I had black smelly soft stool, the first part of my stool was regular brown, firm. followed by semi liquid black tar like stool. the night before i'd drunk two glasses of (red) malbec wine.. over there past few weeks my stools have been more light coloure

Possible melena?: If in setting of alcohol, NSAID/aspirin use, etc may be higher likelihood that the described stool was melena, often caused by significant bleeding in upper GI tract, most often from ulcer. This would clearly require MD attention - would need more info, of course. Seek MD esp if re flags e.g. weakness/dizziness, nausea/vomit, fever, weight loss.

You need: to be sure that you are not bleeding! Tarry stools are unlikely to be due to dietary intake including red wines! A visit to your Primary Care Provider is indicated ASAP Hope this helps! Dr Z