What is meant by natural wines is allowing the grapes and juice to ferment by using nothing else, even yeast. This method known as the "old way" relies on the natural (air borne) yeasts to do the fermentation. The air around us carries dozens of types of yeast, some suitable for the production of wine some not. This practice has been around for centuries and even to the present day. Simply because people did not have grape crushers and presses. Some still don't. So you have people standing in a vat stomping grapes, toe jam and fruit flies included. Such wine contains little sterilizer do not age well as they will almost always degrade within less than a year. Slightly sterilized wine will age longer thereby allowing the numerous chemicals, proteins etc in wine to interact and produce aromas and taste.
You may have heard the expression "Last year was a good year". That's because the correct yeast was on the grape skins. Or "last year was not a good year" – just as simple. A stronger yeast called aceto-bacter took over. This yeast produces vinegar. It feeds on alcohol to produce vinegar after the other alcohol producing yeasts have done their work.
Case in point:
Two guys with very Portuguese sounding names come in to buy a bunch of winemaking kits. One says "Dad comes here to get corks and bottle cleaner. he does his wine like in the old country. Don't mention to him that we get out kits here".
"That's ok" I know Albino well!