There are a number of beef stock substitutes, so in order to choose the best one, you will need to consider your particular needs. If you have no objections to using a beef-based product, and just cannot find actual stock, it is possible to use beef bouillon cubes in most recipes that call for beef stock. You can also use various other stocks, such as chicken or vegetable, though the flavor of your dish will typically be different. If you need a good beef stock substitute for a vegetarian dish, you may want to consider using vegetable stock with some autolyzed yeast or yeast extract added. Various dehydrated powders, such as onion soup mixes, can also be used as a satisfactory beef stock substitute when making vegetarian soups.
Beef stock is produced by simmering beef bones and meat in water to extract the flavor. The solid materials are then strained and removed, resulting in a watery, flavorful substance that can be used in making sauces, soups, and many other dishes. A similar process is also used to make stocks out of other meats, and vegetarian stock can also be made out of vegetables. Commercially produced stocks are readily available if you do not wish to simmer your own, as are a range of potential substitutes.
The best beef substitute is beef bouillon cubes, which are actually dehydrated stock. If you cannot find stock and do not wish to make your own, these cubes can be used as a beef stock substitute in nearly every case. This will typically result in a dish that tastes the same as one made with actual stock, though beef bouillon can be very salty. It is also possible to use chicken stock or bouillon in many cases, though this will result in a different flavor that may not work in some dishes.
You also have a number of options for a beef stock substitute if you are making a vegetarian dish. The primary vegetarian substitute for beef stock is vegetable stock, though you may find this does not provide you with the same type of savory flavor. One way to make vegetable broth into a better beef stock substitute is adding yeast extract. If you are making soup that calls for beef stock, you can try using an onion soup mix, though a little soy sauce is another option to consider. It is also possible to simply substitute water for beef stock in some recipes, though this will typically result in less flavor.