Soluble sodium salt is normally used. Greatest activity at pH values below 3. Effective against
a Wide range of micro-organisms. Synergistic with S02. Free acid may precipitate if mixing
inadequate. Allergenic.
More effective than benzoic acid at pH values above 3. Anti-microbial activity increases with
chain length (methyl —> propyl), but solubility
correspondingly decreases. Allergenic.
Normally used as sodium, potassium or
calcium salts. Most effective at low pH values
but retains activity at pH values as high as
6-6.5.’ /Free acid may precipitate if mixing
inadequate. Allergenic, refused GRAS1 status
in the US and only permitted in drinks to be
consumed after dilution in the UK.
Normally used as salt such as sodium
metabisulphite. Most effective at pH values
below 4 and against yeasts, moulds and Gram-negative bacteria. Activity lost by binding
with fruit components to form sulphites.
Produces taint detectable at low
concentrations by some persons. Allergenic.
1 GRAS = generally recognized as safe.
affecting stability by producing creaming, ringing or separation and
must also have no effect on colour, taste or odour.
Brominated vegetable oil was used as an emulsifier system for many years, but while of very good technological performance was with-drawn due to safety fears. Many alternatives have been sought including sucrose esters, such as sucrose diacetate hexa-isobuty-rate, rosin esters, protein clouds, benzoate esters of glycerol and propylene glycol, waxes and gum exudates. None have achieved universal acceptance and unacceptable background flavour is a common problem, especially with rosins and gum exudates. A new product based on modified soy protein may, however, prove satis factory.
Soft drinks
Stabilizers are used both to stabilize emulsions and maintain the
dispersion of fruit solids. Stabilizers also increase viscosity and
improve mouth feel. Alginates, carrageenan, pectins, various gums
including guar and carboxy methyl cellulose are most widely used.
Extract of Quillaia also has stabilizer properties, but is used pri-
marily because of its foaming properties.
Foaming agents
A head of foam is considered desirable in carbonated soft drinks,
such as shandy, ginger beer and colas. The most effective foaming
agents are saponins, extracted either from the bark of Quillaia, or
in the US, Yucca trees.
( c) Carbonation and filling
Carbonation may be considered as the impregnation of a liquid
With CO2 gas. In older plants, some of which are still in use, the
pre-syruping method was employed, in which carbonated water
and sugar syrup were metered separately into the bottle or other
container. This method has been superseded in modern practice by
pre-mix flling in which sugar syrup, Water g, and CO2 gas are
combined in the correct ratio, before transfer to the filler as a
complete beverage. The complete beverage thus’ comes into exis-
tence directly before filling and control of carbonation, and of the
relative proportions of syrup and Water is of critical importance.
Various methods of proportioning are available, but of these the
ratio control system using magnetic flowmeters is easy to clean and
may be combined with a density control system for higher levels of A
accuracy if required. V
The optimum level of carbonation varies according to the flavour
and perceived character of the different drinks. In general terms,
fruit drinks are carbonated to a low level (ca. 1 volume CO2),
colas, ginger beer, alcohol-containing drinks, etc., to a medium
level (2-5 volumes CO2) and mixer drinks such as tonic Water and
ginger ale to a high level (ca. 4.5 volumes), to allow for dilution in
the non-carbonated liquor. Soda water filled into siphons, how-
ever, contains up to 6 volumes of CO2, to maintain internal pres-
sure during use. The use of large (2-3 1) polyethyleneterephthalatfi
(PET) bottles requires a slightly higher level of carbonation
compared with glass to compensate for the‘ loss of CO2 through
the bottle walls during storage and on each successive opening
during consumption.
BOX 3.3 Beyond reasonable doubt
Excessive pressure inside carbonated beverage bottles can make
opening a hazardous procedure. The bottle can contain suffi-
cient pressure energy to propel the cap from the bottle with
sonic velocity, the related phenomena of ‘missiling’ and ‘tailing’,
with risk of severe facial injury. Following a large number of
incidents, a UK local authority, Hampshire County Council,
instituted legal action against a cola bottler under the 1987
Consumer Protection Act. This resulted from an eye injury
suffered by a 15 year old girl, who attempted to remove a
recalcitrant cap with nutcrackers. It was alleged that the head
space in the bottle, which determines the pressure energy and
Which is controlled by the bottler, was excessive at 7% and that
the situation was exacerbated by the design of cap, which was of
insufficient thread depth and of a double sealing design which
delayed gas release. The prosecution was dismissed by the
magistrate following a lengthy and complex technical defence
by the bottler. In the opinion of an expert commentator, the
prosecution should have succeeded and its failure suggests that
the 1987 Consumer Protection Act is failing both to protect the
consumer and to counter powerful vested interests. (W ilhoft, T.
1992. British Food journal, 94 (6), 29-55).
CO2 is a colourless gas of slightly pungent odour which, in part,
forms carbonic acid on dissolving in water.
H20 + CO2 '—> HZCO3
The acid is unstable and has never been isolated, but two series of
salts, the carbonates and the bicarbonates are formed. i
In practice CO2 is the only gas suitable for producing the ‘sparkle’
in soft drinks. The solubility is such as to allow retention in
solution at ambient temperature and yet also allow the release of
an attractive swirl of bubbles from the body of the drink when
slightly agitated. The gas is also inert, non-‘toxic and virtually taste-
less, and is available in liquefied form at moderate cost.
Carbonated soft drinks in a sealed container are in an equilibrium
Condition where gas in the headspace provides the necessary equi-
librium pressure to maintain the remainder of the gas in solution.
The equilibrium pressure varies according to the amount of CO2 in
solution and the liquid temperature. Increase in temperature, or
decrease in pressure, results in a metastable (supersaturated) condi-
tion in which gas is spontaneously released. This phenomenon,
which may be referred to as ‘foaming’ or ‘fobbing’ occurs when a
container is opened and continues during pouring into tumblers
and during consumption. The release of CO2 into the mouth is of
particular importance in providing the ‘hit’ for those drinks
designed to be consumed direct from can or bottle.
The fundamental role of the carbonator is to obtain close contact
between CO2 gas and the liquid being carbonated. Factors deter-
mining the degree of carbonation are:
6.
The pressure in the system;
The temperature of the liquid;
The contact time between the Liquid and CO2;
The area of the interface between the liquid and CO2;
The affinity of the liquid for CO2 (affinity decreases as the
sugar content increases); l
The presence of other gases. u
Pressure, contact time and contact surface are process variables in
all types of carbonator. In many cases carbonators are equipped
With an internal or external cooling facility (carbo-coolers), which
permit the temperature to be controlled. Chilling to 2—6°C avoids
the use of very high pressures during carbonation to high levels
and also has advantages during bottling.
Operation of a carbo-cooler may be described by reference to the
Widely used MojonnierTM system which is of the ‘waterfall’ type.
The system consists of a main vessel containing CO2 at pressures
up to 6 bar. The vessel contains a variable number of heat ex-
change modules through Which a refrigerant is circulated. Incom-
ing product is directed to flow in films down the heat exchange
surfaces. The large surface area of the flm and the tendency to tur-
bulent flow permits effectively simultaneous carbonation and
cooling. Carbo-coolers of this and similar types may, however, b6
unable to obtain the desired level of carbonation under somfi
circumstances. It is then necessary to pre-carbonate the product.
This is normally achieved by injecting CO2 into the pipelinfi
carrying the product to the carbo-cooler.
Carbonated soft drinks are filled into either bottles or cans. Thick-
Walled, reusable, glass bottles were used for many years, but ar€
bging replaced by thin-walled, non-reusable glass and, increasingly,
PET bottles. PET bottles were originally used only for large 2-3 l
Sizes, but are now also used for smaller, individual sizes and thus
also compete with cans. Cans are of the ring-pull type; resealable
Q3115 have been introduced, but found little application.
In recent years filling equipment has achieved a high level of
Sophistication in tenns of throughput and automation and plant
Qflpflblfi of flow rates of 50 000 1/h is not uncommon. Lightweight
cans and PET bottles present problems not encountered with
robust glass bottles, and a number of modifications to filling proce-
dures have been required. A further, and major innovation, has
been the development of ambient temperature filling.
Product refrigeration has been widely used to overcome design
problems in filling machines and to permit maximum output while
maintaining a high standard of fill. Cooling to 5—4°C renders highly
carbonated product quiescent, overcoming such problems as
excess foaming and possible liquid loss. Under conditions of high
humidity, however, cold filling results in condensation on the con-
tainer surfaces and while this is of no importance where absorbent
wooden crates were used for bottles, cans are subject to corrosion.
In later years the use of non-reusable bottles packed in cardboar