Sourdough is a living thing. As such it can be unpredictable and constantly in flux due to changes in its environment. Most sourdough problems can be easily remedied or are not worth worrying about. Even so, you may wish to address these issues.
Reviving a Hibernated Starter
If you’ve allowed your starter to come to a hibernated state in which it doesn’t appear to have much life, then you’ll need to revive your starter. Your culture may look lifeless, but on the microscopic level you will most likely find life so you will just need to give it a little extra TLC.
This means more than just feeding it. Sourdough should have more of yeasts than lactobacilli to be effective in making good breads. So you’re going to need to give it some special care in order to build the yeasts up in your starter.
To jumpstart a starter that looks lifeless, take a small amount of the hibernating starter (just a few tablespoons) and bring it to room temperature. Now feed it eight times as much flour and five times as much water as the amount of starter that you are starting with.
For instance, if you have 2 tablespoons of starter, use 16 tablespoons of flour (1 cup) and 5 tablespoons of water.
Repeat this twice a day, in 12-hour intervals, and start each feeding by discarding half of the starter.
By giving the starter large feedings of flour you should be able to revive it in a way that will tip the present organisms in favor of the yeast.
If the Starter Smells or Tastes of Alcohol
One of the organisms present in a sourdough culture is alcohol. While this is normal, too much is definitely not a good thing and can be a sign that you need to change the way you are caring for your starter.
Too much alcohol in your sourdough usually means that you are not feeding your starter frequently enough. Increase the frequency of feeds (every 8 hours instead of every 12, for instance) and see if that resolves the alcohol flavor or smell of the starter.
Getting the Starter Bubbly
What you want to see in a sourdough starter is happy, bubbling activity. This is an indication of health in that the organisms in ther sourdough culture are feeding off the flour you give it and creating gases (bubbles).
If your starter is not bubbly then you’ll want to feed it and allow it to go through its bubbling/proofing period. After you feed it you should see bubbling action within 4 to 12 hours. Feed it again at 12 hours to make sure your culture is getting enough food.
If, after several feeds, you still do not see bubbling action your starter may be damaged or even dead. If that is the case, sadly you may want to start or acquire a new one.
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 – food or soap residue – or weakened yeast due to a forgotten feeding.
When you find mold you can try to salvage your sourdough starter or you can start over. Please exercise good judgment when salvaging a moldy starter. It is one thing if the mold is only infecting the surface, but an entirely different problem if it is penetrating the whole starter below the surface.
If you decide to save the starter you will first want to remove the mold from the surface. Next, using a new (clean) utensil, remove a small portion of the sourdough that wasn’t near the mold. One tablespoon will suffice. Put that tablespoon into a new very clean container, and add equal parts flour and water (by weight). If you are measuring by volume, use one part starter, one part water, and slightly less than two parts flour. Mix, cover with a breathable lid, and allow to proof.
Once proofed, or within 12 hours, feed the starter again using the same ratio (one part flour, one part water by weight; or one part water, almost two parts flour by volume). Continue to feed for several days and watch carefully for any signs of mold. If all goes well and there are no more signs of mold or off smells, then you should be able to use it in baking or store in the refrigerator.
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.