How did our ancestors make wine?

Chris Smith answered this question...

What an excellent question! So what you're saying is that, these days, when we try to make beverages, then if we're not careful, they end up contaminated and spoiled. The answer is, it's the same when they used to make beer. In fact, people used to drink a lot of beer in Roman times. It wasn't the high strength stuff we have today but because the water was so contaminated, the wine and the beer were better to drink because they were less likely to be contaminated because they had alcohol in them. Basically, if you take grapes and just pick them off the vine and you have relatively good clean starting water, what you're actually relying on is not having sterility in the system because the yeast all comes from the grapes in the first place. If you've ever picked fruit - you might have noticed this, Les - if you look at the surface of a fruit, unless you buy it from a supermarket - what does the surface of a picked plum or some grapes look like if you look at them?

Les - It's got a little bloom to it usually, almost a coating effect, I suppose you could say.

Chris - That's right, and if you were to take some of that coat and then put it under a microscope, what you would see is that that's mainly yeasts. So there are microorganisms there, but there are lots of yeasts in particular naturally on the fruit. If you put those into ideal conditions so the yeast can start to grow, and what the yeast is going to be doing is to consume the sugars in the fruit. If you do it without oxygen being there, it's going to convert the sugar into alcohol and some carbon dioxide. Because there's so much yeast there, pretty quickly it will outcompete the other things that shouldn't be there and it will supress their growth because the alcohol they produce is toxic to the other organisms. The yeast can tolerate it though and so, the yeast outgrows other microorganisms. You end up fermenting the wine and you make a high alcohol or relatively high alcohol beverage where you've used the alcohol actually to supress the harmful microorganisms. This means it's effectively self-sterilising.