Those of you who, like me, have a wood fire will know that different woods burn hotter than others, some spit and some give a long slow burn. Medieval cooks knew a lot about wood in all its various categories. Bowls for keeping meat or mixing were always made of sycamore: its close grain ensured it didn't harbour germs. Bowls of willow wood were ideal for keeping liquid marinades. Ash was ideal for a kitchen fire as well as for tool handles. The light-coloured woods of beech and lime were used for dairy work and butter tubs. Birch twigs could sometimes be laid in the bottom of cooking pots and the meat placed on top when making soups and stews to stop it from sticking. Oak was crucial for medieval buildings, but oak chips played their part in cooking: they were perfect for smoking. ...I don't know about the idea of using sycamore because of the germs, although that's a side effect we could appreciate now with our advanced scientific understanding. I can see that a close grained bowl would be good for meat or mixing because it wouldn't absorb liquids and would be usable much longer. No one wants a soft wood bowl for keeping a piece of meat in.
Clarissa Dickson Wright,
A History of English Food (The High Middle Ages)