It's usually best to have a starter that has been refreshed a couple times (atleast 3) immediately before baking. It's preferable to refresh the day before or the day of baking. Refreshing can also be referred to as 'building'. This usually requires being around the house to watch it and feed it often.
To prepare your starter before baking for an optimally active starter:
To prepare your starter you should feed it it's exact amount, ie a 1:1 ratio, 3 times the day before baking. So for example, take 1/4 cup starter, feed it 1/4 cup flour and slightly less than 1/4 cup water (or it gets too soupy) in the early morning. Feed it 1/2 cup at lunch, then before bed, feed it 1 cup. If you need more than 1 cup, start with a greater amount in the morning (takes a little mathematics but you'll get the hang of it!). The next morning you're starter will be very active and ready to be put into your recipes to bake with! You can store this for a few days in the fridge, but at that point you really should refresh it this same way again before using it.
To prepare your starter before baking for a decently active starter:
For a more simple, less time consuming option, you can use your refrigerator with the guidelines below.
Note: If your starter is in between stiff and wet, simply ignore the approximate times and follow the volume amounts in the guideline to know when it is ready.
Stiff starter (doughy/putty consistency - more flour used)*
• 1 day before baking: feed, let sit out until about 1 1/2 times larger in volume/size (about 2 hours).**
• 3 days before baking: feed, let sit out until about 1 1/4 larger in volume (about an hour).
• 1 week before baking: feed, let sit until its increased just a bit in volume (about 30 minutes).
Wet starter (pancake batter consistency - more water used)***
• 1 day before baking: feed, let sit out until about 1 1/2 times larger in volume (about 5 hours).**
• 3 days before baking: feed, let sit until about 1 1/4 larger in volume (about 3 hours).
• 1 week before baking: feed, let sit until its increased just a bit in volume (about an hour)
If no particular consistency is called for in the recipe, aim for a happy medium: a starter that feels like a very thick pancake batter, and is still stirrable. Stiff and wet starters are difficult to pinpoint when they are active because neither rise very well. You may want to experiment with these after getting the hang of a 'normal' middle-ground consistinency starter which has both the wetness to expand and the stiffness to bubble and rise.
* a stiff starter is used for mild breads, some recipes will call for a stiff starter. These also tend to have more yeast active, and less bacteria.
**Sourdough will rise quicker in the summer, and slower in the winter, try following the volume amounts until you can determine the best amount of time.
***Wet starters are known to make a more sour tasting bread. The watery nature encourages more bacteria and their sour acid by-products.