Leaving stock unseasoned gives you maximum control over the final salt content of your dishes, preventing over-salting as you reduce the stock or combine it with other ingredients. This allows for greater flexibility and better flavor balancing.
When you make stock, you're essentially extracting flavors from bones, vegetables, and aromatics. If you add salt during this process, the salt concentration will increase as the stock simmers and reduces. This means that the final saltiness of the stock can be unpredictable.
By leaving the stock unseasoned, you can add salt later, when you're actually preparing your dish. This allows you to taste and adjust the seasoning as needed, ensuring that the final product is perfectly balanced. Different recipes require different levels of salt, and some ingredients, like soy sauce or cheese, already contain a significant amount of salt. Starting with an unseasoned stock gives you the freedom to account for these factors.
Imagine using a pre-salted stock in a soup that also contains salty vegetables like celery or olives. The result could be an overly salty and unpleasant dish. Unseasoned stock provides a blank canvas, allowing you to build flavors precisely to your liking.
Always taste your dish frequently as you add salt. It's much easier to add more salt than it is to remove it. Start with a small amount and gradually increase until you reach the desired flavor.