The Oven and its Temperamental Temperature

So this week I have devised an experiment. We have a fan oven which means that the heat should be evenly distributed throughout the oven however, I've had my doubts about whether that really is the case. For example my mum has noticed that when we make pizzas and bake them in the oven the ones on the top shelf of the oven cook faster than the ones on a lower shelf. So I decided to investigate this using shortbread. I decided to use shortbread because it's quite simple to make but also it is also fairly universal; all the recipes use similar ingredients with similar methods. Therefore my conclusion is relevant for all shortbread baking. 

I used a BBC GoodFood recipe (find the recipe here) that seemed simple enough for me to recreate. Unfortunately I did not have rice flour so instead I used ciabatta flour, reassuring myself with the fact that it could not be a factor in deciding which batch tasted the best as they would all have the weird flour. I made a batch, divided the dough into equal portions and I baked each individually at a different shelf in the oven for the same length of time and at the same temperature. I decided to then feed my family one shortbread from each of the oven shelves (A, B and C) in a blind food test. I set up a questionnaire which asked the subject to note down which shortbread they thought tasted the best.

My hypothesis is that the top shelf shortbread will taste the best.

There were unfortunately many limitations with my experiment. Even though I used a ruler to measure the length and width of each shortbread, the thickness of each shortbread 'bite' was different as I didn't actively measure it. This was a mistake as the thickness makes a huge difference in the baking time which then affects the crumbliness and chewiness of the shortbread. This could definitely affect the popularity of the shortbreads.

Also I didn't have 3 trays that were exactly the same! 2 were the same but the third tray that I used was deeper and was a metallic silver colour which could have affected the baking of the shortbreads. Metallic silver colours are worse radiators whereas the black trays are good emitters of heat. This meant that the shortbreads were surrounded by completely different environments temperature wise without including the different shelves.  

The biscuits were not distributed evenly across the trays they were skewed over to a side and I think that the shortbreads on the far right and left baked faster than the middle shortbreads. This hypothesis requires further testing.

Sadly I could not put all the shortbread trays in at the same as I don't have 3 arms and I also couldn't remove all three trays at the same time so some trays were in the oven a fraction longer than others and unfortunately I didn't write down which these were or even coordinate the loading and removal of the trays to equalize the total times the trays spent in the oven.

My experiment was also on quite a small scale only 5 subjects took part and filled out the questionnaire after the tasting the shortbreads which means that the results I gathered weren't the most reliable.

However, even though we have established that it wasn't a fair test the results show that the top shelf in the oven produced the best tasting shortbread though the middle shelf was not far behind. This makes sense as shortbread should have a short and crumbly texture and the top of the oven is often the hottest. This is because when the air in the oven heats up the particles gain kinetic energy and therefore move faster and further apart which makes hot air less dense than less hot air so the hotter air rises. So it makes sense for the top shelf shortbread to be the crumbliest and yummiest shortbread.
Because the votes weren't very evenly spread across A,B and C this experiment suggests that there is a difference in temperature in ovens, even in very good fan ovens.

On to the results...

The graph below shows that the majority of people voted that the Top Shelf shortbread tasted the best followed extremely closely by the Middle Shelf shortbread. The interesting thing is that no one voted for the Bottom Shelf shortbread and this suggests that there was a difference in temperatures at the different levels in the oven as otherwise the votes would have been more or less evenly distributed across A, B and C.

Therefore, in conclusion the best oven shelf for baking shortbread is the top or middle one. However, keep an eye on them because they'll burn quicker at the top too! To achieve a more reliable conclusion this experiment should be repeated with more subjects and a greater effort to control more variables for example the thickness of each shortbread.