Which is how RWBY and JNPR were able to do the food fight.
The bread that Blake and Pyrrha used wasn't hard as a rock. They used their Aura to protect it from damage. As soon as they were done with it, it broke, with the exception of the two that Pyrrha threw at Ruby.
With the ones that Pyrrha threw at Ruby, she may have made them continue having an Aura coating after they left her hand, which makes sense for someone like Pyrrha whose weapon has a form that can be thrown. She wouldn't want her javelin to become damaged when she throws it at an enemy, so she may have been practiced in leaving a lasting Aura coating on a thrown weapon, which fades after a certain amount of time. This would also be why Ren's leeks stabbed into the floor. We had already seen by that point that Ren is more practiced in Aura manipulation than most Huntsmen, to the point that he can create localized shields and also weaponize it through martial arts.