Making Better Toasts in Home Toaster Ovens
Here are some things you can do to make better toasts in your toaster oven at home:
If you slice your own bread, give some thought to the appropriate thickness. If the slice is too thick, there is a danger that the interior is not warm while the surface is burned.
If you use a toaster oven and don’t like the browning pattern on your toast, experiment with different positions inside the oven.
Humidity inside the toaster oven has some effect on the internal temperature of the bread. As the surface of the bread dries out, the moisture inside starts to migrate out and takes energy away, effectively cooling down the interior of the bread. The speed at which water evaporates is determined by the relative humidity of the oven air. You could put a bowl of boiled water inside the oven as a crude way to control the humidity, but I don’t see much of a difference in my own experiments. I suspect in the short time the toast is made, it’s more effective to control the heat input to the bread.
Ideas for a Better Toaster Oven
A conventional toaster oven controls two things in the toasting process: output power and timing. They actually don’t seem to exercise much control over the output power, other than ramping it up as quickly as possible. This will get us warm bread with a somewhat unpredictable crust, but to get what we want (an even golden crust with a soft interior), we need to have better control of the surface temperature of, and the heat dumped into, the bread.
The first thing to fix is that we cannot operate in an open loop. Every piece of bread is different, and every person’s idea of doneness level number 4 is different. Some sensors to collect information about the bread and the heating processes could be:
Infrared thermometer: To measure the surface temperature of the bread. To minimize error caused by reflection from the bread surface, the heating element of the oven should be turned off (or blocked) during the temperature measurement.
Camera: To take pictures and determine the color of the crust. Users should be able to choose the shade of brown they desire in the final product, instead of an arbitrary number of doneness. To get controlled color measurement, the oven should not have a glass window, which leaks heat and causes cold spots inside the oven anyway.
Scale and shape sensor: The shape sensor could work with radar or structured light. With the weight and density of the bread, we can simulate how much heat input will bring the bread to the desired temperature. With knowledge of the shape and location of the bread, we can calculate the irradiation that actually arrives at the bread, instead of the radiation leaving the heating element.
Heat flux sensor: It would be good to know how much heat actually goes into the bread. It’s probably impractical to get an accurate overall number, but data from a sample area could help.
Moisture meter: The moisture, surface temperature, and weight change over time will give us a better idea of the true state of the bread.
To fully take advantage of these data, we need more precise and flexible control:
The heating control should support multi-step, multi-level programs. The heating process should support a specific temperature profile over time, just like a reflow oven for PCB assembly. For instance, maybe the best way to make toast is to bring up the overall temperature of the bread slices before browning the surface, as in the reverse sear of steaks.
In general, the penetration depth of infrared radiation varies with the wavelength and the moisture content of the bread. It would be desirable to be able to control the radiation spectrum of the heating element over time.
To support the above two control characteristics, the heating elements should have low latency.
The heating on either side of the bread should be controlled separately. We don’t always want the two sides to heat up the same way.
The heating should have a finer spatial resolution so we can adapt to and remedy uneven browning.
Finally, to tie everything together, we need to have good simulation models. It’s probably better to host them in the cloud so an improved model can be easily deployed. To that end, the oven needs a wireless data link. It solves another problem: I really don’t want to put a big display on the oven. It feels like a mockery of the concept of smart appliances. Now, those pictures captured by the camera can be sent to any of the myriad screens we already have in the house.