Monoterpene synthase (mono-TPS) involved in the biosynthesis of monoterpenes natural products, constituent of coffee beverage aroma (PubMed:23398891). Catalyzes the conversion of (2E)-geranyl diphosphate (GPP) into limonene, beta-pinene, sabinene and beta-myrcene, and, as minor products, alpha-pinene and alpha-terpinolene (PubMed:23398891). Can also, with a low efficiency, use farnesyl pyrophosphate (FPP) as substrate to produce beta-farnesene (PubMed:23398891). Not able to use geranylgeranyl pyrophosphate (GGPP) as substrate (PubMed:23398891). (2E,6E)-farnesyl diphosphate = (E)-beta-farnesene + diphosphate (2E)-geranyl diphosphate = diphosphate + limonene (2E)-geranyl diphosphate = beta-pinene + diphosphate (2E)-geranyl diphosphate = diphosphate + sabinene (2E)-geranyl diphosphate = beta-myrcene + diphosphate (2E)-geranyl diphosphate = alpha-pinene + diphosphate (2E)-geranyl diphosphate = diphosphate + terpinolene Binds 3 Mg(2+) or Mn(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Monomer. Confined to fruits. Observed during fruits development 25 weeks after pollination. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family. Tpsb subfamily. Truncated N-terminus.