Why can’t you make toasted bread and crisp dosas in your microwave oven?

Have you ever wondered how a dosa become crisp or how a bread toast is made brown and crisp? Of course, to do any of the above no knowledge of chemistry is required. But a man named Louis-Camille Maillard in the early 20th century decided to investigate. What he discovered is so fascinating that the complex chemical reaction is now called the Maillard Reaction. In normal english, it is called browning. Heat is the key to producing the Maillard Reaction and the resultant torrent of appetizing flavors and aromas. Through this reaction hundreds of new flovor compounds are produced which give the distinctive brown color and taste of the toasts, dosas, roasted meat etc. You can read the Wikipedia page on Maillard Reaction to see how complex it is. The reason I got interested is because I read somewhere that Microwave ovens can’t produce the Maillard Reaction. These days Corning does sell a browner/crisper aid for the microwave. I have tried using this aid and it does do a reasonably good job but not as good as a gas stove. But why is it that something as modern as the microwave oven can’t produce something a common fire or a gas stove or a electric stove can produce? If someone knows the answer please comment.


  1. Anonymous said July 18, 2007, 9:38 pm:

    Is it because the heat transfer in a microwave oven is by convection (or radiation) but by conduction in a normal tawa or a toaster? I guess the “pressure” also has got a role in making them crispier.

  2. Anonymous said July 19, 2007, 2:59 pm:

    Good point Mahesh. Conduction in the tawa or toaster must be a key point. Need to understand why that makes such a big difference? – Sukumar

  3. Anonymous said July 20, 2007, 12:44 am:

    To quote from the wikipedia link:

    “High temperature, high relative humidity, and alkaline conditions all promote the Maillard reaction.[3]

    The rate of Maillard reactions increases as the water activity increases, reaching a maximum at water activities in the range of 0.6 to 0.7. However, as the Maillard reaction produces water, further increases in water activity may inhibit Maillard reactions.[4]”

    This makes me think of one more thing! When we microwave, unlike cooking in a Tawa, further water activity chances are lesser since water would escape into the atmosphere. Whether that would happen so effectively in a closed microwaving condition?! This is just a random take from the information given there. – Ravi

  4. Anonymous said July 20, 2007, 1:51 am:

    Interesting point Ravi. Water is another key factor definitely.

  5. Anonymous said July 20, 2007, 3:37 am:

    AFAIK, when water gets heated in a microwave oven, it just gets into an excited state and not actually vaporise as opposed to conventional boiling. The water content in the dosa batter may not actually vaporise and let it harden.

    Thats why one has to be very cautious while removing boiled water out of the oven. Or normally people are advised to insert a blunt metal spoon or something to absorb the energy. Am I right??

  6. Anonymous said July 20, 2007, 3:53 am:

    Another interesting point Mahesh. I need to understand some more about microwave ovens and the heating process they use before i comment on this. I have also collected some more ideas around this topic. I will do another post after i am comfortable with the details.

  7. Anonymous said September 24, 2007, 3:47 pm:

    A microwave can heat liquid water past its normal boiling point, but without letting it boil off. On the stove that does not happen: The heat is extreme on the bottom, the water can’t help forming steam bubbles, and then they come upward, collecting more steam out of the water and keeping the whole just at the boiling temperature. In a microwave you can get a lot of water just past the boiling point, but no steam bubbles breaking loose … until you take it out and put something in it. Then all of a sudden you’ve got sites for a bubble to stick to while it grows. If there are a lot of them, like if you add finely powdered sweetener, all of those bubbles can shoot off at once and spray boiling water on you.