HOW DO I KNOW IF MY STARTER IS AT ITS PEAK/READY FOR HARVEST?
Basically, you want to use your starter when it is fed and at its peak. That means taking your tablespoon of starter from your starter jar at its highest point of rise. This is where the rubber band on your starter jar is helpful. You can see when the starter has doubled or even tripled depending on how warm your kitchen is. You can also see (due to the glass container) that the starter is bubbly and active. Harvest your starter at its peak bubbliness (not when it has started to fall). I like to take a rubber band or dry erase marker and mark the point on my starter jar where it has typically been reaching at its peak. That way I have a good general idea about when I can harvest a bit of my starter for dough making. For me, if I am double feeding, and my second feed is around 2 pm, that is usually at 8 or 9 pm. But this is where you have to get to know your starter and your schedule. This is a good primer on what makes a strong starter and how to know when it is ready.
NOTES ON MAKING A LEAVEN (LEAVAIN)
A leaven or leavain is just a small bit of starter that has been well fed and harvested at its peak and then fed again – like a superfeed. This additional feed gives your dough that extra kick – the strong and active super-fed starter will have the power to help your dough rise beautifully. I make the leaven according to the same instructions on the Kitchn blog, using all AP flour. I generally make my leaven at night at around 8 or 9 pm (before bed). I make it in a large glass and cover it loosely with a small plastic Tupperware top. I keep it next to my mason jar of starter, under the kitchen cabinet light.
DO I REALLY HAVE TO DISCARD BEFORE A FEED?
Yes. I know this seems counterintuitive but you will be drowning in starter that you still have to feed if you do not. Remember that when you feed your starter, you are doing it with an amount of flour and water that is proportional to the weight of your starter. So, if you do not discard, you will have to feed your starter more and more flour and water to make sure you are feeding it enough food. Without discarding, your starter will grow exponentially and will in the end require you to waste more flour than if you continue to discard before feed to maintain a consistent starter weight. Check HERE for awesome ideas to bake with your discard. Or make a baby starter for a friend and teach them to bake!