volumes of water passing over their

gills, and this can include potentially pathogenic

microorganisms. Although human viruses do not rep-

licate in shellfish, they can be concentrated within

molluscs to higher concentrations than occur within

the surrounding water up to 100-fold. Bivalve mol-

luscs are not usually thoroughly cooked before being

eaten, and oysters are frequently consumed raw.

0025Fruit and Vegetables There is the potential for

fruits, vegetables, and salad items to become contam-

inated during irrigation with polluted water and by

fertilization with untreated or inadequately treated

sewage sludge. Many vegetables are cooked before

VIRUSES 6007