Lactobacillus during Fermentation
The lactobacillus grows while the yeast grows and stops growing when the yeast stops growing.
A pure culture of lactobacillus will only get acclimatised to a symbiosis with yeast if, when first introduced to the yeast, there is far more lactobacillus than yeast.
Lactobacillus and yeast during fermentation in a practical environment
The proportion of yeast to lactobacillus is 4:1, 5:1 or 6:1
At the start of fermentation, the yeast grows much quicker, but the lactobacillus catches up later and by the end of primary fermentation the proportion of yeast to bacteria is the same as when pitched.
Towards the end of fermentation, most of the bacteria rises into the yeast head. After five days fermenting, 96% of the lactobacillus is in the head, just 4% in the beer.
Here's a chart to show how the fermentation progresses:
The warmer the fermentation temperature, the faster the lactobacillus grows. Though, whether fermented warm or cold, the ratio of yeast to bacteria at the end of fermentation always returns to about what it was at pitching time.
Despite consisting of two totally disparate elements, the pitching culture behaves like a single strain.
Weissbier fermented at 18.75 - 25º C is sourer than that fermented below 18.75º C.
Sourness in the fermenting tun is almost all formed between the start in growth of the lactobacillus and when the yeast floats to the surface, when the lactobacilluuus rises to the surface with the yeast.
About half the sourness in a 3-4 week old bottle was formed in the fermenting tun during the first 3 days of fermentation.
If primary fermentation occurs at a temperature below 16.25º C, the growth of lactobacillus is so slow that only an insignificant amount of sourness can be produced.
So much good stuff there. I hope you can digest it all. No, don't spit it out again. That's disgusting. I haven't finished with fermenting yet, anyway.