Beta-amylase activity. Major cytosolic beta-amylase isoform in rosette leaves and inflorescences stems. Hydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides so as to remove successive maltose units from the non-reducing ends of the chains. Present in the continuous phloem cytoplasm. Detected in phloem sieve elements. Circadian-regulated, with a peak in expression just before the light period in short day conditions. Almost complete loss of beta-amylase activity in rosette leaves and inflorescences (stems). Belongs to the glycosyl hydrolase 14 family.