Chaff (; ) is the dry, scaly covering that protects the seeds of cereal grains or similar smooth, dry, scaly plant matter (e.g. such as scaly parts of flowers or finely chopped straw). This glitter is difficult for humans to digest, but some pets can eat it. In agriculture, it is used as animal feed or as waste buried underground or burned.
Etymology
"Chaff" comes from Middle English chaf, from Old English , related to Old High German cheva, "husk".
Grain chaff
In grasses (including cereals such as rice, barley, oats, and wheat), the ripe seed is surrounded by thin, dry, scaly bracts (called glumes, lemmas, and paleas), forming a dry husk (or hull) around the grain. Once it is removed, it is often referred to as chaff.
In wild cereals and in the primitive domesticated einkorn, emmer and spelt wheats, the husks enclose each seed tightly. Before the grain can be used, the husks must be removed.
The process of loosening the chaff from the grain so as to remove it is called "threshing" – traditionally done by milling or pounding. Separating remaining loose chaff from the grain is called "winnowing" – traditionally done by repeatedly tossing the grain up into a light wind, which gradually blows the lighter chaff away. This method typically uses a broad, plate-shaped basket or similar receptacle to hold and collect the winnowed grain as it falls back down.
Domesticated grains such as durum and common wheat have been bred to have chaff that is easily removed. These varieties are known as "free-threshing" or "naked".
Chaff should not be confused with bran, which is a finer, scaly material that is part of the grain itself.
Straw chaff
Chaff is also made by chopping straw (or sometimes coarse hay) into very short lengths, using a machine called a chaff cutter. Like grain chaff, it is used as animal feed, and is a way of turning coarse fodder into a form more palatable to livestock.
Botany
In botany, chaff refers to the thin receptacular bracts of many species in the sunflower family Asteraceae and related families. They are modified scale-like leaves surrounding single florets in the flower-head.
Metaphor
Chaff as a waste product from grain processing leads to a metaphorical use of the term, to refer to something seen as worthless. In the Bible, such use is found in Job 13:25, Isaiah 33:11, Psalm 83:13-15, and other places. Chaff also lends its name to a radar countermeasure, composed of small particles dropped from an aircraft.
Use
Hungarian engineer László Schremmer has discovered that the use of chaff-based filters can reduce the arsenic content of water to 3 microgram/litre. This is especially important in areas where the potable water is provided by filtering the water extracted from an underground aquifer.
See also
Awn (botany) Bran Biomass Combine harvester Rice hulls Rice huller