I would like to concentrate flavour by reducing the water content but I do not wish to alter the temperature of the liquid. Is there a way to reduce the water content without boiling? Apart from waiting days for evaporation?
It's not necessarily a practical home kitchen answer, but rotary evaporators do this, by lowering the pressure over the liquid and circulating the liquid to increase surface area.
There does exist a culinary vacuum rotary evaporator, for only $9,999.95 by special order! Note that it also captures the vapor to condense, because often the flavor you want is actually volatile aromatic compounds, which evaporate faster than the water does, so trying to evaporate/boil away water is futile.
So if what you want to concentrate is aromatic, you're probably out of luck for home purposes. If you just want something non-aromatic dissolved in the water (dumb example: reducing sugar water into syrup) then boiling/evaporation can work, though. You could certainly speed things along by using as broad a surface as possible (a large pan), gently heating, and blowing a fan over the surface. But it's still going to take an awfully long time without actually boiling.
You could put the container of food into a bigger closed container also containing a strong desiccant like zeolithe or silica gel - these will probably needed to be dried in a hot oven before use, but that has nothing to do with heating or not heating the food. Make sure the desiccant is kept from contacting the food directly. The desiccant will constantly strive to dry the air in the container, whilst the food will try to do the opposite and thus lose moisture...
that's an interesting idea! Do you have any estimation for the time saved by this process vs leaving the stuff in a standard room atmosphere?– rumtscho ♦Jan 7, 2016 at 11:49
No... but since this is a commonly advised method in chemistry texts, that is probably where to look for estimates... Jan 7, 2016 at 12:21
Ah, I was hoping for an entertaining anecdote of homegrown kitchen science.– rumtscho ♦Jan 7, 2016 at 12:42
There are some dishwashers on the market that use zeolite to dry the dishes, so use near food-contacting items to draw away water is not unheard of... Jan 7, 2016 at 13:08
There are no practical ways to do it quickly and without heating.
If you want to go with room temperature dehydration, agitation will help. There are products meant to stir food for you (I used to have a nice one by some British startup, it ran off 4 AA batteries), or you could use a stand mixer. When you use a very slow setting, the temperature rise through friction will be negligible.
Combine that with a large surface and a chamber of very dry air as suggested by rackandboneman for even quicker evaporation. This should shorten the process significantly. But it will still be a "set it up and come after a long time" thing, not a "cook it up quickly" thing. And you'll probably be within the danger zone for any usable amount of food, so you should only use it with shelf stable liquids, unless you can afford to set a refrigerator aside for the process.
I do not wish to alter the temperature of the liquid... just leaving it out will cause it to move toward the ambient temperature of the room. Are really wanting to 'not alter' or just 'not boil'?