I have six bottles of sloe gin in the kitchen. Last week two bottles of gin were bought, the store of sugar replenished and a large amount (about three litres by volume) of sloes (prunelles) picked. Luckily, they grow in abundance, surplus even, hereabouts. I use the measure three litres rather than three kilos because that is the most useful measure. However, the berries are round which means there will always be spaces between them so I picked extra, so I would say I had four litres worth. I pick them into a litre wide necked bottle then put them into something else.
The berries need to have stalks removed and be pierced. Do not wash them or cut them. The white bloom on the outside needs to be in with the berries and the sloes should eventually swell. Fill the bottles one third full with sugar, add the gin until the bottle is two thirds full. Shake and allow to settle. Put the sloes in the bottles to fill them. Shake until the mixture is more evenly distributed. The level of the liquer will probably have gone down a centimetre or so, add more sloes. Now shake again and this time the level should be fine.
Regularly shake the bottles until there is no sugar left at the bottom of the bottles. I do it three or four times a day and it reckon with 10 to 14 days before the sugar is entirely gone. The berries will have swollen and the liquer will be a beautiful red by then. Now for the hard bit. Put it away and let it mature for six or more months. I usually make it one year ahead. It is the most wonderful winter warmer and tastes fantastic.
There are purists who will always tell you that the sloes should never be picked before the first frost and indeed I did that a few times in the UK. However, leave the sloes that long in SW France and they will have shriveled up and mostly been eaten by birds. I find the outcome just as satisfying. If it's beer that you want, then try combining a small glass of sloe gin with a half litre of your own home-brewed rye beer before working outdoors on a bitter cold winter day.