Chaff (/tʃæf/;alsoUK:/tʃɑːf/)[1] is dry, scale-like plant material such as the protectiveseed casings ofcereal grains, the scale-like parts of flowers, or finely choppedstraw. Chaff cannot be digested by humans, but it may befed to livestock,ploughed into soil, or burned.
"Chaff" comes fromMiddle Englishchaf, fromOld Englishceaf, related toOld High Germancheva, "husk".
Ingrasses (includingcereals such asrice,barley,oats, andwheat), the ripe seed is surrounded by thin, dry, scalybracts (calledglumes,lemmas, andpaleas), forming a dryhusk (or hull) around the grain. Once it is removed, it is often referred to as chaff.
In wild cereals and in the primitive domesticatedeinkorn,[2]emmer[3] andspelt[4] 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 calledthreshing beforedrying – traditionally done by milling or pounding, making it finer likeflour. Separating remaining loose chaff from the grain is calledwinnowing – 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.[5]
Domesticated grains such asdurum andcommon wheat have been bred to have chaff that is easily removed. These varieties are known as "free-threshing" or "naked".[6][7][8]
Chaff should not be confused withbran, which is a finer, scaly material that is part of the grain itself.
Chaff is also made by choppingstraw (or sometimes coarsehay) into very short lengths, using a machine called achaff cutter. Like grain chaff, it is used as animal feed and is a way of making coarse fodder more palatable for livestock.[9][10][11]
Coffee chaff is produced from the so calledsilverskin, the thin inner-parchment layer on dried coffee beans, in the process ofcoffee roasting.
Inbotany, chaff refers to the thinreceptacularbracts of many species in the sunflower familyAsteraceae and related families. They are modified scale-likeleaves surrounding singleflorets in the flower-head.[12]
Chaff as a waste product from grain processing leads to ametaphorical use of the term, to refer to something seen as worthless. In theBible, such use is found in Job 13:25,[13] Isaiah 33:11,[14] Psalm 83:13-15,[15] and other places. Chaff also lends its name toa radar countermeasure, composed of small particles dropped from an aircraft.[citation needed]
Hungarian engineer László Schremmer has discovered that the use of chaff-based filters can reduce thearsenic 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 undergroundaquifer.[16]
