Just like cow milk, nut milk isn’t sour, which means that the acidity (pH) is relatively high. When performing a correct risk analysis, you will conclude that there is a potential hazard for food safety, caused by growing spores of pathogenic bacteria present in the nut milk, which can make consumers seriously ill.

That is why sterilization is often chosen to kill the spores, still making the product safe. This gives the product without cooling an almost endless shelf life, but the taste will have deteriorated significantly.
Another option to produce safe nut milk is by adding fruit. The combination of nut milk and fruit lowers the acidity, and in addition tastes great.