When the bottom of your sourdough burns while the top remains unburnt, it means that the bottom of the loaf is being heated at a faster rate than the top of the loaf, which could be due to loading the loaf closer to the bottom heating element and baking on a high thermal conductivity material.
6 Tips to prevent the bottom of your sourdough from burning
1. Placing the loaf on a higher shelf in the oven
Most ovens are lined with heating elements on the top and bottom of the enclosure. If the loaf is placed off centre and too close to either the top or bottom of the oven, the loaf will be heated more rapidly on the side that is closer to the heating element and get burnt.
When your sourdough burns on the bottom while the top remains fine, check to see if the loaf is placed closer to the bottom of the oven, and if it is, try baking your sourdough on a higher shelf, closer to the centre.
2. Placing a heat insulator between the bottom heating element and your loaf
When baking multiple loafs in an oven, sometimes we have no choice but to load certain loafs in the oven off centred. The loaf that is placed closer to the bottom will have a burnt bottom while the top remains fine.
In this case, try placing a heat insulator between the bottom loaf and the bottom heating element, which will absorb the direct strong heat from the bottom heating element, promoting an even heat distribution throughout the loaf and preventing the bottom from burning.
A good heat insulator or barrier that could be used is any material with thermal heat conductivity of more than 1.0 W/m.K; pyrex, baking stone, baking tray, tiles, a cut out piece of aluminium foil all works fine. We do not want a material that has too little thermal conductivity as it can prevent so much heat from reaching the bottom of the loaf such that the bottom comes out the oven with a pale coloration.
Thermal conductivity of a material describes how fast the material absorbs and radiates heat from and to its surroundings; the higher the thermal conductivity of a material, the faster it absorbs and radiates heat from and to its surroundings.
This heat insulator should not touch your loaf, otherwise it may not work as intended and your loaf ends up burning on the bottom all the same.
3. Bake the loaf on a material of lower thermal conductivity
The material that we use to bake our loaf on plays a crucial role in how quickly the bottom of your loaf gets heated up. The higher the thermal conductivity of the material, the more likely is the bottom of your loaf to get burnt.
The recommended choice for baking surface is a baking stone because it has the ideal thermal conductivity that allows the bottom of the loaf to heat up quickly enough that it develops a golden brown crust, while at the same time not heating it up fast enough that the bottom of the loaf gets burnt.
Here are some other common material choices that bakers use as a baking surface. Try using a baking surface made of a material of lower thermal conductivity if the bottom of your sourdough is burning.
From the table below we can see that pyrex and baking stone has the lowest thermal conductivity while metallic materials has the highest thermal conductivity.
| Baking Surface Material | Thermal Conductivity (W/m.K) |
| Pyrex | 1.1 |
| Baking Stone | 1.5 |
| Ceramic | 2.5 |
| Cast Iron | 48 |
| Steel | 54 |
| Aluminium | 205 |
4. Reduce baking surface temperature by misting
If you have no choice but to bake with a baking surface of very high thermal conductivity such as those made of metals (cast iron, steel and aluminium), then try misting the baking surface with water once the oven is preheated and right before you load the loaf into the oven.
The water will evaporate and lower the temperature of your baking surface which will slow down the rise in temperature at the bottom of your loaf, reducing the chances of it getting burnt.
5. Bake without convection
Different convection oven makers has different air flow designs; some ovens channel their airflow from the bottom to the top which means that the hottest air makes contact with the bottom of the loaf first, heating the bottom of the loaf much quicker than the top of the loaf. This causes the bottom of the loaf to burn.
Baking with convection allows food to cook faster and saves energy. If you would still like to bake using convection, then try placing a heat barrier between the bottom of the oven and your baking surface. The heat barrier will absorb the hottest heat coming from the bottom of the oven.
Similar to point number 2, you can use a baking tray, a cut out piece of aluminium foil, a baking stone or any material that has a thermal conductivity of more than 1.0 W/m.K.
6. Use baking paper instead of oiling the pan
When baking sourdough of high hydration, it tends to stick to the baking surface and we sometimes use oil to prevent it from sticking. However, oil has a very high thermal conductivity, which heats up the bottom of the loaf at a much faster rate which can lead to it getting burnt.
A workaround is to use baking sheets or parchment paper rather than oiling the pan; it works the same but without increasing the thermal conductivity of the loaf, reducing its risk of burning.
