I made green tea muffins following the recipe here. I like my muffins moist and fluffy, so I added banana as suggested by the recipe and replaced half of the baking powder with baking soda. I also added a teaspoon of rice vinegar to activate the baking soda.

Right before baking the mix was vibrantly green, but after 13 minutes in the oven the muffins had turned very dark — and this morning they were even darker.

What happened, and how can I prevent it?


  • I'm just asking to be very sure: you didn't overbake or burn them and your oven temperature was correct? In that case, could you please post a picture of a cut open muffin?
    – Stephie
    Commented Mar 8, 2017 at 14:02
  • 1
    Banana bread often turns a dark brown, If you mix dark green and dark brown that is the color I'd expect to get.
    – GdD
    Commented Mar 8, 2017 at 16:14
  • @Stephie The oven temperature was fine, and the cake doesn't taste overcooked. I'll post a picture when I'm back home.
    – Clément
    Commented Mar 8, 2017 at 19:25
  • @GdD: Thanks — From the pictures in the recipe, though, I wasn't expecting this color. Is there a way to avoid it?
    – Clément
    Commented Mar 8, 2017 at 19:26
  • 1
    My recommendation would be to stick to the recipe @CFP, leave out the banana.
    – GdD
    Commented Mar 8, 2017 at 20:25

4 Answers 4


Your first step would be to stick to the recipe. pH changes are well known to interfere with plant pigments. Adding baking soda and vinegar can very well have interfered with something in the muffins, be it the tea or something else. I am not 100% sure this must have been it, but it is the likeliest reason.

Also, I would recommend against making changes to a recipe before you have tried it as-written. You cannot know how changes affect it, and what unintended consequences they have, until you have established a reference. For example, you cannot know if your addition of baking soda made the muffins both fluffier and darker, or if it only made them dark without any change in fluffiness.


Reviewing HaroldMcGee and thanks to rumtscho's test, it seems to be more complex than just changing the pH environment.

The culprit is still likely the banana content though. According to Harold McGee, high temperatures can result in the phenolic components of the banana to create a brown discolorization, even if the enzymes who are usually responsible for the browning process of bananas together with oxygen, are no longer active.

An acidic environment helps preventing this, so the high temperature + banana + not very acidic environment is a fair chance for the reason your muffins turned out so dark.

  • 1
    I was thinking along these lines, only the exact baking soda + anthocyanin combination sounds unlikely. Anthocyanins are mostly known for being between red and fuchsia (think beets) and turn dark blue in higher pH. That would be a highly uncommon banana cultivar. Also see ajcn.nutrition.org/content/93/4/865.full. To be sure, I now mashed some banana pulp with soda, and it is not displaying any darkening (it should be very quick when it is a pH-pigment reaction). So, I think your general direction is good, but the concrete suggestion is a bit off.
    – rumtscho
    Commented Mar 9, 2017 at 22:18
  • My excuse: I had no banana at home to test. :-) Commented Mar 10, 2017 at 19:21
  • I doubt that this is what happened. I tried the same recipe with no green tea, and the muffins were very pale. Adding lemon (so more acid) didn't make them paler, either, so I'd guess there's enough acid to prevent the banana from browning… unless green tea is basic?
    – Clément
    Commented Mar 15, 2017 at 4:28
  • I guess there is no other solution than making a batch with green tea and no banana and check the result. Green tea is known to have an anti-browning effect though, this seems strange. If only green tea + banana causes this, I guess we have to redirect the question to the chemistry guys. Commented Mar 17, 2017 at 9:16

If you take a look at the results of.. why does my tea turn dark dark darker when I add baking soda. The results indicate that the chemistry changes. Acids create lighter colors. Bases remove some acid ions and allow darker base ions to color the product. Use the baking powder and add a squish of lemon juice, the muffins should be lighter..

  • Please could you add a link for the change in colour of tea. Commented Jul 6, 2019 at 12:36

I blame the banana. Always blaming the banana. Bananas get black, they do.

Go again but this time sub in smashed canned pears and a spoon or 2 of mascarpone cheese instead of banana.

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