I want to make a coffee cream filling for a mocha roll cake. If I dissolve instant coffee into heavy cream will it cause cream to not whip up properly?
You should be fine, but you may have difficulties dissolving the instant coffee in cold cream.
Let me suggest a tiny tweak:
Dissolve the instant coffee in a tablespoon or two of boiling water, let it cool until at least room temperature (or even refrigerator temperature) and add it to your semi-whipped cream.
If you use a cream with a sufficiently high fat content - 35% or even 40% - the additional water will not cause any problems with whipping the cream properly. The lower the fat content of your cream or cream-and-other-liquid-mix, the harder it is to whip. Try to stay above 30% and chill your cream and the bowl well. Your heavy cream should be absolutely fine.
You'll DEFINITELY be fine without any pre-mixing at all... I've done it and the coffee cream is great !!
Whipping cream is 60+% water, remember ? There is plenty enough water in the cream alone to dissolve the instant coffee granules...
Whether whipping cream whips up well has more to do with temperature and apparatus, and how much solids are in there... than how many percent fat... As long as it's sold as "whipping cream" it has enough fat to whip up...
Just to allay your fears, Stephie... adding 1 tablespoon of additional water to 1 cup of whipping cream is highly marginal... It's too little to materially affect the fat-water ratio enough to mess up the whipping... just that it's unnecessary...
I use this ratio from Rose Levy Beranbaum :
1 cup whipping cream
2 tablespoons sugar 1 teaspoon instant coffee granules
To the above you can also sprinkle in 1 tablespoon of Dutch-processed cocoa before you whip away... to get a mocha cream, which also tastes delish !!