2009_Book_FoodChemistry

948 21 Coffee, Tea, Cocoa
(21.4)
Table 21.13. Bitter quinic acid lactones in a decaffeinated
coffee drink a
No. Quinic acid lactone Threshold c Concen-
(quinides) b
tration
(mg/l)
I 3-O-Caffeoyl-γ- 13.4 33.15
II 4-O-Caffeoyl-γ- 12.1 19.68
III 4-O-Caffeoyl-muco-γ- 11.2 8.27
IV 5-O-Caffeoyl-muco-γ- 9.7 6.12
V 5-O-Caffeoyl-epi-δ- 60.5 3.28
VI 3-O-Feruloyl-γ- 13.7 6.75
VII 4-O-Feruloyl-γ- 13.7 3.03
VIII 3,4-Dicaffeoyl-γ- 4.9 5.40
IX 4,5-Dicaffeoyl-muco-γ- 4.9 1.65
X 3,5-Dicaffeoyl-epi-δ- 24.9 0.80
a Made by the percolation of coffee powder (54 g) with
water (80 ◦ C, 1.1l).
b The structures of the lactones I, III and V are presented
in Formula 21.4.
c Threshold for the bitter taste.
21.1.4 Coffee Products
The coffee products which will be discussed are
instant coffee, decaffeinated coffee and those
containing additives.
21.1.4.1 Instant Coffee
Instant (soluble) coffee is obtained by the extraction
of roasted coffee. The first technically
sound process was developed by Morgenthaler
in Switzerland in 1938. Ground coffee is batchwise
extracted under pressure in percolator batteries
or continuously in extractors. The water temperature
may be as high as 200 ◦ C while the temperature
of the extract leaving the last extraction
cell is 40–80 ◦ C. The extracts exhibit a concentration
of ca. 15% and are evaporated in vacuum
film evaporators to a solids content of 35–70%.
To minimize aroma losses, the extraction can be
conducted in two stages. In a gentle stage, the first
extract is obtained with a solids content of 25–
27% and carries the main portion of the aroma.
Without concentration, it is mixed with a second
extract which was obtained under stronger conditions
and concentrated. In addition, aroma concentrates
can be isolated by stripping; they can be
added back before or after drying. The technical
extraction yields are 36–46%. Further processing
involves spray or freeze drying. In the latter
method, the liquid extract is foamed and frozen
in a stream of cold air or an inert gas (−40 ◦ C),
then granulated (grain size of 2–3 mm), sifted and
dried in vacuum in the frozen state. Spray-dried
coffee extract can be agglomerated in vibration
fluid beds by steam or spray.
The resultant extract powder is hygroscopic and
unstable. It is packaged in glass jars, vacuum
packed in cans, aluminum foil-lined bags, flexible
polyethylene, laminated pouches or bags, or
packaged in air-tight plastic beakers or mugs, often
under vacuum or under an inert gas.
Like roasted coffee, instant coffee is marketed
in different varieties, e. g., regular roasted or as
a dark, strongly-roasted espresso, or caffeine free.
Instant coffee contains 1.0–6.0% moisture. The
dry matter consists of 7.6–14.6% minerals, 3.2–