ROASTING AND GLAZING.
Coffee undergoes essential chemical changes in the process of roasting.
In the raw or natural state the coffee-bean is tough and horny in
structure and entirely devoid of the appearance, character and peculiar
aroma that so distinguishes it in the roasted condition, and by which
it is best known to the public. The testa or investing membrane of the
raw bean has a layer of long cells with a peculiar pitted structure,
containing a crystaline substance chemically termed _Caffeine_, and
another known as _Caffeic_, or tannic acid, while the inner substance
consists of an assemblage of vesicles of an angular form, the cavities
of which include in the form of little drops a considerable quantity of
a highly aromatic oil technically termed _Caffeone_, on the presence
and amount of which the fragrance and active principles of the coffee
depends, and by which its commercial value in the roasted state is
estimated. The existence of this “coffee oil” makes itself known in
a striking manner by roasting; being driven out of the beans by the
intense heat, it is partially volatilized and, together with other
products of the roasting, produces the characteristic aroma peculiar
to roasted coffee, an odor possessed by no other known substance. In
the operation of roasting the beans swell up and open at the furrow
by the liberation of the gases within their substance, their weight
decreasing, but volume increasing in proportion to the extent to which
the operation is carried, developing the aromatic oil and liberating
at the same time a portion of the caffeine from its combination with
the caffeic or tannic acid. The amount of this aromatic oil contained
in coffee varies from 8 to 13 per cent. at least, one-half of which is
lost by evaporation during the roasting process, so that it may prove
a paying experiment to attempt to collect it, especially in large
establishments where large quantities of coffee are roasted and several
pounds of this valuable oil are dissipated daily, which would no doubt
find a ready market at a good profit for the making of liqueurs, or
medicinal use.
Before being roasted coffee also contains from 6 to 8 per cent. of
sugar, which after roasting is reduced to as low as 1 per cent. and
sometimes even to zero, from which it would appear that the description
of sugar (cane) present in the raw coffee suffers destruction during
roasting, which, however, is not the case, as in the process of
roasting the saccharine matter in the raw bean is converted into
caramel. A change in the fat of the raw coffee is also brought about by
the roasting, for where ether extracts only some four to five parts of
fat from the raw coffee beans, it readily extracts double that quantity
from the roasted beans. So striking is this fact that Von Bibra has
even credited the roasting process with the production of fat, whereas
the action is only mechanical in bursting the fat-cells of the raw
bean, thereby rendering the fat accessible to the solvent action of the
ether.
The operation of roasting also tends to make coffee soluble in boiling
water, as when raw coffee is perfectly exhausted by means of boiling
water, it yields up only 25 per cent. which passes into solution, while
roasted coffee, on the other hand, when completely exhausted by means
of boiling water yields readily upwards of 40 per cent. of soluble
matter, proving that in actually using coffee as a beverage, we are not
in the habit of making anything like a complete extraction, as only
some 10 to 12 per cent. of the active principles of the coffee passes
into the liquid.
The modern appliances for the roasting of coffee are numerous and
labor-saving to a great extent, many of them are, however, calculated
only to enhance the appearance of the bean, while others enable the
roaster to obtain almost to perfection the full development of the
aromatic properties of the coffee. Coffee is roasted for commercial
purposes and domestic use in a large sheet-steel or malleable-iron
cylinder mounted on a hollow axle, so as to revolve over a brisk fire
and allow the gases generated during the torrefaction to escape. The
surface of the cylinder is perforated with a number of small holes
for the purpose of allowing the vapor arising from the coffee in the
process of roasting to pass off readily, and through the interior runs
laterally four ridges, the object of which is to toss it about in all
directions, causing it to pass from end to end, and diffuse a uniform
heat to every part of the coffee in order to make the “roast” even
and regular in appearance. This cylinder is again encased in a frame
brick-work at the bottom of which is built a coal fire well distributed
so as to heat all portions of the cylinder at the same time during
the operation. On the outer head it has a small opening through which
the operator occasionally inserts a “tryer” to enable him to note the
progress made as the process advances, the cylinder being also so
arranged that it can be drawn from over the fire when it is required to
either fill or empty it through a slide or hopper in the centre. It is
operated by steam-power, revolving slowly but regularly, and having a
capacity of from 25 to 300 pounds.
After roasting, the coffee is run off into a large wire-bottomed box
termed a “cooler,” to the end of which is fitted a powerful fan or
“blower” used for forcing cold air through the hot beans and preventing
the volatile oil from exuding, the coffee being thoroughly agitated
during the process, the hulls, chaff and stems being removed meantime
to a large extent by the fan and sieve. Thirty-five to forty-five
minutes is usually the time consumed in the operation, the former
for a “Light” and the latter for a high or “Dark” roast, the entire
process of roasting, cooling and rebagging occupying about one hour.
In roasting, coffee loses in weight from 12 to 16 per cent., according
to the age and nature of the coffee under treatment and the extent
to which the operation is carried, the average, however, being 14
per cent. for old and well-seasoned coffee, which accounts for the
relatively higher price--three to six cents per pound--of roasted
coffees, according to the price green and the loss per cent. in
roasting. But, it at the same time increases in bulk--100 volumes of
raw coffee yielding from 150 to 160 volumes of roasted--that is, two
pints of raw beans will yield three pints roasted. It also loses from
1 to 2 per cent. more in the warm months of summer than in the damp
months of winter, for which reason it should not be roasted as high
in the former season as in the latter, owing to its greater tendency
to sweat and absorb the higher temperature, thus causing the volatile
oil to exude, and dissipate and impart an astringent taste to the
infusion. When coffee is roasted light-brown, or until it assumes a
pale-chestnut color, the loss is from 13 to 14 per cent. the quantity
of extract obtained from such roast by means of boiling water ranging
from 20 to 21 per cent. of the weight, while the loss in weight of the
extract will be much larger if the roasting process is continued until
the color becomes dark-brown or black by over-roasting. New, moist
and light coffees lose a larger percentage than old, dry and solid
ones, the average being about 14 per cent. The operation of roasting
coffee is one of the greatest exactness, amounting almost to an art,
perfect roasting requiring not alone skill and judgment but experience
and constant practice, as not only the style, strength and flavor but
also the commercial value of the coffee depends upon the operator
deciding when it is properly parched or roasted. It is also one of a
crucial nature, for equally by insufficient as well as by excessive
roasting, much of the aroma of the infusion is lost, the beverage under
either of these circumstances being neither agreeable to the palate or
exhilarating in its influence. The operator, for these reasons, must
judge of the exact amount of heat required for the adequate roasting of
the different varieties, which, while variable, the range of roasting
temperature proper for roasting the various grades is only very narrow.
In a modern, well-equipped coffee-roasting establishment, the coffee is
handled almost exclusively by machinery, being fed into the cylinder
from hoppers, emptied into the cooler from the cylinder and from thence
into the bins by drafts of air through tubes or pocket-elevators, so
that the coffee is scarcely once handled during the entire process.
The entire art of coffee roasting may be summed up in the following
sequence: (1) Starting the machinery in motion. (2) Starting a brisk
fire with enough coal for a single roast. (3) Putting in the coffee
before the cylinder becomes too hot. (4) Opening the draft and keeping
up a brisk fire during what is termed the steaming period. (5) When the
beans begin to crackle and the steam changes into an aromatic vapor,
rake the fire well, put on sufficient coal to make the next roast and
shut off the draft. (6) Empty the coffee from the cylinder into the
cooler and cool off rapidly, then sift and pack. If a light color is
required roast quickly, if a dark, slowly. The exact time for a perfect
roast under these rules depend to a great extent on the size of the
cylinder, the quantity of coffee to be roasted, the amount of heat
and the color desired, the average ranging from 30 to 40 minutes. The
addition of a little water to the coffee when it begins to crackle in
the cylinder, will cause the beans to swell up, liberate the chaff and
make the process safer by extinguishing any sparks that may by accident
occur in the cylinder. It also preserves the aroma longer to some
extent when used in moderation, but will not, as is sometimes claimed,
protect it from atmospheric influences, but on the contrary makes it
more liable to such influences, particularly when used in excess.
When the beans begin to crackle the revolutions of the cylinder are
increased for a short time in order to prevent them from scorching or
burning, a bluish vapor is emitted at the same time, which indicates
that the coffee is nearly if not quite roasted. At this stage the
operator pours on the coffee a quantity of water to prevent it from
burning, the rapid evaporation from which reduces the intense heat and
causes the beans to burst open and swell up to about double in size.
The use of a little lard at this juncture will impart to the beans a
smoother, glossier and more attractive appearance. The addition of
water in the roasting of coffee is not, as is generally supposed,
intended to increase its weight--unless when used to excess--as the
intense heat converts it into steam which rapidly passes off in the
air, many old roasters contending that coffee cannot be properly
roasted without the use of some water. In the proper roasting of
coffee a strong, well-distributed heat extending the entire length of
the cylinder is imperative. The cylinder should never be allowed to lie
empty over the fire for any length of time or become too hot before
the coffee is put in, as the beans will become mottled or “specked” if
poured in while in that condition, thus detracting from the appearance
and value of the roasted coffee.
An experienced roaster can readily discern when the coffee is properly
roasted, by the light bluish vapor arising from the coffee, as well
as by the smell of the aromatic principle developed as it evaporates
from the cylinder at this stage of the operation, without even once
examining it during the process. A perfect “light roast” should be
free from specks and other blemishes, of a cinnamon-brown color,
even, uniform and oily in appearance, much depending on the amount of
this latter property developed in the process, imparting as it does
a pleasanter and more agreeable aroma as the quantity is increased,
making the liquor blander and more mellow in the cup. While a perfect
high or “dark roast” when required should be of a deep chestnut or
chocolate-brown color, oily and free from all burnt or scorched beans,
as the latter, no matter how few the number, invariably spoil the
flavor of the coffee in the infusion, irrespective of its fineness or
value. Over-roasting dissipates the active principle (Caffeine) to
which the coffee owes its refreshing and stimulating properties while
under-roasting imparts to the infusion a raw, uncooked, grassy or
astringent flavor by not properly developing it. So that the finest
grades of coffee when imperfectly roasted--that is, be under or
overdone--yield an inferior liquor to the poorer grades when properly
roasted. As stated before, coffee contains a crystaline substance
termed caffeine (identical with the theine of tea), which is volatile
in its nature, and every care must be taken to retain this principle
in the coffee, for which reason the beans should be roasted only until
they are of a pale-brown color; again, if they are roasted too dark
this essential property is destroyed.
The proper cooling of coffee after roasting is also an operation of
great importance. If the coffee has been properly roasted and the
beans well developed, it must be cooled quickly to prevent them from
becoming too dark-colored or mottled in appearance. When the coffee has
been cooled and cleaned it is then packed, the operations of roasting,
cooling and rebagging occupying altogether about one hour.
In France and other European countries it is the custom to roast
coffee in small quantities, so that the whole “charge” is well under
the control of the operator during the process, while in this country
large roasts are the rule, in dealing with which much difficulty is
experienced in producing uniform torrefaction as well as in stopping
the process at the proper moment. A novel method for roasting coffee
in use in France is to put it in an iron globe, suspended over a brisk
fire, and containing a tubular shaft perforated with holes smaller than
the beans, through which passes the vapor generated from the coffee in
the process of roasting and issuing out of either end of the shaft or
axis of the globe. As these openings are small, but a limited amount
of the vapor escapes, thus confining the aroma within the globe and
securing the retention of the volatile or essential element of the
coffee to a greater degree than is possible by the cylindrical method
of roasting. When the globe is filled and suspended over the fire
an iron cap is placed over it so as to completely surround it, but
leaving an intervening space between it of about three inches, the
object of which is to secure the full power of the heat, which being so
confined circulates completely around the globe, the retention of the
vapor under this high pressure preserving to a still greater degree the
aroma of the coffee. The application of the heat by this method is very
uniform, while the motion of the globe distributes the beans equally
about the interior and thus removes any possible chance of scorching.
The roasting process also usually develops in many coffees more or
less whitish beans, technically termed “quakers” but more properly
“blights,” being in reality blighted or immature beans, which, having
ripened to an extent on the tree and after obtaining a certain growth
cease to draw further nutriment from it, thus failing to develop into
healthy fruit. These peculiar beans detract considerably from the
value of the coffee, and cannot always be detected in the natural
state except by experts and others accustomed to the constant handling
of raw coffee, but in the roasted condition their real character is
unmistakably shown, presenting as they do a yellowish-white color,
totally devoid of the moisture, oil and flavor so characteristic of the
healthy bean. They exist to a much greater extent in some varieties
more than others, most notably in lowland and coast-grown coffees--in
mild grades more than strong--the only kinds most unaffected being
mountain-grown and “washed” coffees, the blighted beans in the latter
rising to the surface in the process of washing and carried off by the
water. Some authorities contend that these “blights” or “quakers” in
coffee instead of being, as might be naturally expected, detrimental
or injurious to its drinking qualities really improve it by softening
or mellowing what may otherwise prove to be a harsh or astringent
flavor, thereby rendering it smoother and more palatable. Such a claim
is simply preposterous, as the said beans are entirely devoid of any
of the properties distinguishing coffee, possessing neither caffeine
or caffeone, the two principal constituents of coffee, and an infusion
prepared exclusively of “quakers” will be found to resemble more
closely, in flavor and aroma, a decoction made from roasted peanuts
than anything else it may be likened to.
Raw coffees are distinguished in commerce by the names of the
countries, districts, localities, plantations in which they are grown
or from the ports of export, and it is found that the produce of each
particular country and respective district maintains a fairly constant
and distinctive flavor and character of its own. While in the roasted
state this distinctive character disappears, the process of roasting
largely destroying these distinguishing features of raw or green
coffee, making it very difficult for any but experts to determine from
its appearance when once roasted its kind or origin. After coffee has
been once roasted it should be kept in air-tight bins and sold or used
as fresh-roasted as possible, as after the process the aroma constantly
escapes, thereby losing its strength and fragrance rapidly on exposure
to the oxydizing influences of the atmosphere. Neither should it be
exposed in damp or humid weather, as it constantly absorbs moisture
which makes it tough and difficult to grind, or placed in the vicinity
of any foul or foreign odors, the porous and sensitive nature of the
roasted bean making it liable to absorb such flavors, for which reason
wooden and freshly-painted bins should never be used to hold roasted
coffee, as it readily absorbs the wood and paint flavors, which become
very pronounced in the infusion.
GLAZING.
It has been the custom for some years back to coat or glaze coffee
with certain gluey or starchy compounds, ostensibly to protect the
beans from the oxydizing influences of the atmosphere, preserve the
aroma and clarify the liquor in preparation, each roaster and dealer
having a different compound for the purpose. It is most generally
composed of various glues, moss and other starchy substances and is
usually prepared by placing the materials composing the compound in a
cask, vat or tank filled with boiling water conveyed through pipes or
by injecting steam, thoroughly stirring it at the same time until it
is mixed to the requisite consistency. After the solution is prepared
it is applied to the coffee while hot, generally in the cylinder
while revolving, which diffuses the material and imparts an even and
uniform coating to the coffee, adhering and hardening as it cools.
But the claims made by roasters and others who coat or glaze coffee,
that large quantities of eggs are used exclusively in the preparation
of the glazing compound is simply absurd, as is also the claim that
it is resorted to for the purpose of closing the pores, to protect
and retain the aroma and for self-settling purposes. The real object
being to conceal defects, disguise low grades and damaged coffees,
as well as to add weight and color to light, chaffy and “quakery”
coffees, the process adding all the way from 5 to 10 per cent. to the
weight, according to the nature of the coffee and the character of
the substance used; light, chaffy-bean coffees absorbing more of the
material than the hard and solid ones, while the softer and rougher the
bean the more it improves in appearance by the process.
What is known as the “Egg-glaze” is prepared from eggs alone, mashed
and applied after the coffee has been first cooled, and then baked
on by means of a hot blast, when it forms a hard, transparent shell,
protecting the coffee until it is ground and ready for use; and also
serving to clarify the liquor in the pot after infusion. Another
composed of one part gum arabic dissolved in water, to which is
added four parts starch, with sufficient water to make it limped,
the whole being boiled for upwards of twenty minutes, and which is
best accomplished by inserting a small pipe of live steam from the
boiler into the compound until it is reduced to the consistency of
cream; then, after stirring well, it is poured on the coffee while
in the cylinder as it revolves, or it may be spread over it while in
the cooler, if proper care be taken to diffuse it well. Still another
excellent compound for glazing coffee is prepared from one part Irish
moss, one part gelatine, one part isinglass, one ounce sugar and two
dozen eggs, the first three ingredients being first boiled in water,
then strained and applied as in foregoing formula. For the purpose of
imparting a lustrous aspect to roasted coffee, a liquid has recently
been invented, the composition of which is so far unknown. It has a
specific gravity of 0.868 at 15 degrees, burning with a sooty flame and
leaving no fixed residue. It absorbs no iodine when treated, and is but
little affected by chromic acid or concentrated sulphuric acid, taking
only a slight color when treated with the latter. It is clear and oily
in appearance, but entirely free from color, taste, or smell, and mixes
in all proportions with petroleum, from which fact it would appear to
be nothing more than a highly purified petroleum oil, in which case it
must be classed among the illegitimate additions to roasted coffee.
GRINDING.
The process of grinding the roasted bean is also one that requires
more attention than is generally bestowed on it. Coarse-ground coffees
require protracted boiling in order to extract its full strength, and
too much boiling is fatal to the production of good coffee in the cup.
But, on the other hand, it may be ground too fine, so that just to what
degree of fineness it should be ground depends in a great measure on
the method of preparing it for use.