Managing the sourness in your sourdough is a biological balancing act between lactic acid (creamy and mild) and acetic acid (sharp and vinegary) that you can calibrate by adjusting your fermentation environment. To achieve a more assertive tang, you should use a past-peak starter, incorporate mineral-rich whole grains like rye to buffer acidity, and extend your cold proof in the refrigerator for up to 48 hours to favor acetic acid production. Conversely, if you prefer a milder, buttery profile, focus on using a “young” levain before it reaches full ripeness, shortening your overall fermentation timeline to prevent acid buildup, and maintaining a frequent feeding schedule to ensure your starter remains sweet and vibrant. By treating variables like temperature and hydration as “levers,” you move beyond following a recipe to intentionally designing the flavor profile of every loaf you bake.