Optimal distillation results begin with proper extraction and preparation of the material. Ensuring the feedstock is completely free of lipids, and larger molecular weight contaminants such as chlorophyll are paramount, as well as completely decarboxylating and devolatilizing the material prior to first pass distillation.
When troubleshooting, it may be helpful to perform an additional “first pass” to ensure you are completely removing all of the terpenes and lower molecular weight compounds during first-pass distillation, before proceeding to the second pass.
Finally, verify that the system is relatively clean and that the vacuum system is reaching the vacuum depths specified in the SOPs.