Berries in cheesecake -> gray spots?
I will sometimes make a berry cheesecake by simmering fresh berries with sugar/cornstarch (raspberries, blueberries) or baking prior to pureeing (strawberries) and then combining the berry mixture with the cheesecake batter.
The flavor is quite nice, but I've noticed that after a day or two, grayish spots start to appear on the top of the cheesecake. Is this some type of oxidation, and if so, is the source the berry skin or seeds? Can this be prevented or mitigated somehow?
I can't speak to the issue of the other berries, but blueberries turn dairy produces a grey color when the two are combined. I have read that colonialists boiled blueberries in milk to make grey paint. Nevertheless, i suspect it's a chemical reaction between the dairy in the cheesecake and the juices of the berries. You might try sprinkling the berries with flour before introducing them to the cheese cake and see if that helps.
Agreed, it is a chemical reaction - not pretty, but harmless. Some pigments turn blue or grey in alkaline solutions, but I've always associated it with recipes with eggs, which are fairly neutral, so maybe it is not the pH but the combination of the pigments with egg yolks pigments. And not all red fruits have the same pigment or react the same. I find cooked strawberries stay red, but raspberries can turn something a really gross color grey pretty quickly.
You could serve the berries as a compote on the side, or add a little gelatin and spread them on top of the baked cheesecake for a top layer. You might still get some color change where the layers meet, but maybe not as bad.
Thanks, everyone, for the input - I will experiment with both acidic and alkaline solutions and report back!
Hi all, sorry it took so long to reply, but I wanted to perform a couple of experiments. It seems that increasing the acidity helps the most, but I think it only delays whatever the reaction is.
I added lemon juice and it helped with the strawberries, but the raspberries still developed the spots relatively quickly.
Going with a more brute force method, I added baking soda and cream of tartar to two separate cheesecakes. The cream of tartar worked well and the baking soda actually seemed to cause it to color faster! So I'm guessing acidity is the answer, but it only mitigates the problem.