One of the chief complaints Viennese bakers have about American Sacher tortes (and believe me, they have a lot of them) is that they lack the bitter tang of their Viennese cousins. This they usually attribute to the chocolate, since we here in America tend to prefer mellower-tasting chocolates than folks on the continent, or so it’s said. I’m not sure that’s true anymore, since everywhere you look now there are 60%, 70% and 80% bars and confections. You can eat yourself into cacao oblivion sampling chocolate at fancy food trade shows these days…which I can tell you from personal experience isn’t nearly as much fun as it sounds.
One way to get that extra bit of Euro bitterness into your Sacher torte (or any chocolate preparation, really), is coffee. Coffee is a very close relative of chocolate, flavor-wise, and a little of it can give you that bit of astringency that Europeans tend to favor. The trick is to only add a little, but make sure it’s strong. I have a can of espresso that I keep around for that purpose (mostly for flourless chocoalte cakes) so I can mix up a bit of concentrated brew if need be. Though I have to admit that not being a coffee (or espresso) drinker, it tends to lose its punch after a few weeks. A nice alternative that I discovered a couple of years ago are these little packets of Java Juice. They keep forever in the pantry and have far more coffee flavor than the typical “extracts” you find in stores.
But whichever route you decide to go, espresso or extract, all you need to do is sneak a tablespoon or so into your batter, and/or into your glaze mixture before you start heating it. It’s not traditional of course, but since when has that ever stopped me?