Season lightly at the beginning, erring on the side of under-seasoning. Taste and adjust seasoning incrementally as the broth reduces, adding more salt or other seasonings as needed.
When preparing a broth or sauce that will undergo reduction, the concentration of flavors, including salt, will increase significantly as water evaporates. If you season aggressively at the start, the final product will likely be far too salty. Here's a step-by-step approach to avoid this:
Initial Seasoning: Begin with a very light hand when adding salt and other seasonings. It's always easier to add more than to remove excess salt.
Simmer and Reduce: Allow the broth to simmer and reduce to your desired consistency. This process concentrates the flavors.
Taste and Adjust: Once the broth has reduced, taste it carefully. Add salt a little at a time, stirring and tasting after each addition. Also, consider other seasonings that might enhance the flavor profile, such as pepper, herbs, or a touch of acidity (lemon juice or vinegar).
Final Adjustment: Continue tasting and adjusting until the broth reaches the perfect balance of flavors. Remember that the flavors may continue to develop slightly as the broth cools.
If you accidentally over-salt a broth that is reducing, you can try adding a peeled potato to the broth during the last part of the simmering process. The potato will absorb some of the excess salt. Remove the potato before serving.