Yes, almond milk can spoil if left at room temperature for more than 2 hours, just like regular dairy milk. The signs of spoilage will be different, though. Regardless if the almond milk you purchased was shelf-stable or stored in a refrigerator, once opened, it should be kept in the fridge. If your almond milk is shelf-stable and unopened, check the carton for bloating or deformities. These are a sure sign it's not safe to consume and should be thrown out. Other signs your almond milk is spoiled include a slimy texture or clumps and if you see anything like that you should definitely discard it.