Originally Posted by Oldsock
Sour mashes are hard to predict. Try to keep oxygen out, purge with CO2 if at all possible. Other than that, taste as you go. You can measure the pH too. The big issue with pre-souring is that if you get too sour, you're primary yeast won't be too happy.
Raspberries are a tough fruit to brew with, their aroma is awesome, but it is hard to get a saturated fruit flavor. I just racked 4 gallons of sour brown onto 15 lbs of defrosted raspberries.
Yhea, that was the big interrogation point for me, the level of sourness. I can't really go by taste and brew when it's OK, because I have a busy schedule and I'm brewing at a predicted time.
I think I might go with a partial sour mash. I will sour 4 ou 5 liters (for a 20-22L final), which I'll be able to maintain around 100-110°F for a good 3 weeks. Then I'll be able to use this sour part to adjust my mash pH, and then add the rest of it at sparge.
That way, if the sour mash turns out bad, I will not have scrap an entire batch, I could brew the beer anyway.