The Disposal of Spent Coffee Grounds
From The Soluble Coffee Industry
MARVIN T. BOND. Associate Professor
Engineering Technology
Western Kentucky University
Bowling Green, Kentucky
LARRY W. CANTER, Associate Professor
Department  of CivU  Engineering
Tulane University
New Orleans, Louisiana
INTRODUCTION
Coffee was consumed in Aden, Mecca and Cairo before 1200 A.D. and was
considered an important commodity of world commerce in 1850. However, soluble,
or instant, coffee is a rather recent innocation, made possible by the technological
process improvements that enable the industry to produce a product that meets the
public's acceptance. Soluble coffee first became popular as a result of four years
exposure to the beverage by 15 mUlion servicemen of the United States during World
War II. Since that time the quality of the flavor has continued to improve, and so has
the demand.
The soluble coffee industry has not directed very much effort to the disposal of
its solid waste during these years of expansion. The purpose of this paper is to focus
attention on past endeavors directed toward the development of possible by-products
from the waste and to discuss, in part, research related to composting of spent
grounds as a means of disposal and by-product development.
QUANTITIES OF WASTE PRODUCED
In recent years the producers of soluble coffee in the United States have annually roasted approximately four million bags of green coffee, each weighing 60 kg
(132 lb), solely for the production of soluble coffee (1). Furthermore, there were 80
major instant coffee plants in 1961 that accounted for 98 per cent of the world's production of soluble coffee. Of these plants, the minimal plant used approximately
40,000 bags, or the equivalent of 2,640 tons, of green beans annuaUy (2).
Nearly all green coffee imported into the United States is dried, hulled and
polished in the country of its origin. As the coffee is received it contains 10 to 11
per cent free moisture and is ready for roasting. During roasting the green bean loses
between 14 and 18 per cent of its weight, with an average loss of about 16 per cent.
Of this 16 per cent weight loss, two to five per cent is dry weight loss and the remainder is moisture. After roasting, coffee has approximately two per cent moisture
which is principally bound-moisture. The solid weight loss occurs primarily as a result
of pyrolysis of different components as the temperatures reach 392 to 410 F. In
addition to the weight loss during roasting, the bean increases in size to almost twice
its original volume. Green bean sizes are influenced by environmental conditions as
weU as the species of the plant.  The average length is approximately 9.8 mm, the
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