Speed when reducing sherry
I found a bottle of sherry and thought it had a strong fig taste so I tried reducing it with maple syrup. In practice this meant I just brought it to a boil uncovered and waited until maybe a quarter was left. It ended up being tart and somewhat darkly fruity with a maple sweetness. Not terrible for a first attempt at using it, but this made me wonder: what is the difference between reducing this by boiling and reducing it by a long, slow simmer? I don't imagine they're equivalent. My instinct is that gentler heat better preserves nuances of flavor but I'm really just guessing.
am unclear why you added the maple syrup?
reductions most typically are done at a hard boil.
not sure how your sherry tasted "before" you found it, but the flavor of fig would not be unusual in a bottle that is perfectly sound. sherry is already oxidized, so won't go bad on the shelf. the flavor will fade, but the stuff doesn't go "off".
I wanted the flavor of maple syrup and was also unsure if sherry would thicken without it. But to be honest I'm not sure how well that maple flavor survived.
The source of some confusion may be that I'm comparing this to say a reduction of balsamic vinegar (or any gastrique I guess). Many instructions say to reduce balsamic vinegar slowly over low heat for an hour or two, and it only ever thickens because it's got sugar in it naturally. By comparison the one time I tried reducing apple cider vinegar it just simmered away into nothing instead of thickening because the sugar content is too low. Similarly I thought sherry would have so little natural sugar that it would just reduce to nothing rather than thicken, so I added maple syrup. Is this incorrect?
That is not really true. Most Chef's want reductions done over a low heat.I was trained to reduces sauces slowly. Sauces that are reduced very quickly tent to be weaker on flavor and complexity. We did side by sides when I was Apprenticing and it was apparent which Sauce had been reduced more quickly