refers to a traditional method of defending harvested hop cones against the effect of fungal foliar diseases, most commonly downy and powdery mildew, and of improving the appearance of hop flowers after harvest. To sulfur hops, sulfur was burned in the oast house to produce sulfur dioxide, a compound that has a long history of controlling microbial growth in food, wine, and beer and of stabilizing product appearance. Dried fruits, especially apricots, still benefit from sulfuring during the drying process. In modern hop production, however, sulfuring hops has been replaced by the use of foliar fungicides. Also, many hop cultivars have been bred to resist plant diseases that were once difficult to control.

Hop sulfuring typically took place during the early hours of drying at a rate of 1 to 4 kg of sulfur burned per 200 to 400 kg of fresh hops. The sulfur was added to the kiln’s fire, with the sulfur dioxide being carried through the hops with the combustion gases during the first 1 to 2 h of drying at a greatly reduced airflow. After sulfuring, the airflow was increased to speed up drying. Sulfured hops could keep for about 1 year. Today, of course, refrigeration allows hops—in hermetically sealed, oxygen-free packaging—to be stored much longer. In the old days, it was essential to sulfur hops as quickly as possible after they were harvested, because moist hop flowers deteriorate extremely quickly, sometimes within just a few hours. The wetter the hop cone, the faster it deteriorates. Yet, sulfuring was often able to restore the appearance, although not the bittering power, of slightly damaged hops. Hop sulfuring is no longer common because sulfur dioxide can react with several flavor-intensive hop resin compounds and thus produce undesirable off-flavors and aromas.