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

Подождите немного. Документ загружается.

green coffee at a moisture content of 12% w/w is in

equilibrium with ambient air of a relative humidity of

about 65% at 28



C. Deterioration is also markedly

accelerated by temperature, so that it has been stated

that the temperature should not exceed 26



C or even



C. For a shelf-life of 6 months, the air humidity

should also be kept low, and the green coffee at <11%

w/w moisture content. However, there is some evi-

dence that some storage of green coffee is desirable

for flavor quality, with enzymatic generation of favor-

able aroma precursor before roasting. Holding of crop

from one harvesting season to another, i.e., from new

crop to old crop, even under favorable conditions, will

give rise to changes in flavor and also in color (fading

or whitening on long storage), so that the crop year

needs to be known. (See Spoilage: Molds in Spoilage;

Storage Stability: Mechanisms of Degradation.)

Compositional Data: Chemical Changes

During Processing

0018 The fully detailed composition of green coffee, which

is quite complex, has been gradually unraveled by

both classic methods of analysis and the more modern

laboratory techniques, such as high-performance

liquid chromatography. Green coffee, is, of course,

especially characterized by its content of caffeine,

trigonelline, and chlorogenic acids; otherwise, its

composition is similar to that of other comparable

vegetable substances with their protein, carbohy-

drate, vegetable oil, and mineral content. However,

the carbohydrate portion consists mainly of polysac-

charides, the exact nature of which has only recently

been determined. A particular constituent is a man-

nan (of low degree of polymerization), responsible for

the observed physical hardness of green coffee beans.

The two main species of the Coffea genus, described

previously, differ in composition in a number of re-

spects, e.g., caffeine content, on a dry basis: averages

are 12% in arabica and 22% in robusta. Like all

natural substances, variations from an average can be

found, to which can be added those lesser ones ac-

companying green processing and storage effects. It

may be noted, however, that commercial shipments of

green coffee of a particular origin often have a surpris-

ingly uniform composition, resulting from bulking

procedures over the range of producing centers ar-

ranged by marketing authorities in a given country.

(See Caffeine; Carbohydrates: Classification and Prop-

erties; Chromatography: High-performance Liquid

Chromatography.)

0019 Table 1 shows the average composition of the two

main species, in broad terms.

0020 In finer detail, the quantity of free amino acids,

whilst small, may well be of significance as an aroma

precursor in subsequent Maillard reaction during

roasting. The content of free amino acids and that of

reducing sugars may well increase from zero during

green processing through storage; though data are

not available, primarily on account of difficulties in

carrying out the sophisticated types of analysis on site

in producing regions. (See Browning: Nonenzymatic.)

0021There are a number of well-characterized enzymes

present in green coffee, such as the polyphenol

oxidases, which may vary in activity according to

their denaturation, relatable to quality by some

authorities, though discounted by others. (See

Enzymes: Functions and Characteristics.)

0022The distribution of these components within the

bean has been a subject of study, facilitated by scan-

ning and transmission electron microscopy. A distinc-

tion between cell wall polysaccharides and reserve

carbohydrates can be observed, and the occurrence

of a coffee wax at the surface of the bean can be seen.

However, the majority of the lipid material is bound

as a globular membrane between the cell walls and

the cytoplasm.

tbl0001Table 1 Green coffee composition

Ty p i c a l a v e r a g e

content (%, drybasis

)

Component Arabica Robusta

Alkaloids (caffeine) 1.2 2.2

Trigonelline 1.0 0.7

Minerals (as oxide ash; 41% K and 4% P) 4.2 4.4

Acids

Total chlorogenic 6.5 10.0

Aliphatic 1.0 1.0

Quinic 0.4 0.4

Sugars

Sucrose 8.0 4.0

Reducing 0.1 0.4

Arabinogalactan, mannan and glucan

44.0 48.0

Others

1.0 2.0

Lignin

3.0 3.0

Pectins

2.0 2.0

Proteinaceous

Protein 11.0 11.0

Free amino acids 0.5 0.8

Lipids

Coffee oil (triglyceride with

unsaponifiables)

16.0 10.0

Total 100.0 100.0

Also small quantity of volatile organic

compounds

Data updated from Clarke RJ and Macrae R (1987) Coffee: Chemistry, vol.

1; (1987) Technology, vol. 2. Barking: Elsevier, and Clarke RJ (1987) Coffee

technology. In: Herschdoefer SH (ed.) Quality Control in the Food Industry,

vol. 4. London: Academic Press. p. 145.

Data from Bradbury AGW and Halliday DJ (1987) Polysaccharides in

green coffee beans. In: Proceedings of the 12th ASIC Colloquium, pp.265–

269. Paris: ASIC.

Only very limited data available.

1486 COFFEE/Green Coffee

See also: Browning: Nonenzymatic; Caffeine;

Carbohydrates: Classification and Properties;

Chromatography: High-performance Liquid

Chromatography; Drying: Drying Using Natural

Radiation; Enzymes: Functions and Characteristics;

Fats: Classification; Spoilage: Molds in Spoilage;

Storage Stability: Mechanisms of Degradation

Further Reading

Bradbury AGW and Halliday DJ (1987) Polysaccharides in

green coffee beans. In: Proceedings of the 12th ASIC

Colloquium, pp. 265–269. Paris: ASIC.

Clarke RJ (1987) Coffee technology. In: Herschdoefer SH

(ed.) Quality Control in the Food Industry, vol. 4.

London: Academic Press.

Clarke RJ and Macrae R (eds) (1985) Coffee: Chemistry,

vol. 1; (1987) Technology, vol. 2. Barking: Elsevier.

Clarke RJ and Vitzthum OG (2001) Coffee: Recent Devel-

opments. Oxford: Blackwell.

Clifford MN and Willson KC (eds) (1985) Coffee: Botany,

Biochemistry, Production of Beans and Beverage.

London: Chapman and Hall.

Roast and Ground

R J Clarke, Donnington, Chichester, West Sussex, UK

Introduction

0001 Green coffee itself has no comestible value for

humans, and must first be roasted before use as a

flavorful and stimulant aqueous beverage. Further-

more, roasted whole beans must be ground, either

by the housewife or by the manufacturer, after

which brewing in any one of a number of appliances,

manual or automatic, is required.

Roasting Processes

0002 Roasting is a time–temperature-dependent process,

whereby chemical changes are induced by pyrolysis

within the coffee beans, together with marked phys-

ical changes in their internal structure. In particular, a

whole range of different volatile organic compounds

are generated, many of which are responsible for the

flavor/aroma of a prepared coffee beverage, and for

the headspace aroma of the dry product; though it is

still not entirely certain which compounds, either

singly or in combinations, are crucial. The required

changes will take place with a bean temperature from

about 190



C upwards, subsequently needing to be

controlled on account of exothermic reactions occur-

ring, so that bean temperatures up to 240



C may be

reached in a time that should be less than 12 min. The

particular time–temperature chosen will determine

the degree of roast from very light to very dark

(with intermediate subdivisions) assessed in the first

place from visual bean color. The choice of degree of

roast is primarily a matter of consumer preference,

with medium most usual for US and UK tastes.

0003In commercial roasting practice, green coffee beans

under movement are subjected to heat by conduction

from hot metal surfaces, or convection from hot air,

or more generally a mixture of both methods of heat

transfer, together with a contribution by radiation.

Roasters may be broadly classified as in Figure 1.

The modern types of roaster maximize the use of

convective heating, whereas older household ma-

chines will rely mainly on conductive heating. The

most widely used type has been the batch-operated

horizontal rotating drum roaster (with either solid or

perforated walls) in which hot air from a furnace/

burner is passed through the tumbling green coffee

beans. A typical example is shown in Figure 2. De-

pendent upon the air (with combustion gases) flow

rate, the temperature of the hot gases/air has to be

substantially above the bean temperatures to effect

satisfactory heat transfer. In a batch operation, the

roasted beans have to be quickly discharged at the

end of the required roasting period into a cooling car,

or vessel, allowing the upward passage of cold air. In

addition, water may also be sprayed from within the

ROASTERS

Horizontal

rotating drum

Vertical

static drum

with blades

Vertical

rotating

bowl

Fluidized

bed

Pressure

roasting

Perforated

wall

Solid wall

fig0001 Figure 1 Mechanical principles in roasting methods. Reproduced from Coffee: Roast and Ground, Encyclopaedia of Food Science,

Food Technology and Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993, Academic Press.

COFFEE/Roast and Ground 1487

rotating drum, just before the end of the roast, the so-

called water quenching. Not only does this operation

assist necessary cooling, but it also adds a small per-

centage of water by weight to the roasted beans,

which has been found to assist uniformity of particle

size in subsequent grinding. Generated gases, mainly

carbon dioxide, from the pyrolysis often carry solid

particulate matter (chaff), which has to be continu-

ously vented away and, with current environmental

concerns, needs to be ‘after-burned’ before actual

discharge to the outside air. After-burning requires

very high temperatures (450



C), and therefore fur-

ther energy consumption, though lower-temperature

catalytic convertors are also available. In recent

decades, there has been a general movement towards

incorporation of recirculation methods for the hot

gases, in which they are passed back, boosted with

additional air, through the furnace, though with con-

trolled partial release to the atmosphere, still includ-

ing some after-burning or catalytic conversion. A

typically sized roaster of this type would hold

240 kg of green coffee, with an out-turn (charging to

discharging) of 15 min. The furnace/burner will be

either oil- or gas-fired, with a net energy requirement

of about 320 kcal per kilogram green coffee (exclud-

ing after-burning). Recirculation techniques provide

higher velocities of air flow, increasing heat transfer

coefficients, and therefore shortening the roast time

per unit weight of green coffee but do not necessarily

offer energy savings per unit weight of coffee.

0005 The rotating drum principle was first applied to

continuous operation in about 1950 of Jabez Burns

‘Thermalo’ roasters. Since then, roasters based on

other mechanical principles have been developed

and widely used, e.g., the rotating bowl, vertical

drum (with mixing blades) and fluidized air roasters

of various designs.

0006A recent sophisticated type of fluidized bed roaster

is the Nepro Vortex Fluidat Equipment, with three

separately controlled roasting zones and two, cooling

with continuous action, manufactured in Germany by

Nolte GmbH.

0007The general improvement in heat transfer rates has

now enabled shorter roast times (i.e., of the order of

3–5 min) in many of these roasters, with claimed

advantages for the resultant coffee, so-called fast-

roasted coffee of lower bulk density and ‘high yield’

on brewing.

Chemical and Physical Changes Taking

Place on Roasting

0008Green coffee contains sucrose, polysaccharides, and

proteins, together with free amino acids. Consider-

able potential therefore exists for the occurrence of

Maillard-type reactions (essentially between reducing

sugars, derived from partial inversion of sucrose

during roasting, or already present, and amino

acids), leading to the formation of both volatile com-

pounds and high-molecular-weight polymers. Cara-

melization of sucrose also leads to the production of

both volatile and nonvolatile compounds of sensory

significance. Under roasting conditions, reactions are

necessarily complex and difficult to unravel, with the

effect of heat on proteins/carbohydrates in providing

reactive centres and molecules to be also considered.

(See Sucrose: Properties and Determination.)

0009To date, some 800þ different volatile compounds

in roasted coffee have now been identified by modern

gas chromatography–mass spectrometry (GC–MS)

fig0002 Figure 2 Probat batch roaster, type R, showing (1) solid-wall roaster drum, (2) furnace, (3) cooling car, and ancillaries. Courtesy of

Probat-Werke GmbH. Reproduced from Coffee: Roast and Ground, Encyclopaedia of Food Science, Food Technology and Nutrition,

Macrae R, Robinson RK and Sadler MJ (eds), 1993, Kluwer Academic, with permission.

1488 COFFEE/Roast and Ground

techniques by numerous investigators since 1960.

Many of these compounds have also been quantita-

tively determined by GC–MS methods, and their total

amount found to match closely the actual 700–

800 mg per kilogram of roast coffee by steam distilla-

tion or other extractive methods. Some 6000 mg of

semivolatile acids per kilogram, e.g., acetic and

formic acids, are also present. It is clear that amounts

of individual compounds present will be in the milli-

gram or microgram per kilogram range. It has been

reported recently that the volatile complex comprises

by weight 38–45% furan derivatives, 25–30% pyra-

zines, 3–7% pyridines, 3–5% benzenoid aromatics,

1% aliphatics, and 0.5 alicyclics and 1% of various

sulfur compounds (which may well be particularly

important for flavor/aroma) in a medium-roast

arabica coffee. The mode of formation can be dem-

onstrated by model heating experiments of selected

components. Some compounds may also be generated

by straight pyrolysis of single compounds, e.g., trigo-

nelline in forming mainly pyridines, chlorogenic acids

in generating phenols and of coffee oil in forming

small amounts of aldehydes and hydrocarbons. Con-

siderable work has been carried out in recent years on

roast coffee volatile compounds with particular refer-

ence to those that really are significant for coffee

aroma. About 27 are now believed to be important.

(See Chromatography: Gas Chromatography; Flavor

(Flavour)Compounds:StructuresandCharacteristics.)

0010 After roasting, substantial amounts of the com-

pounds present may be found to be unchanged, de-

pendent upon the degree of roast by direct analytical

determinations. However, there is a newly formed

residuum of about 25% by weight of the roast coffee,

which is of uncertain composition but variously

described as melanoidins/humic acids. These are cara-

melized sugars/condensation products of carbo-

hydrates and proteins, linked with breakdown

products of chlorogenic acids or even these acids

themselves. The protein content (assessed by hydroly-

sis into amino acids) holds up quite well, though the

term ‘protein’ is more applicable, similarly, the poly-

saccharide content (assessable by hydrolysis into

sugars), but the coffee oil is practically unaffected,

as is the caffeine. Since there is a loss of mass on

roasting, which will range on a dry basis from some

2–3% for a light roast up to about 12% for a very

dark roast; indeed, the percentage content of coffee

oil and of caffeine will show a slight increase from

green to roasted coffee on a percent dry basis. The

change of chlorogenic acid content (together with

that of its individual component acids) will be marked

on roasting; thus, there is an overall 40% residual

content for a medium roast (with differential figures

for the individual components), which observations

can be used as an analytical measure of degree of

roast. The fate of much of the chlorogenic acids

destroyed during roasting remains obscure. Table 1

shows a typical average final composition for

medium roast coffee. (See Caffeine.)

0011Physical changes in the roasted coffee can be

equally significant, including, of course, color. Scan-

ning electron and light microscopy studies have been

undertaken of cross-sections of coffee beans during

roasting; cell walls are generally intact, but with a

softening of internal structure, and the formation of

cavities/cracking of the surface.

0012There is a marked change in individual bean dens-

ity through swelling during roasting, which will be

reflected in bulk density measurements (both of the

whole roasted beans, and of the roast and ground).

For a medium-roast bean, the void volume percentage

is about 47% compared with virtually zero in the

green bean. The cavities are initially filled with

gaseous products of pyrolysis, mainly carbon dioxide,

which can amount to some 2% by weight of the

roasted bean. On standing, this carbon dioxide

is slowly released and of course, as a result of

subsequent grinding, more rapidly.

tbl0001Table 1 Roast coffee composition

Component

Ty p i c a l a v e r a g e

content (%)

Arabica Robusta

Alkaloids (caffeine) 1.3 2.4

Trigonelline (including roasted byproducts) 1.0 0.7

Minerals (oxide ash) 4.5 4.7

Acids

Residual chlorogenic 2.5 3.8

Quinic 0.8 1.0

Aliphatic 1.6 1.6

Sugars

Sucrose 0.0 0.0

Reducing 0.3 0.3

Polysaccharides (unchanged from green) 33.0 37.0

Lignin

3.0 3.0

Pectins

2.0 2.0

Proteinaceous

‘Protein’ 7.5 7.5

Free amino acids 0.0 0.0

Lipids (coffee oil with unsaponifiables) 17.0 11.0

Caramelized/condensation products

(melanoidins, etc.) by difference

25.5 25.5

Total 100.0 100.0

Also 0.7–0.8% volatile substances

(other than acids)

Dry basis figure for a medium-roast coffee.

Limited data.

Data updated from Clarke RJ and Macrae R (eds) (1987) Coffee:

Te c h n o l o g y , vol. 2. Baking, UK: Elsevier, with permission.

COFFEE/Roast and Ground 1489

Grinding

0013 Grinding of whole roast coffee beans may be con-

ducted either as a small-scale household operation

or on a large scale (e.g., typically of the order of

1000 kg h

1

). For the first, a variety of single-stage

machines, either manually or electrically operated,

have been available for some time. The use of a

rotating serrated disk against a similar static disk

with an adjustable gap is the most usual mechanical

principle adopted. On the larger scale, however,

multistage twin horizontal rollers are employed,

primarily to insure a more uniform particle size dis-

tribution than would otherwise be possible. Up to

four stages may be used, the first two essentially

cracking or crushing the beans into smaller units,

followed by stages for progressively finer grinding.

The type of serrations on the rollers is important;

the most successful type was originated and patented

in 1905 by Lepage and still features in Gump

grinders. The fast roller of each of the first three

pairs has slanting U-shaped corrugations running

lengthways from end to end, whereas the slow rollers

have a straight U-shaped groove, ‘ring-around’ or

helically cut. The gaps are again adjustable. Simpler

corrugations are used in the fourth pair as required

for fine grinding.

0014 Different degrees of grind are defined from the

results of screen or sieve analysis, with three or four

different screens in a set or nest. The nests of screens

need to be shaken/tapped under standardized condi-

tions for a given time (e.g., 5 min for a 100-g sample).

Especially important is the use of standard wire mesh

screens with precisely defined mesh sizes or even cer-

tified screens, as described in BS 410-1976 or later,

ISO 565-1983 and corresponding other national

standards. Relating to roast and ground coffee, the

number of different screen sizes numbered by aper-

ture size within the range of about 1400 mm to

250 mm is quite large, so that it will be noted that

there are a principal and two supplementary series

described in ISO 565, which may result in some

confusion. Care is needed in selection of appropriate

screen sizes to give suitable weight distributions at

each size. In addition, in the USA, there is another

set of sieve sizes in the Tyler series. Plotting the results

of test screenings will show a good straight line rela-

tionship between aperture size (plotted on a linear

scale) and the cumulative percentage weight at that

size (probability scale), except at the ends (Figure 3).

The approximate average size of the particles will be

given at the 50% cumulative weight point. More

sophisticated statistical methods may be employed

to assess average particle size. Newer methods of

sizing by laser beams are becoming available.

0015The grind size required is related to the subsequent

method of brewing to be adopted, and whether for

home use or subsequent large-scale extraction. Grinds

are usually defined as coarse – medium, fine, very fine

– though the screen analysis that determines these

may differ in, say, the UK to the USA. Coarse grinds

were used for household percolators, with an average

particle size of 850 mm (Europe), 1130 mm (USA), and

fine grinds, as used for the now more popular filter

machines, are 430 mm (Europe) and 800 mm (USA).

0016Even finer grinds are required for making Espresso

coffees, around 30 mm average, and optimum condi-

tions have been reported for their brewing.

Packaging

0017Roasted whole coffee beans (RWB) and roasted and

ground (R and G) coffee are not really finished prod-

ucts until they have been packaged for sale to the

consumer. The type of packaging needed depends

upon the time interval between manufacture and

sale/consumption. In the case of small speciality retail

shops, with in-house roasting, simple packets of

1400

1000

710

500

355

250

12562859397

Coarse

Medium

Fine

fig0003Figure 3 Screen analyses for different degrees of grind of roast

and ground coffee, plotting percentage cumulative amount by

weight held at each screen size (aperture in mm) according

to the R.20/3 series of screens (ISO 565 or BS 410). –, coarse;

þ–þ, medium; s–s, fine. Data from tabulation in BS 3999

part 8 (1982). Reproduced from Coffee: Roast and Ground, En-

cyclopaedia of Food Science, Food Technology and Nutrition,

Macrae R, Robinson RK and Sadler MJ (eds), 1993, Kluwer

Academic, with permission.

1490 COFFEE/Roast and Ground

paper or plastic are all that is necessary to maintain

quality, provided the coffee is freshly roasted and

ground and consumed shortly thereafter, say within

a week for R and G coffee (or 10–12 days or longer

for RWB).

0018 However, packaged RWB and especially R and G

coffee from large-scale manufacture have been avail-

able for some considerable time, accelerated by the

advent of supermarkets. There are now twin prob-

lems in the inevitably longer time scale (e.g., 3–12

months or more) between manufacture and consump-

tion. The first problem is that roast coffee, especially

R and G coffee, deteriorates quite rapidly, in respect

of headspace aroma and of flavor, in the presence of

air/oxygen/moisture, and the second problem is that

roasted coffee gradually releases substantial quan-

tities of its entrapped carbon dioxide gas (and other

minor gaseous components), R and G coffee much

more quickly than RWB. In the case of the former,

however, about half will be released in the course of

grinding. The amount of gas still retained plotted

against time is asymptotic in character to zero,

which may well show some 1000 h to near comple-

tion for RWB but substantially less time for R and G

coffee after grinding.

0019 A fully closed package containing freshly ground

roast coffee will therefore rapidly develop a high

internal pressure, maybe sufficient to cause the pack-

age to burst, and is thus dangerous. RWB will cause a

similar or greater problem, though the rate of devel-

opment of internal pressure will be much slower.

0020 In practice, these twin packaging problems have

been solved in a number of ways: firstly, packaging

under vacuum, allowing a low percentage oxygen

content in the headspace to be established within the

package (e.g., 25 mmHg pressure means less than 1%

oxygen headspace level), and also accommodating

release of carbon dioxide, so that the final pressure

in the package may eventually just reach atmospheric;

secondly, by allowing the R and G coffee in bulk to

degas over a sufficient period of time to a low level,

followed by gas purging whilst individual packages

are being filled. In the first method, tin cans have been

used for many years, and more recently plastic pack-

ages, closed by heat sealing and then fitted into card-

board boxes. Such plastic packages have raised a

number of additional problems, not least of seal in-

tegrity due to the hazard of coffee dust, but also due

to a smaller headspace volume than is possible in a tin

can, to take up residual carbon dioxide, and some

prior degassing may be necessary. The package must

not be allowed to become soft, thus restricting the

final internal pressure that is tolerable (around

500 mmHg abs. max.). These packages are so-called

‘hardpacks,’ though in fact a package that has gone

soft does not necessarily indicate per se that the coffee

has deteriorated in quality.

0021In the second method, where no vacuum is

employed, various packaging materials can be used

and heat-sealed, to give so-called ‘soft packs.’ Gas

purging is used to ensure that, again, the residual

percentage oxygen content in the headspace gas is

preferably less than 1%. In both these methods, care

is necessary in the selection of plastic packaging

material (usually laminates) in consideration of gas

ingress/egress, both of oxygen and carbon dioxide

and also of volatile aroma compounds, and, import-

antly, high resistance to water-vapor ingress.

0022A third method that is especially popular in Europe

is in the use of plastic packages to which a nonreturn

valve (e.g., Goglio valve) has been securely attached,

which allows release of excess carbon dioxide when

the internal pressure exceeds a certain predetermined

level. In this way, the amount of prior degassing is

minimized, and the use of a vacuum is not necessary.

0023All of these methods allow a much longer shelf-life

than is possible with simple air packs, though it

should be appreciated that shelf-life is shortened

once any package is opened. Stability is discussed in

the next section.

Deterioration on Storage

0024As will have been evident from the previous section,

both oxygen and moisture are the agents that are

primarily responsible for flavor-quality deterioration

together with the effect of temperature. It should be

noted that like all foodstuffs, deterioration is continu-

ously occurring from the time of harvesting and, in

the case of roasted coffee, from immediately after

roasting. Deterioration of flavor quality is, however,

a subjective phenomenon, though accompanying

chemical changes, only some of which may be directly

related, can of course be detected by laboratory ana-

lytical techniques. Nevertheless, trained panels with

statistical treatment of results can be used to assess

deterioration in terms of rating scales/words. Consid-

erable work has been undertaken at the Munich Tech-

nological University and others in recent years to

study the deterioration of both RWB and R and G

coffee under different conditions. They found it

useful to rate on a scale (10!4!1), with word sub-

divisions of quality as ‘high’ (close to fresh) ‘medium’

(satisfying) and ‘low’ (still acceptable without emer-

gence of stale or off flavours). Table 2 shows some of

these findings. Other data are available for different

conditions but are not directly comparable, showing

the markedly increased rate of deterioration at (1)

higher moisture contents of the R and G coffee

beyond 4%, and (2) percentage oxygen headspace

COFFEE/Roast and Ground 1491

levels beyond 1% (though an air pack is already

included in Table 2). The effect of temperature on

stability has been estimated by saying that each



C decrease doubles the shelf-life and vice versa.

The advantages of storing roast coffee in a refriger-

ator is therefore clearly indicated, provided the

moisture content does not rise, even if the package

has been opened. (See Storage Stability: Parameters

Affecting Storage Stability.)

0025 Various attempts have been made to correlate

flavor quality changes with determinable compos-

itional parameters. It may be noted that the chemical

changes occurring are primarily related to the volatile

organic compounds, called staling; only after a very

considerable storage time do the changes start to

affect the coffee oil by the development of rancidity.

Headspace aroma deterioration may be found to be

more rapid than detectable flavor deterioration, but

does not necessarily mean a corresponding deterior-

ation in the latter.

Domestic and Catering Methods of

Brewing

0026 It has already been stated that roast coffee must be

ground before brewing. There are three further

factors in brewing: coffee-to-water weight ratio, the

appliance used, and the temperatures employed.

Some 14–28% w/w of soluble substances are extract-

able from roasted coffee by hot or boiling water, the

so-called ‘yield,’ though the concentration of these

solubles in the final brew (which will be between

0.75 and 4%, and optimally at 1.2% for US/UK

tastes), most markedly affects the flavor. Brewing is

the extraction not only of soluble substances contrib-

uting only to basic tastes but also of the volatile

substances for overall flavor, which also is not neces-

sarily exhaustive (40–80%). The less polar substances

will tend to reside in the coffee oil within the roast

coffee and will be more difficult to extract than the

more polar substances but are likely to be the more

important for coffee flavor.

0027 Apart from the brewing conditions, the actual

flavor quality will be determined by the choice of

blend used, and the degree of roast. The choice of

grind is also important. Different brewing devices or

appliances (for home and catering use) have been de-

veloped over the centuries, from both the functional

and artistic point of view, leading to a present apothe-

osis in the automatic electric filter machines. The ap-

pliances have been ascribed different names, often

according to the maker, but the mechanical operation

involved essentially is a means of separating the un-

desired so-called spent coffee grounds from the re-

quired brew formed by sufficient contact with water.

The brew should contain as little of the spent ground

particles as possible. At the same time, the brew must

be presented hot (between 50 and 55



C), having been

prepared using water at or somewhat below boiling

temperatures, ostensibly to minimize loss of volatiles

to the air. Two main mechanical principles can be

identified: (1) ‘steeping’ (slurrying) of the R and G

coffee with water, with or without agitation, followed

by sedimentation or filtration or both, and (2) perco-

lation in fixed beds of R and G coffee held in an open or

closed container. In the second method, the water may

be passed through in a single pass under gravity, now

perhaps the most popular, or under pressure (including

steam, as in espresso making), or in multipass, in

which the water may then include increasing amounts

of soluble substances as in so-called household perco-

lators. In the first method, two separate methods can

be identified: infusion and decoction (using boiling

water). Of the components of roasted coffee, only

some will be extracted completely with variable

amounts of the others to reach about 28% w/w total

maximum, and about 21% optimum under household

brewing conditions.

0028Some comparative studies have been carried out on

exactly the same blend/roast degree of coffee in dif-

ferent types of appliance, with one study suggesting a

flavor advantage for an automatic filter machine.

Further Reading

Clarke RJ and Macrae R (eds.) (1987) Coffee: Technology,

vol. 2. Barking, UK: Elsevier.

Clarke RJ and Vitzthum OG (2001) Coffee: Recent

Developments. Oxford: Blackwell Science.

Grosch W (2001) Volatile compounds. In: Clarke RJ and

Vitzthum OG (eds) Coffee: Recent Developments. pp.

68–89 Oxford: Blackwell Science.

Illy A and Viani R (1995) Espresso Coffee – The Chemistry

of Quality. London: Academic Press.

Silwar R, Kampschroer H and Tressl R (1986) Gaschroma-

tische-massenspektrometrische Untersuchungen des

stkaffeearomas. Chemische Mikrobiologie Technolo-

gie Lebensmittel 10: 176.

Vitzthum OG (1999) Thirty years of coffee flavour re-

search. In: Taranishi R, Wick EL and Hornstein I (eds)

Flavour Chemistry – Thirty Years of Progress, pp. 117–

133. New York: Kluwer Academic/Plenum.

Instant

R J Clarke, Donnington, Chichester, West Sussex, UK

Introduction

0001 Instant coffee is the dried soluble portion of roasted

coffee, which can be presented to the consumer in

either powder or granule form for immediate make-

up in hot water, whilst the insoluble parts, or spent

coffee grounds, are left behind at the factory, for the

manufacturer to dispose of. Instant coffee is the name

by which this product is now generally known, though

there are two synonyms, soluble coffee and dried

coffee extract, to express in different ways what the

product is.

Definitions and Composition

0002 Most countries have made a point of insisting that

instant coffee be made from roasted coffee using

water only (which includes steam), though allowance

is needed for the commercial reality of added aroma

oils prepared by mechanical pressing of roasted coffee

or by other nonorganic solvent methods. This view is

expressed in a standard of the International Standards

Organization, ISO 3509–1989 (originated in 1970),

which carries a simple definition, ‘the dried water-

soluble product, obtained exclusively from roasted

coffee by physical methods using water as the only

carrying agent which is not derived from coffee.’ The

European Economic Community (EEC) Directive for

coffee and chicory extracts, 1977 and as amended

1983, in legislative force in all member countries has

a somewhat longer definition, ‘coffee extracts are the

products in any concentration obtained by extraction

from roasted coffee using water only as the medium

of extraction and excluding any process of hydrolysis

involving the addition of an acid or base and,

0003containing the soluble and aromatic constituents

of coffee

0004which may contain insoluble oils derived from

coffee, traces of insoluble substances derived from

coffee, and insoluble substances not derived

from coffee or from the water used for extraction.’

0005Instant coffee is then the dried product of such an

extraction, and can only be labelled as such (or with

synonyms, or foreign language equivalents) when the

product so conforms. Products may of course contain

other soluble beverage constituents, but then need

to be appropriately labelled and all ingredients de-

clared. Some soluble mineral constituents (e.g., 0–

1000 p.p.m. of sodium or calcium ions, etc.) may be

present from the water used in the extraction.

0006Historically, most instant or soluble coffees first

contained added carbohydrates (about 50% w/w)

such as corn syrup solids, since it was found that a

simple aqueous extract of roasted coffee, extracted

under atmospheric conditions (100



C temperature),

could not be dried (usually spray dried) to a satisfac-

tory free-flowing low hygroscopic powder. It was

only from about 1950 that instant coffee at 100%

pure coffee solids became commercially available on

a large scale. This step forward resulted from the

discovery that the desirable carbohydrate (polysac-

charide) substances could be obtained from the roast

coffee itself, by a further aqueous extraction at tem-

peratures up to 175



C and addition to the simple

extract before drying, and thus providing a powder

of satisfactory physical properties. (See Carbohy-

drates: Classification and Properties.)

0007Instant coffees therefore have a higher yield of

soluble substances from the roast coffee than that of

a normal household brew prepared at 100



Cor

below. The additional substances, though extracted

or solubilized at temperatures above 100



C, are fully

soluble in hot or even cold water. It is often asked

what is the difference in composition between cups of

brewed and of instant coffees, when in fact there is a

continuum, since they contain essentially the same

substances, though the proportions or percentages

of individual components will be different according

to solubilization achieved for each. Commercial

yields can differ considerably from one instant prod-

uct to another and, for a short time, were subject to

legislative control in the European Community, but

this was abandoned in 1983. It is now recognized that

COFFEE/Instant 1493

yield is only tenuously related to ‘quality’; the extrac-

tion and retention of aromatic substances in the total

manufacturing process is much more important in

determining flavor quality. The yield (on a dry basis)

of soluble solids from roasted coffee will be around

21% w/w in brewed coffee, up to 32% in exhaustive

extraction at 100



C, and typically 40–55% for

instant coffees, dependent upon blend/roast color of

the originating roasted coffee. A highly water-soluble

substance such as caffeine will be extracted to about

85–100% under household brewing conditions, and

to 100% in instant coffee manufacture, but the actual

percentage content in the soluble solids of the former

will be substantially lower in the latter. In a cup of

coffee, the quantity present will be determined by its

strength, typically from 2 g of instant coffee dissolved

in 150–170 ml of water in a cup. Table 1 shows a

comparison of approximate composition by the main

individual components for a typical filter coffee brew

and a corresponding instant coffee beverage. The

manufacture of instant coffee is accompanied by

some slight hydrolysis of the polysaccharides in

the roast coffee, which is reflected in the slightly

increased reducing sugar content (i.e., arabinose,

mannose, and galactose) and probably assists solubil-

ization of these polysaccharides, not otherwise easily

possible at 100



C. The quantity of volatile organic

substances present in an instant coffee, which are so

important to the flavor of a coffee beverage, will

depend upon the particular process used in its manu-

facture, as described below. The moisture content of

instant coffee is controlled by the drying stage, which

should be less than 5% w/w. (See Caffeine.)

Physical Forms of Instant Coffee

0008In its earlier marketing, instant coffee was almost

entirely sold as a spray-dried powder, light-to-dark

brown in color, free-flowing, and, importantly, with a

bulk free-flow density of between 180 and 220 g l

1

The latter two properties enable easy spooning out

from a container, such that a typical semiheaped tea-

spoon would carry about 2 g of instant coffee to a

150–170-ml cup, giving a strength typically represen-

tative of average UK and US consumer taste

preference.

0009From about 1965 onwards, instant coffee in

granule form became available, though having the

same free flow and bulk density characteristics, but

generally somewhat darker in color than the corres-

ponding powder. With improved retention of aromat-

ics also, such products were compared with brewed

coffee far more favorably by most consumers than

before.

tbl0001 Table 1 Approximate typical composition of brewed and instant coffees

Component

Filter brew

Instant

Roastcoffee

(%, dry basis)

RandGbasis

(%, dry basis)

Extract basis

(%, dry basis)

Per cup

(mg)

RandGbasis

(%, dry basis)

Extract basis

(%, drybasis)

Per cup

(mg)

Caffeine 1.3 1.1

5.3 110 1.3 2.9 58

Trigonelline (including roasted byproducts) 1.0 0.9 4.3 90 1.0 2.2 44

Minerals (as oxide ash) 4.5 4.0

19.0 400 4.2 9.3 186

Acids

Residual

Chlorogenic 2.5 2.5 12.0 250 2.5 5.5 110

Quinic 0.8 0.8 3.8 80 0.8 1.8 36

Aliphatic 1.6 1.6 7.6 160 1.6 3.5 70

Reducing sugars 0.3 0.3 1.4 30 2.2 4.9 98

Polysaccharides (unchanged from green) 31.0 3.2 15.1 320 12.9 28.7 574

Lignin/pectins 5.0

‘Proteins’ 10.0 2.0 9.5 200 5.5 12.2 244

Lipids 17.0 0.01 0.04 1 0.02 0.04 1

Caramelized/condensed compounds

(by difference)

25.0 4.6 22.0 460 13.0 28.9 578

To t a l s 100 21.0 100.0 2100 45.0 100.0 2000

Volatile compounds (excluding acids) 0.08 0.04–0.07 4–7 Variable according to process

Assumed both made from a medium roast arabica coffee.

Brew prepared using 10 g of roasted and ground coffee per cup (150–170 ml) at 21% yield of soluble solids from roasted coffee.

Extract manufactured at a 45% yield of soluble solids from roasted coffee, both on a dry basis; and instant coffee without added coffee oil.

R and G, roasted and ground.

Beverage made up using 2 g of instant coffee per cup (150–170 ml).

Assumed extraction efficiency of 85%.

Assumed extraction efficiency of 90%.

1494 COFFEE/Instant

0010 Whilst freeze drying can produce powders from

liquid feeds, its use for instant coffee was specially

developed to provide a granular product. In a subse-

quent attempt to match the general appearance of

freeze-dried granules, spray-dried powders were

granulated by agglomeration methods (either simul-

taneously with spray drying, or subsequent to it), and

now form a high percentage of instant coffees sold in

the market place. (See Freeze-drying: Structural and

Flavor (Flavour) Changes.)

0011 Dilute or concentrated aqueous extracts of roasted

coffee would also be ‘instant,’ but their stability at

room temperature is poor. Nevertheless, recent

reports show canned coffee liquid to be very popular

in Japan. Frozen granules or chunks (20



C) would

be quite stable, though they have only been

commercialized in a very limited way; spoonable

frozen instant coffee has been developed but requires

the presence of gel-like additives.

Manufacturing Processes

0012The initial stages in manufacture, selection of green

coffees, roasting, and grinding (coarse grind) are as

for roasted coffee. The subsequent basic processes

needed are extraction, drying, and packing, but

with ancillary optional processes of concentration

of extract, separate handling of aromatics and

agglomeration. The know-how and patents are

largely in the hands of large international com-

panies. A typical scheme (simplified) is shown in

Figure 1.

Green beans

Dumper

Cleaner

Rotary

screen

Distributor

Storage

bins

Scale

Cooler

Roaster

Stone

collector

Grinder

Storage

bin

Extractors

Silos

Cooler

Dryer

Blending

tank

Filling

To labeling

and packing

Press cake

for reclamation

Press liquor at 2−7% w/w

S − D − C

solids

Solids at 30/35% w/w

Centrate to

sewage works

Press

Slurry at

86−58%

w/w moisture

Stoner

fig0001 Figure 1 Instant coffee manufacturing process with spent grounds recovery (omitting volatile compound handling). Reproduced

from Clarke RJ and Macrae R (1987), with permission from Kluwer Academic.

COFFEE/Instant 1495