Note: Descriptions are shown in the official language in which they were submitted.
~(357S65
This invention reIates to a process and apparatus for
the production of aromatic distillates from roast and ground
coffee, and other aroma bearing substances. More particularly,
the invention is concerned with a process for continuously gener-
ating aromatic distillates by passing steam through a moving bed
of coffee in a counter-current manner under vacuum.
Many methods have been developed for generating aromas
from roast and ground coffee by passing steam therethrough, and
condensing externally the resultant aroma - steam mixture to a
liquid. Occasionally, it has been proposed to fractionate such
mixtures to reduce the amount of water together with the more
undesirable acid components by taking off a 'bottoms' fraction,
and retaining the 'top' fraction containing a higher proportion
of the more desirable coffee aromatics. Such distillates or
fractionates are then added to instant coffee in different ways
or at different stages of the manufacture to obtain more flavor-
ful products than might otherwise be produced without this pre-
process. In particular such distillates may be added to soluble
coffee extracts immediately before freeze-drying.
As, however, the steamed roast and ground coffee has
subsequently to be extracted by hot water to obtain the water
soluble substances for which the well-known system of percolation
column battery is widely-used in practice, it has been found
convenient to carry out this preliminary steaming with the roast
and ground coffee already filled into percolation columns.
Nearly all prior methods for the steaming of roast and ground
coffee for aroma production are based upon an in-column and batch
system of operation. The variables in such methods are steam
pressure applied, and therefore its temperature, the time of
passage of the steam, and the amount of condensate collectedr
expressed conveniently as millilitres per lb. of roast and ground
coffee steamed. The prior art is now replete with such in-column
methods of steaming. - 1 - ~F
~7S65
However, it has been found that the prior methods suffer
in that the conditions necessary for steaming result in the pro-
duction of water-soluble extracts which are degraded, primarily
on account of an excessively high acidity, while the re-addition
of aromatic distillate only partially restores acceptable quality.
When it is considered that steaming conditions may be severe in
respect of time and temperature, and are determined to a large
extent by the pressure of the steam that must be applied to pass
steam through a static and deep bed of coffee in a conventional
percolation column, this degrading effect may not be surprising.
A further objection to an in-column system of steaming roast and
ground coffee is that such a batch system does not lend itself
conveniently to subsequent uniform condensation and fractionation
of the distillate. It has been proposed to discard the roast and
ground coffee after steaming, and add the distillate to the
extract obtalned from fresh unsteamed roast and ground coffee,
but clearly this is an expensive expedient.
Accordingly, it has been further considered to steam
roast and ground coffee under such conditions that the degrading
effect already described is minimized or eliminated. One method
which has been proposed is by contacting the particles o roast
and ground coffee in a separate, moving agitated bed with steam
under pressure. However, this method still proposes the use of
elevated temperatures in the steaming process from which the
degrading effects upon the roast and ground coffee will still be
evident.
It has now been found that good quality aromatic
distillates without impairment of the subsequent water-soluble
extract can be obtained by steaming roast and ground coffee in a
continuous counter-current manner under vacuum conditions, viz.
where the pressure of the steam applied is less than atmospheric,
that is 14.7 lbs. per sq. in.
11057565
In accordance with the present invention, there is pro-
vided a process for the production of volatile aqueous aromatic
distillates, especially from roast and ground coffee, which
comprises passing steam through a moving and agitated bed con-
tained in a closed cylindrical vessel, fitted with a helical
screw conveyor. The steam is passed through the bed counter-
currently to the passage of the roast and ground coffee, with
arrangements for the introduction of the coffee and its exit
from the chamber under vacuum. The resultant water-aroma vapours
are withdrawn under vacuum and subsequently condensed or
fractionated. The steam is introduced at a temperature less than
100C, that is vacuum steam is used.
The precise temperature of the steam at the entrance
and exit, together with the feed rate of roast and ground coffee,
determined in part by the speed of the screw, may be variedj
according to the particular conditions and type of coffee, and
the aroma quality desired. By having the steam temperature
always less than 100C, and having the residence time of the
roast and ground coffee less than about 5 minutes, the degrading
effect, observed on subsequent examination of the water-soluble
extract, with or without the added aromatics, is avoided.
The steamed coffee as it emerges from the continuous
vacuum steaming apparatus is in a reasonably flowable condition,
and may be conveyed with weighing to a fresh column awaiting
filling of a conventional percolation bettery for the extraction
of its water soluble coffee substances in the usual or desired
manner. The grind of roast and ground coffee used should be that
desired in the water extraction.
The aroma-water vapour mixture after condensing in a
suitable manner, as for example, by a condenser with surfaces at
0C or lower, should normally constitute 10 ml or less of liquid
per lb. of roast and ground coffee used. It may be subsequently
added to the aqueous water extract, either dilute as extracted
1057565
or to a concentrated evaporated extract as desired. In all cases,
it is desirable to homogenize the extract with a small quantity
of expressed coffee oil, that is about 0.5~ based on the weight
of soluble solids. Such aroma-enriched extracts may be subse-
quently freeze-dried or processed in other ways as desired to
retain these aromatic volatile substances in a finished powder
or granular product.
The process of the present invention may be carried out
in an apparatus such as that illustrated in the accompanying
drawing. The apparatus comprises a continuous counter-current
contactor consisting of a chamber of cylindrical cross-section,
about 5 feet long and 6 inches diameter. The chamber contains an
open scroll-type helical screw conveyor 2 driven by a motor 3 to
cause movement of roast and ground coffee from one end to the
other; at one end fresh roast and ground coffee is continuously
fed into the chamber through a rotary valve device 4, and the
steamed grounds removed through another rotary valve 5 at the
other end. The feed of roast and ground coffee and the speed of
the screw is adjusted accord ng to the residence time of the
coffee required, which may be about 1 minute or more. A feed rate
of about 300 lbs/hr of coffee would provide a residence time of
about 5 minutes ln substantially full bore flow. Steam is intro-
duced through an opening 6 into the chamber, where the de-
aromatized or steamed coffee is being discharged, and exits at
the other end through another opening 7, and piping 8 connected
to a condenser 9 and fractionater 10 to a vacuum pump 11 maintain-
ing a flow of steam under vacuum, and therefore a temperature of
less than 100C. The pressure differential across the chamber is
monitored by pressure gauges 12 and 13. The flow of steam and
its temperature may be adjusted according to the aromatic quality
and quantity desired in the distillate. For example, some 6 lbs/
hr. distillate may be found desirable, with a vacuum at the steam
exit point of 20 inches.
1~57565
The accompanying drawing illustrates but one embodiment
of the present invention, and is for the purposes of illustration
only. Various changes may be made from the illustrated embodi-
ment although an essential feature of the invention is that the
steam within the contacting vessel should be under vacuum to pro-
vide the particular advantages desired. This vacuum measured at
the exit point for the steam will normally be between 15 inches
and 25 inches of mercury, a higher vacuum may not provide a suf-
ficiently high temperature of the steam to cause rapid wetting of
the coffee, and thus generate the steam aromas required. In
addition, a very high vacuum results in very large volumes of
steam-vapour-aromatics to be condensed, which results in the need
for large heat transfer surfaces. It is also desirable for
optimum quality of aromatic distillate that the roast and ground
coffee used should be freshly ground and the supply pipe directly
connected to the grinding equipment should retain the aromatic
substances generated in the grinding and released in the ground
state.
