What type of mint are mint leaves from supermarkets

I am assuming your couverture was real chocolate, since you haven't said.

While I don't know the effect of alchohol on chocolate, small quantities of water can easily seize chocolate. It becomes a nasty, pasty, stiff mess.

Typical 80 proof vodka would be 40% alcohol by volume, and so approximately 60% water, so your homemade extract would have had significant water in it.

According to Harold McGee as related in The Kitchn, this sounds like what happened:

The process of refining cocoa beans into chocolate gets rid of all the moisture, and so the final product is actually incredibly dry. Technically, even melted chocolate can be considered a 'dry' ingredient despite its liquid state.

For this reason, adding water to melted chocolate has the same effect as adding water to flour--it turns into a paste. Food science Harold McGee explains that "the small amount of water acts as a kind of glue, wetting the many millions of sugar and cocoa particles just enough to make patches of syrup that stick the particles together..."

You may be able to still use the chocolate for ganache by adding cream, or adding more water so it becomes smooth again, and use it as sauce... but it almost certainly cannot be recovered for covering confections any more.

To prevent this from happening in the future, don't get your couverture wet--from any source.

Note that the flavoring in truffles is normally in the ganache filling, not the couverture; you haven't said you are making truffles, but this gives you a hint:

One way to keep the couverture dry and still have your mint flavor is to add your mint flavoring to the filling.

Another would be to make your homemade mint extract with grain alcohol rather than vodka, so that there is no water in it.

When processing leaves into tea, there are three important steps:

• Withering: this happens in the shadow or in the sun depending on what tea you want to make. In your case, I think sun-drying is proper. The goal is to allow the leaves to dry and soften a bit.
• Rolling: after withering, you can roll the leaves, to squeesh the flavor from the inside to the surface.
• Fixing: after rolling, you need to intensively dry the tea, for example in the oven. This is important to stop the oxidation process and reach a water content level below 5% (otherwise mould will develop later).

So if your tea tastes off, you have to check which step wasn't properly done. Since your tea was musky, it might be that the last step of fixing, wasn't done properly.