steam is *not* always the same temperature
I’ve been reading through the forum archives and have come across several threads where steaming methods were discussed, and the statement has been made that “steam at atmospheric pressure is always at the same temperature”, and I haven’t seen anyone refute this. As understanding steam is important for crusts, I thought it was important to set the record straight on this, and rather than resurrect old threads, I thought it’d be worth starting a new discussion.
In short, it’s not true.
Steam is the gaseous phase of water. Liquid water at atmospheric pressure can never go above 100C/212F, because at that temperature it starts to change phase, and all energy put into it is swallowed up in the power-hungry process of phase change. But once the water is fully converted to steam, it can get hotter, and it does – this is called ‘superheating’.
Why this is important is in the difference between a pan of water in your oven and the ‘live steam’ I believe bakeries use, which is injected from a pressurized boiler. Our pans of water at home are producing a mixture of steam and vapour, not pure steam. Vapour can’t top 100C, and the steam produced by this process won’t be much over it, either. But steam injected from a boiler will be pure steam, no vapour, and is likely superheated. So its effect on the crust will be that much more dramatic.
I hope this helps.
Source: Fresh Loaf