The practice of making wine by allowing grape juice to ferment is at least 8,000 years old. The basic process of fermentation is a natural process that occurs readily without any help from humans. Yeast uses oxygen and sugar water to store chemical energy and produce carbon dioxide and alcohol as byproducts. The complexity of winemaking comes into play when you use fermentation to make wine with a specific set of properties. You can demonstrate fermentation by making a drinkable table wine from grape juice and yeast.
Obtain fruit juice without preservatives and enough sugar for fermentation to occur. This combination of factors will eliminate many fruit juices from consideration. For example, citrus fruits generally have more acid than the yeast can tolerate. The best choices include grape juice and apple juice. Make sure the juice is 100 percent pure and doesn't have any preservatives such as benzoate of soda.
Buy yeast. Baker's yeast is readily available at grocery stores and you can also buy wine yeast in stores that sell wine supplies. Both types of yeast are strains of Saccharomyces cerevisiae, a common species in the wild. However, wild species of yeast tend to produce other byproducts besides alcohol that will make the wine undrinkable.
Open the bottle of juice and put a hole through the cap. Add a pinch of yeast to the fruit juice and put the cap back on. Set the bottle aside where it can remain undisturbed at room temperature for about a week.
Replace the cap with one that doesn't have a hole in it and refrigerate the bottle. Crack the bottle open at least once per day to release the excess carbon dioxide. Once the fermentation process is nearly complete, you can keep the bottle sealed to produce a sparkling wine.
Decant the wine into a second container to get rid of the white sediment (dead yeast) and seal this container. Allow the wine to age for at least a month. This wine will continue to mellow for a year.