Why You Should Avoid Adding Regular Sugar To Iced Coffee
One of the benefits that iced coffee has over hot coffee is the taste, but that's not the case if you forget to add sugar (per Solis). While it sounds like a minor oversight, the corrective solution is not simply adding sugar to iced coffee. Why? Because it's ineffective and does not sweeten your coffee. Let's look at the science of it: There is less energy in the molecules of cold liquids, detracting from their ability to erode soluble additives, like grains of sugar (per Science Focus).
In terms of cold coffee, the sugar will partially dissolve at best, while a fair amount of it will settle at the bottom of the glass after stirring. The residual sugar granules will remain present, irrespective of how long you whisk the cup, as proven in an experiment at the Open Computer Facility at Berkley. The result will be bitter-tasting coffee with additional sugar calories (per Business Insider).
Why only add sugar to hot coffee
If you enjoy the crunchy texture of undissolved sugar in your iced coffee, then, by all means, add sugar to your cold coffee. The alternative for a perfect iced coffee, according to the blog Hello Little Home, is to add the sugar to hot coffee before you let it cool. We use hot water because warmer liquids are best for dissolving sugar. In the case of hot coffee (or water), the heated water molecules are charged with energy and rub up against the sugar granules faster and at a higher frequency, consequently eroding them to a point where they blend into the liquid better, per the Virginia Department Of Education.
If you miss your opportunity, a rescue for bitter iced coffee is to dissolve sugar in water separately. You can do this with a bit of water in a small saucepan brought up to heat over the stove. The resulting mixture can go into your iced coffee once the sugar is fully dissolved, per The Commons Cafe. This will allow the sugar to properly break down and actually sweeten your beverage.