How long can lacto. delbrueckii survive?

I have a batch of berliner weisse that's three months into aging, and I just took a taste sample. There's not really any sourness at all detectable (kind of a bummer). I was thinking of using some lactose to see if I can jump start any lactic acid formation (lactose so that the yeast don't gobble it all up). Would the lacto still even be floating around, healthy, looking for things to eat? I would imagine that there probably hasn't been any sugars for the lacto to munch on for awhile now. Do you think it would show any activity at this point, or is the lacto just not going to be reactivated?

I'd hate to pitch in some lactose and just unintentionally sweeten the beer up too much... it's otherwise a damn good beer (not a single off or bad flavor), and would make a fantastic base for fruits.

In my experience, I get the best sour flavors from lactic acid around 6-12 months. Three months isn't much time. Lactic acid will continue to work for up to 18-24 months.

So your advice would be to give it some more time, then?

It is typical to have practically no detectable sourness at 3months?

Lacto can take what seems like forever to get good and sour. Way too long for me, so now I just do a sour mash and I get all the goodness of a BW without waiting a year.

Wow.. just hitting almost the fourth month with it and it's starting to get some nice pellicle action. Can't believe the lacto is still kicking in there! Can't wait to see how the batch turns out.