I usually brew 3 gallon BIAB batches, but for various reasons I want to brew a bigger batch in the next week, and I don't have the capacity to do it in a single brew. I'm planning on just brewing two batches back to back and fermenting them together, but I'm not sure when to pitch the yeast. Should I pitch into the first batch as soon as it's cooled, to prevent any spoilage organisms that might have found their way into the wort taking hold? Or should I wait a few hours until I've finished the second batch, and pitch the yeast into both? I'm wondering if adding fresh wort a few hours later will affect the way the yeast grows, which might in turn affect the flavour in the final beer.