Overfeeding a sourdough starter can be beneficial because it provides an abundance of food for the culture, which can increase it's activity and fermentation.  Just like people, your sourdough starter can be extra hungry -- especially in times where there is higher fermentation rates. This is particularly helpful when you notice that your sourdough starter isn't as active as it once was.  In typical Summit Sourdough fashion our starter is known for regularly quadrupling in size with proper care and maintenance.  When you overfeed a starter, the culture will multiply more quickly, leading to a stronger and more active starter.

It's important to note that overfeeding can also have negative effects on a sourdough starter if done excessively or too frequently. If the starter is overfed, it can become too acidic or develop an unpleasant odor which is the result of excess food rotting in the jar.   For this exact reason, it is important to allow your starter to eat for 24hours when an overfeed is done.  You should not remove starter to bake with, and you should not feed again before the 24 hours is up.  This allows ample time for the starter to consume the food without risking of diluting the strength.

Reasons your Sourdough Starter Might be Sluggish

• Feeding schedule: A sourdough starter needs to be fed regularly to maintain its activity. If it is not fed often enough, the yeast and bacteria will become weak and the starter will become sluggish.  I recommend you feed once every 24 - 30 hours, every 24 hours is better.
• Flour: The type and quality of flour used can also affect the activity of the sourdough starter. Using part rye flour can help to give the starter a boost because it contains more nutrients that the culture needs to thrive.  I'll discuss how to do a proper Rye Boost in a separate post.  I do not suggest a 100% Rye flour feed
• Water: Chlorinated water can kill the beneficial bacteria in the sourdough starter, so it's important to use non-chlorinated water when feeding the starter.
• Contamination: If the sourdough starter becomes contaminated with bad bacteria or mold, it can become sluggish and not produce the desired results.

To overfeed a sourdough starter, simply increase the amount of flour and water used in each feeding. For example, I suggest that Summit Sourdough is fed at a 1:1:1 ratio by weight in grams (100g starter : 100g water : 100g flour).  To offer your starter an overfeed, i suggest a 50% increase in the water and flour added to the starter. An example of a proper overfeed would be:
100g starter : 150g water : 150g flour

It's important to monitor the starter's activity and adjust the feeding schedule as needed to ensure it stays healthy and active.  In some rare cases, it's okay to up this to a 100% overfeed.  100g starter : 200g water : 200g flour

As a reminder, doing this too often will be detrimental to your starter.  I suggest an overfeed no more than 2x per month.   Otherwise, keep on your regular feeding schedule of 1:1:1 by weight in grams.   If you still need more of a boost, consider a rye boost.