Lactobacillus brevis - keg souring

Several days ago I pitched about 5 billion (gross estimate!) L.brevis cells into 19L of wort. OG was 1.048. The dedicated sour keg's headspace was subsequently purged several times with CO2 and left at 18C to sour.

After 3 days, a preliminary tasting was done. It was just worty, with absolutely no sourness. I started freaking out, thinking I've killed the Lacto! Then it struck me that Lacto probably does better at higher temps (think human body temps, since they love wriggling about in our intestines anyway). So the sour keg was taken out and placed at Singapore 'room temp' (ie minimum 29C probably). It receives direct evening sun from 3-6pm, which will probably warm it up to a very toasty 30+ degrees C. 

A second tasting was done at Day 6 (3 days after elevating temps). It still smelt very much like wort, unlike the previous sour mash attempt which was nauseating. There was a noticeable sourness to it, but not as strong as I'd have liked it. I'll liken it to drinking a young kombucha at 4 days old, or about the perceived acidity of commercial orange juice. 

To be honest, I was expecting more from L. brevis. Various sources list it's acidity to be sharper, but it's possible I didn't leave it out long enough. Alternatively, it is also possible that it has consumed much of the easily-fermentable monosaccharides present and will take some time to break down the more complex sugars in the wort. 

I will be pitching a 500ml slurry of WLP090 (San Diego Super Yeast) into it on Day 7. This will be left to ferment for 4 days or so at 18C (WLP090 has a VERY narrow range of fermentation temp!), and in the meantime I'll be stepping up some Brett. bruxellensis to be added as a 3rd and final addition, at which time the keg will once again be allowed to warm up to ambient temps. The purpose of the Brett addition is not quite to produce barnyard funkiness, but rather to help break down complex sugars and dextrins for both WLP090 and the Lacto, and also to metabolise some of the not-too-pleasant by-products from Lacto fermentation. The source lab for L.brevis got back to me and apparently this strain can handle up to 10% alcohol, so I'm hoping that the Lacto will continue to proliferate even into the aging phase, so as to produce a sharper acidity. 

Crossing my fingers and hoping that this process works. I'm planning to bottle half, and age out the rest on lightly toasted oak cubes. The oak cubes can then be dried as a source of future inoculant for this blend..