I've heard that some Chinese Master stocks are 100 years old. If so, how did they store their master stock before the refrigerator was invented?
The thing here is to use the stock often. Add to it often with other juices. Keep it at or above 160f. Filter often to keep impurities out. At 160f bacteria does not form in it. If let set bring to boil. Skim & filter. The cook stoves or heat never shut off. If stoves ovens cooled to fast they could crack. So were always kept warm. Then came refrigeration. Modern ovens & stoves. Brick & stone stoves are like that. It takes 3 days to bank down the heat before you can cool them or they crack or fall apart. Fire clay. Turn of the heat cool fast. The clay will turn to powder. So to use the banked down heat. overnight sauces could be kept warm. Meat slow cooked in them at night. To use that heat.