This method describes how to determine whether kernels in a lot of barley are cracked by means of the iodine-starch reaction.
Barley intended for the production of malt is to be evaluated on the basis of the characteristics described below.
Detection of cracked kernels is based upon the reaction of iodine with starch. Unprotected starch grains located in the cracks are dyed with iodine, thereby producing a vivid shade of blue, making the cracks easily discernible.
Malt intended for use in beer brewing or elsewhere in the food industry
The substrate for the limit dextrins is prepared by adding excess β-amylase to a standard solution of starch. An extract of malt is added, and the α-amylase present in the malt brings about the degradation of the limit dextrins. With the addition of an iodine solution, the time required for the standard color of the starch-iodine complex to be reached is known as a “dextrinizing unit” [1].
Applicable for all (laboratory) worts
The Congress wort is heated in order to inactivate the amylolytic enzymes, and afterwards, yeast is added and the wort is allowed to completely ferment out at a minimum temperature of 20 °C in a fermentation tube (fig. 1). The difference in the extract before and after fermentation is measured in order to calculate the limit of attenuation.
Applicable for all (laboratory) wort
The Congress wort is heated in order to inactivate the amylolytic enzymes, and afterwards added to an Erlenmeyer flask along with 7.5 g/100 ml yeast where it is allowed to completely ferment out under constant agitation. The difference in the extract before and after fermentation is measured in order to calculate the limit of attenuation.
Applicable for all (laboratory) worts
The Congress wort is heated in order to inactivate the amylolytic enzymes. Afterwards, 16 g/100 ml yeast is added, and the wort is allowed to completely ferment out in approx. 7 h.
wort, beer
Yeast (16 g/100 ml) is added to (boiled) wort or beer in an Erlenmeyer flask and allowed to ferment completely in approx. 7 h under constant agitation. The limit of attenuation is calculated from the difference between the extract content prior to (original gravity) and after fermentation. [1, 2, 3]