The water bath

How to tell it is going right

• The water stands two thirds of the way up the side of the inner dish and is still standing there at the end: filled only to the halfway mark, the upper band sets hard and pale long before the centre moves, and water lapping the rim or splashed over the top has thinned the surface into a loose, watery skin.
• The bath is silent, steaming, with at most one slow bubble rising at the wall of the outer vessel, held between 80C and 85C (176F and 185F). Any chatter of the dish against the base, any steady string of bubbles, any rolling of the surface means the water has run to 100C (212F) and the damage is already done.
• Nudged, the centre trembles as one piece, a coin of movement in a face that is otherwise still. A ripple that travels outward in waves means it is still liquid beneath the skin; a face that does not move at all has been carried past the set and will eat firm and grainy.
• Cut, the face is dense and glossy from edge to edge: no honeycomb of small bubbles along the outer band, and no bead of clear liquid weeping from the cut or pooling between the set and the side of the dish, which is the mark of protein wrung out by heat.
• It left the water before it was done and rested clear of it: the centre reads 78C (172F) as it is lifted out and climbs to roughly 82C (180F) standing. Anything left sitting in the hot bath after the heat was cut has gone on cooking, and it reaches the pass tight and split however well it looked when it went in.

Where it goes wrong The bath was pushed too hot and allowed to boil, usually an outer vessel set over direct heat that was never turned down, or a bath topped up part way through with boiling water, so the mixture against the wall of the dish ran past 85C (185F) and its protein seized and squeezed out its liquid. The outer band is pitted and grainy, a ring of watery liquid weeps into the dish as soon as it is cut, and the centre is still slack, because the outside was overcooked long before the middle set.