Sourdough is a living thing, reacting to changes in its environment. Usually, minor adjustments to feeding frequency or temperature will keep a sourdough starter healthy and active. However, there are a few situations that might require some extra care.
Boosting a Sluggish Starter
Healthy sourdough starter should be bubbly and active. The organisms in the sourdough culture are feeding off the flour and creating gases (bubbles). After feeding, bubbling action should be visible within 4 to 12 hours.
If a sourdough starter is not bubbly, it may require more frequent feedings. If feeding every 12 hours, increase to feeding every 8-10 hours, to make sure the culture is getting enough food.
Check the temperature in the culturing area. Sourdough likes a temperature between 70°F and 85ºF, around the clock. To make adjustments in cold or warm weather, try the tips in these articles:
Reviving a Hibernating Starter
A sourdough starter that has gone into hibernation or does not appear to have much life, may be able to be revived. A culture may look lifeless, but on the microscopic level there may be life, so the starter can be recovered with a little extra TLC.
To jumpstart a starter that looks lifeless:
Rehabilitating a Starter with an Alcohol or Nail Polish Aroma
When sourdough starter isn't fed often enough or feedings are skipped, it will begin consuming discarded yeast, as well as its own waste, leading to the unpleasant aroma of alcohol or nail polish remover. The best way to prevent this from happening is to feed the sourdough starter more often.
If increased feedings do not solve the problem, remove 2 tablespoons of starter and feed with ¼ cup water and ¼-½ cup of flour. When it is time to feed the starter again, resume normal feeding amounts.
Dealing with Mold
While mold on a sourdough starter is fairly rare, it does happen from time to time. The cause is usually some sort of contamination with food or soap residue, or weakened yeast due to a forgotten feeding.
If mold does appear, it may be time to discard the starter and begin again with a new starter, or it may be possible to revive the starter. Exercise good judgment. If the mold is only infecting the surface, reviving the starter may be appropriate. If mold is penetrating the entire starter below the surface, discard and obtain a new starter.
Instructions for Recovering a Moldy Sourdough Starter:
Remember that sourdough is a living thing that can be unpredictable. Thankfully it is also a fairly resilient thing that can often be brought to life even after the biggest of trials.