Starch is a biological polymer that can be industrially produced in massive amounts in a very pure form. Cereals is the main source for starch production and any improvement of the starch fraction can have a tremendous impact in food and feed applications. Barley ranks number four among cereal crops and barley is a genetically very well characterized. Aiming at producing new starch qualities in the cereal system, we used RNAi and overexpression strategies to produce pure amylose and high-phosphate starch, respectively, using the barley kernel as a polymer factory. By simultaneous silencing of the three genes encoding the starch-branching enzymes SBEI, SBEIIa, and SBEIIb using a triple RNAi chimeric hairpin construct we generated a virtually amylopectin-free barley. The grains of the transgenic lines were shrunken and had a yield of around 80% of the control line. The starch granules were irregular and showed no distinct melting enthalpy and very weak X-ray scattering. Hyperphosphorylated barley starch was achieved by endosperm specific overexpression of the potato glucan water dikinase1 (StGWD1). The content of phosphate esters in this starch was tenfold higher than the control lines. Amylose content was not affected but the starch granules had several pores on the surfaces and a decreased melting enthalpy indicating starch degradation stimulated by phosphate-induced amorphisation. Our work demonstrates the feasibility of starch bioengineering to produce completely novels starch-based polymers implementing two new strategies for in planta starch bioengineering of cereals.