Guest Post by Jonathan Thomas
This article is a collection of Facebook posts written by Jonathan Thomas on the Bread Made Easy Facebook group. I have collected them together here as I think they make interesting reading. You can pop over to the Facebook group to read the comments of others and to add your own or add a comment to this post.
How Much Does it Cost to Cook a Loaf of Bread ?
With the rocketing price of energy, I wanted to get a better grasp of how much money does it cost to cook a loaf of bread. I have estimated this using my smart-meter & the current energy tariff from my supplier, British Gas (which is 28.455 pence per kiloWatt-hour (kWh) ). I have an electric range cooker (“Rangemaster Toledo”) with a fan-assisted oven. Results may vary for a gas cooker, or a convection electric oven.
My standard method to make bread is to pre-heat a cast-iron “Dutch oven” inside my fan oven for 45 minutes at maximum temperature (250 deg C). I then start cooking the bread for an initial 25 minutes at maximum temperature with the Dutch oven lid on. The final stage is a further 20 minutes cooking with the Dutch oven lid removed & the fan oven temperature reduced to 220 deg C.
Here are the results:
Stage 1 – Preheating the oven – 1.37 kWh energy consumed
Stage 2 – 25 min bake at 250 degC with Dutch oven lid on – 0.68 kWh
Stage 3 – 20 min bake at 220 degC with Dutch oven lid off – 0.47 kWh
TOTAL Energy Required = 2.52 kWh £0.71 at my current tariff)
So it currently costs about 70 pence to cook a loaf of bread in my electric fan oven. It is interesting that over half the energy (1.37 kWh out of a total of 2.52 kWh) is needed to pre-heat the oven. This is not too surprising as a good oven with low heat leakage will keep a set temperature quite efficiently without much energy input. It is getting to the set temperature that requires a lot of energy.
To help improve my oven efficiency (by reducing unwanted heat leakage) I have recently replaced both the oven door catch (which was sticking) and the oven door rubber seal. A poorly fitting oven door can be a major source of heat leakage.
Part 2 – Baking without Pre-Heating the Oven
Following my previous post, I have baked another loaf with a baking schedule which excludes the initial pre-heating of the oven. The revised baking schedule is a straight one hour bake in my electric fan oven set at 240 deg C (thanks to Kath for suggesting this schedule). I measured the energy consumption every 10 minutes & these are the results:
Baking Time Electricity Used Cumulative Cost (for my BG Tariff)
0 min 0.00 kWh. £0.00
10 min 0.47 kWh £0.13
20 min 0.92 kWh £0.26
30 min 1.25 kWh £0.36
40 min 1.53 kWh £0.44
50 min 1.80 kWh. £0.51
60 min 2.06 kWh. £0.59
So the total baking energy cost, excluding the oven pre-heating stage, is about 60 pence, compared to 70 pence when pre-heating is included (see previous post).
It might seem odd that the cost difference is so modest when the pre-heating method has half the total cooking time with no bread in the oven! The explanation is that most of the energy consumed by the oven during baking is used in getting the oven to the required baking temperature. When the oven reaches the desired temperature the energy usage to keep it there drops substantially (by about half in my oven).
My loaf rise was much reduced with no pre-heating. I use a heavy cast iron Dutch oven to enclose the bread during baking & I suspect that using a cold cast iron Dutch oven retards the baking process & interferes with the initial “oven spring”. So I will be sticking with pre-heating my oven before baking, even though it costs 10 pence extra.
Part 3 – Pre-Heating the Oven when using a “Dutch Oven”
In the final part of this series I look at oven Pre-Heating in more detail. If we cut out this stage to save costs during baking, how does it impact the overall baking process. This is particularly important for those of us who use a Dutch oven to help our home ovens more closely mimic a steamy bread oven.
Please note that I use a fan-assisted electric oven & this will behave differently to both a conventional convection electric oven, or a indeed gas oven..
I looked at how quickly the baking zone of the oven warmed up when the oven thermostat was set to max (about 250 deg C for my oven). The baking zone is either the middle shelf of the oven, or inside the “Dutch oven” when a Dutch oven is used. I used an accurate digital thermometer to measure temperature with the temperature probe placed on a piece of baking parchment (to avoid direct contact between the temperature probe and the metal of the oven shelf, or the metal walls of Dutch oven, which could lead to erroneous results).
I have two Dutch Ovens of similar size. One is made of aluminium & weighs about 3 kg & the other is a fairly hefty cast iron casserole dish which weighs over 9 kg.
The results are shown in the graph below:
The graphs show that missing out the oven pre-heating stage when baking bread only has a minor effect when no Dutch oven is used. The temperature in the centre of the oven rises rapidly & is at optimum baking temperature in 10-15 minutes (see grey line on the graph).
However, when a Dutch oven is used the temperature rise is much, much slower. 15 minutes after setting the oven dial to 250 deg C, the actual temperature inside the aluminium Dutch oven is only 150 deg C (see red line on graph), whereas the cast iron Dutch oven has barely reached 100 deg C, less than half of the optimum baking temperature (blue line on graph) ! What is happening is that most of the heating energy of the oven is being used to heat up the large metal mass of the Dutch oven & is not getting to the dough. This helps explain why I had such a poor bread rise when I tried to cook bread in my cast iron Dutch oven when omitting the oven pre-heating stage.
My recommendation* from these tests is that oven pre-heating is not necessary when using an electric fan oven to cook bread if you are not using the Dutch oven method. If, however, you are using the Dutch oven method to better mimic a professional bread oven then I think that the pre-heating of the Dutch oven is an important step to achieve an optimal bake.
*Kath’s note – My experiments with baking with a cold dutch oven have led to different results to Jonathan’s. I have found that the cold start can lead to greater oven spring as the loaf reaches full proof as the oven heats up. You can watch my video here. The difference might be down to Jonathan using spelt flour in his loaves. Spelt has a different gliadin/glutenin ratio than wheat flour and this can lead to it being quicker to overproof. The cold start method may be leading to the spelt loaf over proofing as the oven heats up and collapsing a little, reducing the height of the final loaf.
A cheaper way to bake a loaf is to use your slow cooker. You can get the recipe and method here.
