Vacuum your leather couch to remove all the loose buildup that could be causing the odor. Often, crumbs and food residue get left behind around cushions and seams, which later turn to odor.
Mix 1 part white vinegar and 2 parts linseed oil in a bowl. The vinegar naturally deodorizes, while the oil restores moisture to the leather.
Dip your cleaning rag into the bowl, and wring it out thoroughly.
Wipe the moist rag over the leather, rubbing in large circular motions until you clean the entire couch.
Wipe off any excess cleaning solution the following day with a clean, dry rag.