Use a more mature starter
Feed the starter less frequently
Keep the starter at a cooler temperature
Use a higher hydration starter
Increase the prefermented flour percentage
Extend the bulk fermentation
Retard the dough in the refrigerator longer
Use a stiffer starter for more acetic acidity
Use whole grain flour in the starter or dough
Reduce the amount of commercial yeast, if used
Refresh the starter with less frequent, larger feedings
Let the starter peak and then fall before using it
Build flavor with multiple levain refreshments
Use a lower inoculation and longer fermentation
Ferment dough at cooler room temperature
Keep the dough covered during long cold proofing
Use rye flour in small amounts
Avoid overfeeding the starter before baking