Lesson 2 - Malt Intake, Handling, and Storage
This lesson details the principles and operations of malt intake, handling, and storage. It explains how and why malt is checked on delivery to the brewery. It also covers how it is taken in, processed, and stored, as well as how safety is maintained during malt handling.
Silo Fumigation
Malt can be fumigated to control insect and rodent infestation. The pesticide of choice is often phosphine.
Phosphine gas is produced when aluminium phosphide reacts with water in the atmosphere as shown below.
Phosphine gas is not only toxic, but can also corrode certain metals. Furthermore, it can spontaneously ignite. Commercial products for grain fumigation contain ammonium carbonate to prevent spontaneous ignition by releasing CO2.
Actellic (brand name) is another pesticide that can be used. It has a naphtha (petroleum) base and is used primarily for insect infestation control.
Pesticides are costly, hazardous, and can easily kill people as well as pests. As an industry, we are working to continually reduce the amount of pesticides we use. Pest control must only be undertaken by a licensed pest control professional in accordance with local laws and regulations. Not really a job for a brewer!
These pesticides can be used when a silo is empty or full of grain. If grain is fumigated in the silo, the treated grain may not then be used for brewing within a specified period, sometimes called a withholding period. During this period the concentration of the chemical must drop below its maximum residue limit (MRL) The MRL is the maximum concentration of a residue that is legally permitted (or recognised as acceptable) in or on food. The concentration is expressed in milligrams per kilogram (mg/kg) of the material being treated.
Where an insect infestation has occurred, the grain may need to be sent for cleaning after treatment to remove the dead rodents and insects or grain damaged by the infestation. Damaged grain can lead to a secondary infestation. The silos used for malt fumigation must be purpose-built with sealable loading and unloading ports. The silo will also need a fan to blow air through the grain to remove all the gas after treatment.
The figure below shows a grain fumigation silo:
Figure: Grain fumigation silo