In some of our apple pies we find that the filling has turned blue
The blue discoloration in your apple pie filling is probably caused by a natural pigment. Natural pigments from blackcurrants, black grape skins and some flowers such as dahlias, lobelias and Michaelmas daisies contain anthocyanins. The most probable explanation of the coloration on your apple pie filling is that it has come from utensils or machinery that have previously been used for blackcurrant filling. If the same utensils are being employed for both types of filling, we suggest that you ensure complete removal of any traces of blackcurrant before the apple is applied.
Apples can turn pink if too high a temperature is used during baking. The pink discoloration is due to the hydrolysis of leucoanthocyanins present in the cell tissue of the apple. These normally colourless substances are closely related to the natural red or purple colours (anthocyanins) of fruit. The changes in the leucoanthocyanins to the coloured forms are accelerated by acidity, and the more acid apples appear to discolour more readily on heating than do less acid varieties. The apple most commonly grown in the UK for culinary purposes is the Bramley Seedling. It seldom develops a pink discoloration when canned as a solid pack apple processed at 100 °C (212 °F), but when used in apple pudding, special care has to be taken to keep the temperature below 110 °C (230 °F) to keep discoloration to a minimum.
To avoid discoloration in this case prepare a sugar/water/starch gel and allow it to cool before blending in the solid pack apples. It is inadvisable to add any extra acid to the filling.
See also 10.5.
Continue reading here: Can you suggest a solution to the problem of shrinkage in our apple pie filling
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