It is very easy to grow grapes, and they take about 3 years to start making fruit. As for fertilizer tastes, that would happen if you use a fertilizer during the time when you are about to pick the grapes. Avoid using fertilizers when you have fruit ready to pick.

Sour flavor, if you do indeed have grapes, could also be because you harvested the grapes too soon. It takes many months for grapes to grow, and then sweeten.

I have lots of grapes, and they currently have big clusters of very green grapes. I won’t even try tasting one until the end of August when they start getting a bit of red color to them.

Some grapes stay green when ripe, but will turn sweet, with time. usually a green grape will turn a pale green, with almost a yellowish color when ripe. Taste one and see.

Some grapes turn red when ripe, others turn purple, some turn black. It varies with the type of grape planted. All grapes turn sweet when ripe. They get so sweet, that if left on the vine, bees and wasps will come to them for the sugar.

Maybe you just harvested too soon.

Where do you live? There is probably a certain month when grapes start maturing. If you are in the USA, most likely, late summer is the earliest for a grape harvest, possibly into October.

The good news is next year, your grape (if it is a grape vine, not a tree of some sort) will have even more grapes.
References :

I don’t think grass fertilizer would affect the taste in a negative way. Where (what state) are you located in? Perhaps it was too wet during the growing season. Maybe that was part of the problem.

Just some thoughts.
References :