O-3
Fire loss prevention, self-heating and spontaneous combustion of
hops. Although self-heating and spontaneous combustion of hops has been a
perennial, expensive, disruptive and difficult problem in the hop industry,
little is known about its causes and cures. As a result of three catastrophic
hop warehouse fires in 1999 and 2000, we did extensive investigations on this
problem in 2001. Western Fire Center, Inc. (WFCi) conducted laboratory tests on
the self-heating behavior of Columbus bales (a hop variety with a reputation as
prone to self-heat), Columbus pellets and Nugget bales (a hop variety with a low
tendency to self-heat), using Chen's crossing point temperature (CTP) method. In
this procedure, small quantities of test material are placed in stainless steel
wire mesh cubes equipped with two carefully placed thermocouples, one in the
center and one—the "flank" thermocouple—located 25% of the half-width
from the center. The cube is inserted in a constant temperature oven and the
test proceeds until the center temperature rises above the flank temperature.
From this testing, we predicted the critical radius, critical temperature and
time to thermal runaway for the three materials under assumed warehouse and
ambient conditions. Each of the three materials exhibited thermal runaway under
certain conditions. The Columbus variety was much more susceptible to
self-heating to ignition than Nugget, and Columbus pellets were much more susceptible
than Columbus bales. During harvest 2001, bales of Columbus were produced under
various predetermined kilning and cooling conditions and monitored for
self-heating behavior during storage at constant temperatures of 24, 35 and -2°C.
From this testing we found that: 1) low moisture (<7%) Columbus bales are more
prone to self-heating than high moisture (>11%) bales; 2) Columbus hops kilned
at >66°C are at higher risk of self-heating than hops kilned below that
temperature; 3) improperly kilned and inadequately cooled hops prior to baling
exhibited initial self-heating to potentially quality damaging temperatures and
then cooled; 4) electrical resistance moisture meters are inadequate for hops
with moisture <8%; 5) everything we do to reduce the risk of self-heating also
improves the quality of Columbus bales.
As Vice President, Technical Director for John I. Haas, Inc., in Yakima,
WA, since 1992, David Hysert is responsible for R & D, technical services and
QA. Prior to joining Haas, he enjoyed an 18-year career at Molson Breweries of
Canada where he held various positions in R & D, technical services and QA,
including Vice President, Research and QA from 1985-1992. He received a Ph.D.
from the University of Toronto in bioorganic chemistry in 1971. Dr. Hysert is an
active member of many professional societies including the ASBC, MBAA and
Institute and Guild of Brewing. He was President of the ASBC in 1998-1999.
DAVID W. HYSERT (1), James A. White Jr. (2), Bernard R. Cuzzillo (3), and Scott
W. Garden (1). (1) John I. Haas, Inc., P.O. Box 1441, Yakima WA 98907; (2)
Western Fire Center, Inc., 2204 Parrott Way, Kelso WA 98626; and (3) Berkeley
Engineering and Research, Inc., 2216 Fifth Street, Berkeley CA 94710.