Fermented cucumbers are one of the most rewarding things you can make at home. The process is simple — cucumbers, salt brine, time — but the details matter. I use 3.5% brine: 35 grams of non-iodised salt per litre of water.
Pack the cucumbers tightly with dill, garlic, a piece of horseradish, and optionally a grape or oak leaf for tannins that keep them crisp. Pour cold brine until everything is submerged. Three days at room temperature, then somewhere cool. Ready in a week. Best in two.
A white haze in the brine is normal — that's the lactobacilli at work. A little foam on top is also normal. The cucumbers will lose their bright green colour. What you don't want: pink or black mould, or a strongly unpleasant smell.