Lipase vs sour thawed milk

mlynne37wiu

I thawed a bag of milk from early September last weekend in the fridge and when I transferred it into a bottle it smelled soapy. My husband fed DD and she drank it [he said she downed it quickly but then had a meltdown when she was all done, so I am wondering what that was about], but I don't think that any of the other milk I've thawed smelled like that. I'm back to work tomorrow and I'm thawing bags today, so I'm hoping they're ok. My question is, how do you know if milk is smelly because of lipase or if it's smelly because it's sour and has gone bad? The milk isn't in the fridge for longer than 24 hours before consumption.