DR RICHARD VOLZ (Plant & Food Research)
Acidity measurements are important along with soluble solids concentration and sweetness because combined with sweetness it gives an overall measure of the taste of that fruit, so its the balance of sweetness and acidity that we are interested in looking at for any one particular apple. Acidity measurements are carried out on juice samples. Here what we have to do is realise that in apple, the major acid is maelic acid and so therefore we can use a titration technique to assess the acid concentration in apple fruit. The concentration is quite a bit lower than say soluble solids concentration so here we have to use a relatively large amount of juice and the way we get that is juice an apple in a conventional juicer. Essentially what we do is we take a base solution and we put that into our unknown juice sample, or unknown acid juice sample and we neutralise that acid according to the amount of base that goes into that solution. We know the concentration of the amount of base going in, we know the volume of juice sample, therefore we can get the concentration of that acid in that juice sample.