Give your starter a good long look. This might be the day of your first harvest.
One thing to check out is whether the bubbles are just on top, or whether there are bubbles throughout the jar. The frothy feeling yesterday was a good sign, and now when I look at the side of the jar, my starter is showing bubbles throughout.
Pay careful attention to what happens after feeding and stirring. The mixture should rise in the jar when you're done. If you've got a small jar and a lot of starter, you might find starter crawling all over your countertop in the morning.
I've seen this more than once when a starter has decided to become very active during the night. This is why you don't want to seal the jar tightly. It's better that starter oozes out gently rather than causing a small explosion.
Since my starter is looking quite active on Day 9, I went ahead and removed 4 ounces of the starter and put it in a bowl. I added 2 ounces of flour and 1 ounce of water, stirred it, and covered the bowl. Leave this mixture on the counter overnight, and you can actually bake with it tomorrow! (Make sure you have bread flour, kosher salt, and olive oil on hand for tomorrow and you'll be ready to bake your first sourdough bread!)
Meanwhile, the starter in the jar gets a meal of its usual one ounce each of water and flour.
If your starter isn't quite active enough, and you don't see bubbles up and down the side of the jar, don't despair. You can keep feeding it until it's ready. If the jar's too full to keep feeding, you can take a little over a cup out and use this proto-starter in a not-quite-sourdough bread.
Go Back in Time...
Day Zero: What You'll Need »
Day 1: A Half-Ounce Flour and an Ounce of Water »
Day 2: No Feeding, Just Stirring »
Day 3: Feed Me More Flour! »
Day 4: 100% Hydration »
Day 5: Keep Feeding and Stirring! »
Day 6: Keep Stirring and Feeding! »
Day 7: Feed and Wait »
Day 8: Getting Close! »