2009_Book_FoodChemistry

21.1 Coffee and Coffee Substitutes 941
Table 21.2. Composition of green Arabica and Robusta coffee a,b
Constituent Arabica Robusta Components
Soluble carbohydrates 9–12.5 6–11.5
Monosaccharides 0.2–0.5 Fructose, glucose, galactose, arabinose
(traces)
Oligosaccharides 6–9 3–7 Sucrose (>90%), raffinose (0–0.9%),
stachyose (0–0.13%)
Polysaccharides 3–4 Polymers of galactose (55–65%),
mannose (10–20%), arabinose (20–35%),
glucose (0–2%)
Insoluble polysaccharides 46–53 34–44
Hemicelluloses 5–10 3–4 Polymers of galactose (65–75%),
arabinose (25–30%), mannose (0–10%)
Cellulose, β(1–4)mannan 41–43 32–40
Acids and phenols
Volatile acids 0.1
Nonvolatile aliphatic acids 2–2.9 1.3–2.2 Citric acid, malic acid, quinic acid
Chlorogenic acid c 6.7–9.2 7.1–12.1 Mono-, dicaffeoyl- and feruloylquinic
acid
Lignin 1–3
Lipids 15–18 8–12
Wax 0.2–0.3
Oil 7.7–17.7 Main fatty acids: 16:0 and 18:2 (9,12)
N Compounds 11–15
Free amino acids 0.2–0.8 Main amino acids: Glu, Asp, Asp-NH 2
Proteins 8.5–12
Caffeine 0.8–1.4 1.7–4.0 Traces of theobromine and theophylline
Trigonelline 0.6–1.2 0.3–0.9
Minerals 3–5.4
a Values in % of solids.
b Water content of raw coffee: 7–13%.
c Main components: 5-caffeoylquinic acid (chlorogenic acid: Arabica 3.0–5.6%; Robusta 4.4–6.6%).
a greater bean volume increase than conventional
roasting processes. Therefore, the density in the
ground state of coffee roasted by this process is
15–25% lower.
The roasting process is controlled electronically
or by sampling roasted beans. The end-product is
discharged rapidly to cooling sifters or is sprinkled
with water in order to avoid over-roasting or
burning and aroma loss. During roasting, vapors
formed and cell fragments (silverskin particles)
are removed by suction of an exhauster and, in
larger plants, incinerated.
There are different roasting grades desired. In the
USA and Central Europe, beans are roasted to
a light color (200–220 ◦ C, 3–10 min, weight loss
14–17%), and in France, Italy and the Balkan
states, to a dark color (espresso, 230 ◦ C, weight
loss 20%).
21.1.3.2 Storing and Packaging
Roasted coffee is freed of faulty beans either by
hand picking on a sorting board or, at large plants,
automatically by using photo cells. Commercially
available roasted coffee is a blend of 4–8 varieties
which, because of their different characteristics,
are normally roasted separately. Especially strong
blends are usually designated as mocca blends.
While green coffee can be stored for 1–3 years,
roasted coffee, commercially packaged (can,
plastic bags, pouches, bottles), remains fresh for
only 8–10 weeks. The roasting aroma decreases,
while a stale, rancid taste or aroma appears.
Ground coffee packaged in the absence of oxygen
(vacuum packaging) keeps for 6–8 months
but, as soon as the package is opened, this drops
to 1–2 weeks. Little is known of the nature of the