Milling wheat – quality criteria and tests - HGCA

Milling wheat –quality criteria and testsWhile almost any wheat canbe milled, millers produce awide range of flours withspecifications tightly defined bybakers for each product.Millers analyse and thensegregate each batch of wheatto meet the quality theircustomers require for eachgrist or blend.Moisture contentWheat quality is threatened when the moisturecontent of stored g r ain exceeds 15%.There is ar isk of infestation and mould as well asmycotoxin formation,all of which can lead torejection.6Specific weightThin,shrivelled grain will not mill to produceadequate amounts of clean,white flour.The specific weight test measures the weight ofgrain – in kilog rammes – that can be packedinto a cylinder of fixed volume,normally 1 litre,and indicates g rain filling.Screenings and admixtureScreenings are undersized g rains and admixtur ecomprises impurities,eg chaf f, weed seeds andearth,which must be removed before millingmarketable flour. Screenings and admixtur erepresent a loss to the miller, so a maximum of2% is normally allo wed.Screenings and admixture are measured usingstandard slotted 3.5 mm and 2 mm sieves.VarietyWheat varieties are categorised by nabimGroups 1 to 4.Groups 1 and 2 are used formost breadmaking g rists while Group 3 is usedfor a range of biscuit,cake and batter flours.Need more information?Protein contentP rotein content is specified for all bake r y f l o u r sand is a key par t of t he contra c t . For mo stb re admaking f l o u r, wheat wi th a prot ein c ont en tab ove 13% dr y matter, i s pre fe r re d . I f pro t e i nc ont ent cannot be ach i e ved using home- grow nw h e a t ,i m p o rted high protein whea t or whea tglute n can be a dded in. For most bis cuits an dc a ke s , gluten fo r mation is not re q u i red andmu ch lower protein f l o u rs may be used .Protein qualityWhen wetted,during dough making,some ofthe proteins in wheat flour form a visco-elasticsubstance – gluten.This can hold gas producedduring fermentation and supports the starchand bran producing a typical well-risen UK loaf.The amount and quality of gluten producedindicates potential performance.No fixedthreshold exists.

Important parametersCharacteristic Farmer test Intake test Buyer responseMoisture content yes yes price deduction or rejectionSpecific weight yes yes price deduction or rejectionScreenings and admixture yes yes price deductionVariety no yes price deduction or rejectionProtein quality no yes price deduction or rejectionProtein content sometimes yes rejectionHagberg Falling Number sometimes yes price deduction or rejectionfor breadmakingMoulds, damaged grain no yes price deduction or rejectionand odoursGrain hardness sometimes yes price deduction or rejectionVisit the nabim website at www.nabim.org.ukHagberg Falling NumberLow Hagberg indicates high enzyme activityand onset of sprouting. A threshold of 250seconds is used for breadmaking wheat andsamples with low Hagberg are rejected.LowHagberg wheat produces bread with a darkcrust colour and a weak,sticky crumb thatcannot be sliced.The Hagberg test is used worldwide.Itmeasures the time,in seconds,a plunger takesto descend through aheated mixture of gr oundgrain and water. The testprovides an indirectestimate of alphaamylaseactivity.Moulds, damaged grainand odoursVisual examination assesses g rain for moulds,Fusarium (pink g rains) and particularly er got.Checks are made for live insects and graindamaged by insects.Experienced staff also assess grain for unusualodours.“Mustiness”or “chemical”odour sindicate stora ge problems.Individual companies set their own criteria forthese assessments.Grain hardnessGrain hardness is a k e y variety trait for milling.Hard and soft wheats have dif ferent processingrequirements and end-uses.The hard wheatsused for breadmaking must absorb suf ficientwater during dough making.Soft wheats arepreferred for biscuits as much added liquid isbaked out to produce a crisp product.By crushing individual g rains within a SingleKernel Characterisation System (SKCS)instrument,the miller can check grain hardnessand identify mixtures of hard and soft varieties.Near infrared calibrations,based on SKCS,canrapidly separate hard and soft wheat samples.7