Updated: Feb 28, 2020
When I was in Wales a few years ago, I took a canal boat ride at Llangollen Moorings. The captain of the canal boat was named Patrick, and as he guided the boat along the canal, he was happy to share his opinion about any number of topics, including how to make blackberry gin. It sounded intriguing, so I'm sharing the recipe here.
Take a 1 litre glass jar with a lid. Fill it just past the halfway point with ripe blackberries. Top it off with gin and seal tightly. (Captain Pat recommends using the cheapest gin you can find. He says the more expensive brands “don’t taste right” for this recipe.) Keep in a cool, dark place and shake twice a day. He recommends letting it sit for 8 weeks, but I recommend just one week because you don't want to extract out bitter compounds from the fruit (see my notes below). Strain out the berries. Taste for sugar and add some if you want it to be sweeter.
Use damson plums in place of blackberries.
Use sloe berries in place of blackberries, piercing each one first. Add a few drops of almond extract.
Note: Why the shorter soaking time? According to Andrew Schloss in his book Homemade Liqueurs and Infused Spirits (a book I have reviewed here) infusing liquor with fruit should only take a week, otherwise, the fruit will over-extract and the final product will taste bitter. After a week, the my blackberry gin had turned a lovely rose-violet hue. Mixed with soda water, a slice of lemon, and a sage leaf, it made a harmonious combination that looks great in the glass. The gin itself contains a very subtle flavor of blackberries, but nothing so overwhelming that it could not be used in any cocktail where regular gin would be used. The berries that had been soaked tasted entirely of gin, so they could not be used for anything else.