echinosum writes
But adding
alkali to reduce acidity generally only works in very
specific ways in
cooking. The main alkali used in cooking is sodium
bicarbonate, which
will fizz, a technique used for raising cakes, but
probably not helpful
in fruit tart.

I used to use bicarb to rescue milk that was on the point of going off
(the state where it looked OK cold but separated as soon as it was
heated) if I wanted to cook with it, eg blancmange.

ISTR it used to be common practice to use it when boiling veg, to
preserve the colour, but the practice was strongly discouraged from the
60s on, on the grounds that it destroyed Vit C.
--
Kay