Cold sourdough can be loaded straight into a hot oven, while still achieving excellent results as long as you add a few minutes to the baking time to ensure a full bake. The amount of rise of the sourdough is more important than its temperature, when deciding when to load the your dough into the hot oven.
Should you increase oven temperature to compensate for the cold sourdough?
You should not increase the oven temperature when baking a cold sourdough that has just been removed from the refrigerator. Increasing the oven temperature only speeds up the darkening of the crust, resulting in a burnt crust before your loaf can be fully cooked in the middle.
The hotter oven temperature warms up the surface of the dough quickly, while the heat from the oven takes a longer time to reach deep cold centre of your sourdough. As the cold centre of your loaf rises in temperature slowly, the resulting bake will have a burnt crust with a raw middle crumb.
Instead of increasing the oven temperature, it would be better to bake at the normal temperature of 232-240 Celcius, over a longer duration. A normal oven temperature darkens the crust at a slower rate, allowing enough time for the cold centre of your sourdough bread to be baked fully before the crust gets burnt.
How much longer should I bake my cold sourdough bread?
The changes in the duration of your bake depends on the weight and shape of your sourdough bread.
When baking a sourdough of a smaller weight (400g) and a long thin shape (baguette), the temperature of your sourdough does not matter as much, as the centre of the loaf is able to be heated up rather quickly and it is not necessary to increase your baking time to achieve a full bake.
A dough of a smaller weight has a larger surface area per given mass than a dough of a larger weight. A smaller dough exchanges heat with the environment more effectively than a larger dough due to the increase in surface area, hence a cold dough of a smaller weight rises in temperature much quicker.
Similarly, a dough of the same weight that has been formed into a long thin shape has more surface area than one that was formed into a round shape. The extra surface area allows heat to be exchanged more effectively with the environment, hence a cold long thin shaped dough rises in temperature much quicker than a dough formed into a round shape.
However, when baking a cold sourdough of a larger weight (more than 600g) and a round shape, there is less surface area where heat is exchanged and the centre of your dough takes a longer time to rise in temperature, hence it would be necessary to add 5-7 minutes to your total bake time.
The best way to determine if your sourdough bread has been fully baked is to use a digital thermometer to observe the internal temperature of your loaf; the sourdough bread is fully baked once the thermometer registers 88 Celcius.
The degree of rise is the most important factor in deciding when to load the dough into the oven
If we were to remove an already over risen cold sourdough from the refrigerator and wait for it to warm up to room temperature before loading it into the oven, the baked sourdough bread will most likely collapse and flatten out as it has gone past its peak rise.
To prevent a loaf from collapsing in the oven, we typically aim for 90% rise before the dough is loaded into the oven, so that it still has some room to grow and expand during oven spring. If we load the dough at full rise, or past full rise, the yeast and bacteria would have ran out of food to undergo fermentation, oven spring is limited, and the loaf collapses in the oven.
We cannot negate the effects of an over risen sourdough, but we can negate the effects of a cold sourdough by increasing the duration of the bake. Hence, it is more important to immediately load a cold and fully risen sourdough into the hot oven, to prevent it from collapsing and flattening out.
If your sourdough has gone past the point of 90% rise when it is removed from the refrigerator, do not bake with steam, as steaming an over risen dough will only increase the likeliness for the loaf to collapse.
Steaming lowers the surface temperature of dough which delays the formation of the hard crust. If we steam an already over risen dough, the dough would have collapsed before the hard crust can set to hold it in shape. Without steaming, the hard crust sets rapidly, providing structure to the over risen dough before it has the chance to collapse.