First let's consider that all wines require yeast for fermenting the grapes. The most common type of yeast used for fermentation is usually made from a mold that grows on grains like wheat, barley, oat, rye and spelt. These grains are considered chametz foods which are actually leavened foods that are prohibited during Passover.
Therefore the Kosher for Passover wines are fermented using the yeast produced from the sugars in the grapes. Also, the wine must not contain common preservatives like potassium sorbate.
Now that we established there is no chametz (or leavened foods) in the wine for Passover, the grapes must be handled by only Sabbath observing Jewish males from the beginning of the 'crush' through the bottling of the wine and there must always be a rabbi supervising the entire process.
Not to confuse you, kosher wine can be made using yeast from grains but it is NOT 'Kosher for Passover'. So it's safe to say that all kosher wine is NOT always kosher for Passover.
There is more than meets the eye when it comes to kosher wine. Today there are many award winning kosher wines produced in many popular wine regions around the world from France to South Africa, Australia, Spain, California, as well as Israel.
There is more than just Manischewitz in every wine shop across the nation.