Spontaneous mother in Pocari Sweat bottle. What is this?

[tenagasuryafisk]

Hello,
I live in the tropics and my house is open with no air conditioning. I left a big bottle of Pocari Sweat on the fridge to drink when needed and today after about 2 weeks as I went to pour some into a glass, I discovered a huge dense white mother floating in it. The bottle has been left with the lid on. What could this possible be?!