This article relies largely or entirely on a single source. (November 2015)
A master stock (Chinese: 鹵水 or 高汤) is a stock which is repeatedly reused to poach or braise meats. It has its origins in Chinese cuisine and is typically used in Cantonese and Fujian cuisines. Foods poached or braised in the master stock are generally referred to as lou mei.
The base of a master stock is made from typical Chinese ingredients, namely water, soy sauce, rock sugar and Shaoxing or rice wine. A variety of other spices and flavourings are usually also added, such as spring onions, shallots, star anise, dried citrus peel, cassia bark, sand ginger, Szechuan pepper, garlic, ginger, and dried mushrooms.
Once the base stock has been prepared, it is then used as a poaching or braising liquid for meat. Chicken is the most common meat that is cooked in a master stock, although squab, duck, quail, and pork are also often used.
The defining characteristic of a master stock from other stocks is that after initial use, it is not discarded or turned into a soup or sauce. Instead, the broth is stored and reused in the future as a stock for more poachings sometimes for up to 100 years. With each use, the poached meats and other ingredients absorb the stock's flavour while imparting their own back into the stock. In this way, over time, flavour accumulates in the stock, making it richer and more complex with each poaching, while subsequent poached meats absorb this flavour and likewise become more flavourful.
In theory, a master stock could be sustained indefinitely if due care is taken to ensure it does not spoil. There are claims of master stocks in China that are hundreds of years old, passed down through generations of cooks in this way.
After use, if the master stock will not be immediately reused, it is usually boiled, skimmed, strained and cooled quickly to kill any microorganisms in the stock. The growth of microbes in the stock can potentially spoil the flavour of the stock or pose a health risk. The stock is then refrigerated or frozen until required. Refrigerated stocks may be kept for up to three days, while frozen stocks may be kept for up to a month. If the stock is to be kept longer it must be boiled before being returned to storage.