Making royal icing today, for a rather overdue Christmas cake.
I always end up with too much icing sugar, based on my normal recipe which asks for 4 large egg whites and 500g icing sugar.
So today I used 3 egg whites and as much icing sugar as "felt right". Is this fair enough?
If it's taking a long time for stiff peaks to form, is this a sign of too little icing sugar? And if I overdid the icing sugar how would I tell?
The consistency of royal icing depends on many things, including the size of your eggs, but also the humidity/weather. So if you know what stiffness you want, it's perfectly valid to add sugar until it "feels right". (I usually make royal icing with meringue powder rather than fresh egg whites, which removes one variable from the equation [the size of the eggs], but I still have to adjust the sugar to get the right consistency.)
As far as troubleshooting, if you've been whipping away and it's still gloopy, by all means add more sugar. If you overdo the sugar, you'll know immediately: it'll be too stiff to mix. (In which case, depending on the quantities involved you can either just add a teaspoon of warm water, or you can whip up another egg white separately until soft peaks form, then fold it into your icing.)
I can't believe no one has said this. You liked your old "pre-modification" recipe, right? But you just want less of it? Your eggs are the same size as always?
3egg whites/4egg whites=X/500g icing sugar. Remember learning cross multiplication in school?
Assuming your eggs are the same size: if four egg whites marry well with 500 grams of sugar, then three egg whites will behave the same way with 375 grams of sugar.
To have a sense of accuracy:
Weigh 2 egg whites together - note that weight and then note that same weight divided by two.
Add a third egg white, weigh the total. Take the total weight of three egg whites, divide by three. That's an unnecessary step, but it will give you an even better idea of margin of error.
So the weight in grams of two egg whites divided by two should be about equal to the weight of three egg whites divided by three. Get it? If they're significantly different, take the average of three and run with that.
So now you know not only the total weight of your egg whites, but also the average weight of your egg whites. Knowing that average weight can allow accuracy regardless of the weight of future whites. Just replace #ofeggwhites with total-weight-of-egg-whites, so grams instead of #ofeggwhites.
So if you don't want to weigh your egg whites, you can at least estimate. (That is of course eliminating such things as weather from the equation, but it's a great place to start.)
