plain flour is usually used as it normally wont lump other flours are normally fine though

when the milk is added it has to be cold else it will create lumps

cheese

pepper

mustard

the fat covers the starch from the flour to stop it from lumping when added t the sauce

at 60'c the starch starts absorbing liquid

above 85'c the starch would have absorbed around twice there size in liquid

total gelatinisation happens at 100'c

as it cools down the sauce will become thicker

roux is used as a thickener in a sauce. the roux is cooked to remove the starchy flavor from the flour. When cooking the roux the starch in the flour bursts which thickens the sauce when added

complex carbohydrate

main energy source

potato's

grain.eg wheat corn barley