Human beings have been making wine and beer for at least the past 8,000 years. No one knows for certain how the practice started, but it is possible that the first wine was made when squashed grapes became fermented and someone decided to taste the juice (and liked it!). Have you ever noticed the white 'bloom' on the skin of a grape? This is a natural form of a fungus called yeast. So leaving the grape juice around lets the yeast feed on the sugars in the juice and produce alcohol.