I have recently started enjoying cold brew (over ice) in the afternoons. In the morning I still like my coffee hot. Is there a preferred or recommended method for heating? What factors should I take into account? I have tried adding hot water, but it makes the coffee too weak before I am able to get the temperature up where I want. Microwaving seems to negatively affect the taste.
The best result I got was warming up in a bain-marie. No science here---just my trials... I believe for now that bain-marie preserves more flavours and "respects" the aromas.
Heating cold-brew coffee was surprising to me the first time. Such unexplored flavours with the exact same beans I use for drip, etc. I hope you'll enjoy, and explore for more questions here!
I used to work at Starbucks, and a coworker there described a process she had learned at a previous coffee shop where they heated cold press using the steam wand on the espresso machine. We tried it, and I found it lost much of its character and became more noticeably bitter, but then again the blend we used for our cold press at Starbucks was too bright and astringent for my tastes to begin with. Your mileage may vary, and a fuller-bodied coffee with "sweeter" flavor notes like cocoa or berry might resist this tendency toward bitterness a bit better.
The downside is that this requires a steam wand, which many people don't have at home. But it introduces less water into the coffee than simply adding hot water to cold press, and could give you more precise temperature control, so if you have the equipment, it couldn't hurt to try.
If you want to test it without investing in equipment, you could ask a local coffee shop that sells cold press if this is something they could make for you.