Combine the vinegar, salt and sugar in a small non-reactive saucepan (such as stainless steel, glass, ceramic or teflon) over high heat. Whisk until the salt and sugar are dissolved. Transfer the liquid into a bowl and whisk in the cold water. Refrigerate brine until ready to use.

Stuff the cucumbers into two clean 1-quart jars. Add the coriander seeds, garlic cloves, mustard seeds, red pepper flakes, dill sprigs, and chilled brine into jars, dividing evenly. If necessary, add a bit of cold water to the jars until the brine covers the cucumbers. Cover and refrigerate about 24 hours, then serve. The pickles will keep in the refrigerator for up to one month.