I'm a bit confused about how to tell whether i have got the ratio right for my ganache when i first make it...as opposed to leaving it to set overnight and then trying to frost the cake (for under fondant) only to discover I made it too thick/thin.
I know that to ganache a cake i'm supposed to have 'peanut butter consistency' but presumably that's how it will be the next day after setting overnight? So what will that look like when I first make it? And will that correct consistency be just sitting at room temperature or do I need to reheat it before using it?
And if I got the consistency wrong, can I fix it then and use right away??
So many questions!! Until you can work out the correct ratio for where you live at different times of the year (different temperatures) you should always make it the day before and let is set overnight a room temperature. You will get to know what is the right ratio in summer and winter and in between.
When it is all melted it can be near impossible to tell the difference by the consistency. You can't really ice a cake with it like that anyway it would run off, but I am assuming you are letting it partially set and then icing the cake with it while still fairly soft and are hoping it will continue to set.
After the ganache has set over night at room temperature you can reheat slightly before using to make spreading easier.
I live in Sydney, Australia where the summer gets really hot. I made a wedding cake last weekend where it was 42 degrees celcius so I had to amend my ganache ratio's to allow for the heat. Generally speaking, dark chocolate will be a 2:1 ratio (2 parts chocolate, 1 part cream), white and milk chocolate will be 3:1. In really warm weather, just increase the amount of chocolate you put in (so dark chocolate can be 3:1 or 4:1 ratio) - that way it sets firmer and less chance on melting when on the cake.
When you make your ganache, it will be very liquid so hard to tell how it will set. But it shouldnt be oily or grainy & make sure all the lumps are melted otherwise it will remain lumpy after it's set. I make ganache in the evening & leave on the bench overnight to set. If it's too hard, zap in the microwave for 5-10sec bursts. Have a few practice go's - best of luck :)