As a general rule of thumb, you should avoid burning your toast, says Sonpal. Beyond its unpleasant, bitter flavor, burnt toast, “there are many health issues related to burnt bread.”

Cording explains, “When foods are heated to high temperatures, a potentially carcinogenic compound called acrylamide forms from the starches and amino acids (arginine) present in food.” If your bread is lightly toasted, that’s totally fine, “but if you get any char on there, there’s more of a chance that some acrylamide was formed,” she says.

https://www.mindbodygreen.com/articles/toasted-vs-untoasted-bread