This calculator produces necessary measurements to produce a baked custard in the style of key lime pie BUT using any fruit juice. The starting parameters are scaled for a 9 inch diameter pie. You can adjust to create multiple pies, different sizes, or even a square/rectangular baking vessel. The ingredients provided are only for the filling. You will have to adapt the recipe and scale for the crust, as there are too many variables.

Input the percentage of sugar and percentage of titratable acidity for the fruit juice you are using. Sugar can be measured directly as Brix with a refractometer, referenced from a nutritional label (if using store-bought juice), or researched online for an estimate.

Titratable acidity will likely need to be researched for the specific fruit juice you are using. YOU CANNOT use a pH meter. If you have a large enough quantity of juice, you can also determine the titratable acidity experimentally. Using Dave's technique with a precision scale and baking soda. See video >

If you research the overall acidity for the juice you are using, you may also see the quantity of specific acids. You can optionally input the ratio of citric and malic acid. (For example, orange juice is almost entirely citric acid, apples or cherries are primarily malic acid, and grapefruit is a specific ratio of both.) You can leave the first toggle in the default position if composition is unknown, and it will still turn out great.

The following output is all measurements in grams. The succinic acid solution is optional but highly recommended, and that specific measurement can be converted to milliliters. Do so if that is the method that gives you the best precision. The first set of ingredients are used to create the modified juice. You will then use all or a majority of this solution for the final custard.

The final key input is the Calibration. Sweetened condensed milk is very sticky, so you may not get everything out of the can. If you are scaling the recipe, you may also be just over requiring a whole number of cans. Calibration requires you to input the actual yield of condensed milk. If you are short, you make up any missing quantity with additional dairy and sugar. Or you can choose to scale the recipe down slightly, to utilize just your yield. Just beware that the 2nd option result in a slightly narrower depth for the actual custard.