isn't this passage only referring to the time of the feast of Unleavened Bread?
So you are to keep the Feast of Unleavened Bread, for on this very day I brought your divisions out of the land of Egypt. You must keep this day as a permanent statute for the generations to come. In the first month you are to eat unleavened bread, from the evening of the fourteenth day until the evening of the twenty-first day. For seven days there must be no leaven found in your houses. If anyone eats something leavened, that person, whether a foreigner or native of the land, must be cut off from the congregation of Israel. You are not to eat anything leavened; eat unleavened bread in all your homes.
(Exodus 12:17-20)
yeast is a living creature. it's found everywhere, on the outer skin of every fruit. an ancient way of making beer or wine was to simply make a mash and set it in a field for a few days -- the wind would blow yeast on it. it's not on the inside of fruit unless the skin is broken so that airborne yeast can find its way in. that's why you have to mash up the fruit when making wine.
honey may be used to feed the yeast, but it's not necessary. all we needed to do to make wine from our blueberries was literally smash them and wait, keeping them in a loosely covered container and stirring the mash daily to minimize the risk of mold growing in it. we progressed to adding some honey and experimented with how long we let it go before straining.
the yeast that's found on the skin of every fruit is no different than the yeast found anywhere else -- the yeast one buys in a store is just a cultivated strain of yeast, whereas what you find in nature may be hundreds of different strains. the advantage of using store-bought yeast is that by cultivating one or two strains is consistency; if one is making thousands of gallons of wine as a business, one can better predict flavor, strength and brewing times. what's found in nature isn't always evenly distributed.