Big bakeries do things differently than the average home baker. I know they use various methods for maintaining their mother, but I've never worked in a bakery so I'll just tell you how I do it.
I use a maintenance method that requires no regular feeding, no discarding, and is always ready to bake in 12 hours.
I maintain a stiff 66% hydration starter - made my mixing of 8 grams starter, 56 grams flour, and 37 grams water, for a total of 101 grams. This stiff starter will say healthy in the fridge for up to 4 months with no feeding, stirring, etc. It's really hands off.
When I am going to bake, I take about 8 grams of the starter and mix with 50 grams flour, 50 grams water. This is a levain. I put it in my proofing box (a cooler with a heating pad and temp controller) running at 80F and it is fully active within 12 hours, often less. I will typically make the levain at 9PM and then use it to make dough at 9am the next day.
Since I am only using 8 grams at a time, the 100g starter in the fridge will make about 10 loaves. When I get down to about 15 grams, I build the starter back up as in the first step.
The 100 grams of starter fits nicely into a 8oz ball jar. I use the same size for the levain as well. If you bake frequently, you can maintain a larger starter, or just rebuild more often. I've been using this method for over 2 years with starter that I've had for about 5.
Here's the levain after 10 hours.
