The production of polyethylene terephthalate (PET) bottles can lead to the formation of acetaldehyde. Because acetaldehyde has a significant influence on the taste of the contents, it is important, when manufacturing bottles of PET, that the plasticising process should proceed very gently. The decisive factor here is the stress to which the material is subjected, because a local increase in temperature encourages the formation of acetaldehyde. A suitable design of the screw geometry can ensure gentle plasticising and, by dispensing with AA blockers, can lower material costs.