This is Tapai or fermented tapioca. It is rarely found in Singapore. Tapai juice taste like sweet wine or a bit like the Japanese rice sake. You may find it the 1950s and 60s but not these days. I love tapai and had not tasted one since I was a kid. I found it at a pasar malam and gladly bought 2 for $2.
You may also eat the yummy fermented tapioca.