The bacteria present in sourdough cultures produce lactic and also acetic acid. If you notice your sourdough is smelling/tasting more like yogurt, your starter is likely balanced more towards lactic acid. If your sourdough is smelling/tasting more like sharp vinegar (I always pick it up as a strong cider vinegar aroma), this means you’re balancing more towards acetic acid. A starter re-fed at peak each time will tend to have a lower acidity overall, and less of a sharp tanginess. A starter chronically under-fed (repeatedly feeding after the starter has peaked and fallen/collapsed) will yield a starter with more concentrated acid burden and a more sharp sour tanginess. Starters that are fed at peak and are not burdened by a high acid concentration will tend to have better yeast (rise) activity, as high acidity can stress the yeast population.So, if you’re looking for a sweeter/more mild flavor profile and more robust rise activity, consider feeding at lower ratios (1:1:1) and keeping the starter nice and warm (try to feed again right when the starter hits peak); If you’re looking for more sour tanginess to your starter, consider feeding at higher ratios (1:10:10) and allowing a longer duration between feeds.For more advanced-level detail into the balance of sweet and sour starters and how to optimize your starter behavior, see my pre-recorded workshop here: https://www.airsubs.com/pros/full-proof-baking/on-demand/sourdough-starter-levain-201