I just kegged a cider last week (second week of April) that I had been aging in a 3 gallon glass carboy since about November. I observed what I'm fairly certain were signs of malolactic fermentation: although the headspace was minimal, there was a clear pellicle with bubbles that appeared a couple of days before I decided to transfer; there were some sparse tiny bubbles rising from the bottom of the carboy; the cider tasted clean, very dry with a balanced acidity, and might be my best cider yet. The appearance of this fermentation also coincided with the appearance of apple blossoms in the trees around my house, which others have noted about MLF (not that they are necessarily connected). I initially thought it was infected and decided to rack it, then after reading a bit realized that I probably could have let it ride. I transferred some cider back out of the keg to a 1/2 gallon jug to see if I can restart MLF, and compare this to the cider that stays under refrigeration.
Other info: I added 3 crushed campden tablets to 4 gallons of juice (OG 1.053) 24 hours before pitching the yeast; I used D47 yeast, rehydrated with Go-Ferm; left the cider on a small layer of lees throughout secondary; kept the carboy in a closet that maintained a pretty steady 59-60 F temp; fermented to dry (SG 0.998); the gravity was the same at the beginning and end of secondary (i.e. after the observed MLF started); used an S-shaped airlock which showed that there was positive pressure in the carboy for the duration of secondary (as evidenced by the liquid level pushed outward in the airlock), indicating that there was no ingress of air.
My question is, where did the bacteria that started MLF come from? I believe my sanitation is pretty effective, although I suppose at each step there was a chance I didn't take out 100% of the bugs around this batch. I also was very careful to prevent any outside air from reaching the cider, and there is no evidence of oxygenation, great apple aroma, etc. Basically the only thing I observed changing in the conditions around the carboy was that the temp might have risen a degree or two, tops. Much of the reading I've done has mentioned the potential for MLF to start spontaneously in the Spring, but I haven't come across any discussion of exactly how this happens, and I'm just curious from a scientific standpoint as to how this can occur.
Other info: I added 3 crushed campden tablets to 4 gallons of juice (OG 1.053) 24 hours before pitching the yeast; I used D47 yeast, rehydrated with Go-Ferm; left the cider on a small layer of lees throughout secondary; kept the carboy in a closet that maintained a pretty steady 59-60 F temp; fermented to dry (SG 0.998); the gravity was the same at the beginning and end of secondary (i.e. after the observed MLF started); used an S-shaped airlock which showed that there was positive pressure in the carboy for the duration of secondary (as evidenced by the liquid level pushed outward in the airlock), indicating that there was no ingress of air.
My question is, where did the bacteria that started MLF come from? I believe my sanitation is pretty effective, although I suppose at each step there was a chance I didn't take out 100% of the bugs around this batch. I also was very careful to prevent any outside air from reaching the cider, and there is no evidence of oxygenation, great apple aroma, etc. Basically the only thing I observed changing in the conditions around the carboy was that the temp might have risen a degree or two, tops. Much of the reading I've done has mentioned the potential for MLF to start spontaneously in the Spring, but I haven't come across any discussion of exactly how this happens, and I'm just curious from a scientific standpoint as to how this can occur.
