Studi peningkatan mutu minyak sereh wangi (cymbopogon winterianus) dan minyak nilam (pogostemon cablin) menggunakan metode distilasi uap dan kolom fraksionasi = Study on the quality improvement of citronella (cymbopogon winterianus) and patchouli (pogostemon cablin) oil using steam distillation method and fractionating column