The phenomenon you're experiencing, where tomatoes seem to get hotter than everything else in your toasted sandwiches, can be attributed to several factors:
Moisture content: Tomatoes have a high water content compared to many other ingredients commonly used in toasted sandwiches. When heated, water takes longer to reach its boiling point, and the energy from the heat is primarily used to evaporate the water within the tomato. This can make the tomato feel hotter than other ingredients in the sandwich, which have a lower moisture content and can reach higher temperatures more quickly.
Thermal conductivity: The thermal conductivity of a material determines how quickly it can transfer heat. Metals, like the toaster's heating elements or the grill, have high thermal conductivity and can distribute heat relatively evenly across the sandwich. However, tomatoes have a lower thermal conductivity compared to metals, so the heat takes a bit longer to spread throughout the tomato, leading to the perception of higher heat in the part that is directly in contact with the hot surface.
Density and heat capacity: The density and heat capacity of a material also influence how it absorbs and retains heat. Tomatoes have a lower density and specific heat capacity compared to some other sandwich ingredients like meat or cheese. This means they require less energy to heat up, and they can also lose heat more quickly, leading to a sensation of higher temperature when you bite into the sandwich.
Perception of temperature: Our perception of temperature is not solely based on the actual temperature of the ingredients but is also influenced by other factors, such as the thermal conductivity and texture of the food. Tomatoes, being soft and juicy, can more effectively transfer their heat to your mouth, creating a sensation of greater heat compared to drier and less juicy ingredients.
To sum up, the higher moisture content, lower thermal conductivity, and different density and heat capacity of tomatoes compared to other sandwich ingredients contribute to the perception that they get hotter than everything else in your toasted sandwiches.