The brine left in an empty pickle jar carries acid, salt, and spices, so it can replace vinegar in salad dressing, dress potato and bean salads, and serve as the base for quick refrigerator pickles. The same limit that applies to the pickles themselves applies here: do not use the brine if cloudiness comes with a bad smell, mold, or a slippery texture.
Pickle brine is the liquid in which pickles mature; as they mature, it takes on the flavor of the vegetables and spices. In homemade fermented pickles, the brine carries salt and acidity from fermentation; in vinegar pickles, the vinegar provides the acidity. In these 2 cases, the liquid combines acid, salt, and aroma. It is useful in the kitchen wherever all three are wanted together. Its acidity varies from pickle to pickle, so it is hard to predict how much brine to use; adjust the amount by tasting each time. Strain the brine before using it to remove any vegetable scraps and spice seeds.
The most direct use is salad dressing. Add pickle brine to olive oil in place of lemon juice or vinegar, and let it provide the salt in the dressing; in most cases, no additional salt is needed. This dressing works especially well with potato salad, piyaz (Turkish white bean salad), and chickpea and bean salads because boiled potatoes and legumes absorb its tanginess. Add a little mustard to help the brine combine with the oil so the dressing does not separate at the bottom of the bowl. It also gives coleslaw a mellow tang.
Pickle brine can also serve as the base for quick refrigerator pickles. Strain the brine from the jar, add thinly sliced cucumbers, carrots, onions, or cabbage, and put the jar in the refrigerator; as the vegetables sit, they take on the brine’s tang. This is not making a new batch of pickles but using the old brine one more time, and the brine gets a little weaker with each use. Brine that contains garlic and dill will give the new vegetables the same aroma. Keep these pickles refrigerated and eat them soon; pickles meant for long-term storage should be made from scratch according to their own process.
Pickle brine can also go into cooked dishes. Add a little to the sauce of a dish with ground meat or meat in the last few minutes to brighten its rich flavor. It can replace lemon in lentil soup and give the soup a light aroma of spices. Adding a little to meatball mixture gives it a tangy depth. The salt in the brine becomes more concentrated as the dish cooks, so check the seasoning afterward in any dish that contains pickle brine. Brine from hot pepper pickles also carries their heat, so add it sparingly. Do not boil pickle brine for long; adding it in the last few minutes keeps its tang bright.
Use the same criteria for deciding whether to use pickle brine as you would for the pickles themselves. Mild cloudiness from natural fermentation and a thin sediment at the bottom are normal; cloudiness is not expected in vinegar pickles, and sudden cloudiness should be taken more seriously. If cloudiness comes with a sharp, rotten, or ammonia-like smell, a white or colored film on the surface, mold, or slimy vegetables, do not use the brine or taste it. Do not use brine from a jar with a bulging lid or one that makes an unusual hissing sound when opened.