Cook low, flavor high
• Start with cold water. Hot water might activate some ingredients before you want them activated, and it can counteract extraction of collagen because hot water might seal it into the bones.
• Stocks are simmered gently, with bubbles just breaking the surface, and not boiled. If a stock is boiled, it will be cloudy.
• Salt cautiously. Since most stocks are reduced to make soups and sauces, they will become richer and saltier in that process.
• Skim often. The scum that forms on the surface should be removed to avoid bitterness and impurity.
• Fat can be removed after the stock is finished and cooled. Fat floats, separates and solidifies. It can be easily removed once the stock has cooled.
• Stocks can be frozen and kept indefinitely but are better fresh.
• If the stock hasn't been used upon its fourth day, bring it to a boil to extend its shelf life another three to four days.