I want to make Nigella's Chocolate Lime Cake from Kitchen but over the summer I started using limes for the first time and I am now noticing that the limes I am buying have a different fragrance and flavour. The ones I purchased over the summer months have an almost coconutty flavour and scent along with the acid edge. My most recent purchases taste very much like an unripe lemon. Does the flavour depend on the variety of lime I buy, and is there a way to tell the difference? Which should I use for the cake? I am in Victoria, Australia, in case that has any bearing. Thank you all very much for your help.
The type of lime most frequently found in supermarkets across the world is the Persian lime (somethimes called Tahitian lime). It has few seeds and as it ripens it will turn from green to yellow. A riper lime will be less acidic in flavour.
The other type of lime sometimes sold is a Key lime. These are most commonly found in the US. They are smaller than a Persian lime (about the size of a walnut in its shell), have more seeds and have a strong, acidic flavour. They usually have very thin skins. Their strong flavour makes them very popular for Key Lime Pie.
It could be that the flavour profile of your limes is changing as you move from riper to less ripe limes (maybe as a new season comes in) or you are now buying the more acidic key limes. It is difficult to tell without a fuller description of the limes.
Nigella's Flourless Chocolate Lime Cake is made with Persian limes (fairly green ones, not yellow) as these are the ones you can buy in the UK. A lot of the lime flavour in the cake comes from the lime zest, so the larger type of Persian lime is preferred and the quantity of lime juice is based from a Persian lime. If you can only find Key limes then these will still work, though you may need to use two of them to get enough zest. A Persian lime yields approximately 2 tablespoons of lime juice though you may want to use sligtly less Key lime juice as it is stronger in flavour.