As a baker, my primary goals have long been purity of flavor and unadulterated texture. It all began over forty years ago, with apple pie. I despaired over all the juices that exuded during baking, rendering the bottom crust soggy and pointless. I saw recipes that suggested macerating the apple slices in sugar until they released some of their juices and then throwing out the juices.
But I couldn’t bear to discard all that flavorful sugared apple juice, so I reduced it, cooled it, and poured it back into the apple slices—and that is how the idea of concentrating the liquid was born.
When I wrote The Cake Bible thirty years ago, I included fruit purées like raspberry and strawberry. But berry purées presented new challenges. If you macerate berries in sugar then strain and reduce the juices, those juices will start to caramelize very quickly, as berries require a lot more sugar than something like apples or peaches to counter their natural bitterness. While caramelization enhances apple flavor, it would compromise the berry flavor. Plus, you never know how much purée you’ll get from seedy berries after you strain them, so it’s wise not to add sugar too early on—or you’ll risk overdoing it!
So I decided to coax juices from the berries without cooking them, by freezing and thawing instead. I strained the liquid released from the thawed berries, then reduced it to about one-quarter of the original, using a microwave oven on high power. Because the juices bubbled up during the early stages of microwaving, I coated the Pyrex measuring cup with nonstick cooking spray, which also made it easier to pour out the concentrated liquid later on.
I then puréed the thawed pulp, strained out the seeds, and, stirred this into the cooled concentrated juices along with sugar—usually equal to half the volume of the total mixture (that is, juices plus pulp). I used these purées as sauces, as add-ins to buttercreams, ganache, and whipped cream, and as swirls in cheesecake batter.
A pastry chef who worked at the restaurant Bouley told me that this technique of concentrating berry’s juices was the most important recipe in my entire book and changed the way he made fruit purées. And I was shocked and delighted to discover on a visit to London that chef Michael Aldridge at the renowned Connaught Hotel restaurant also used a microwave to accomplish the same task (it was rare indeed to find a microwave oven in a three-star restaurant!).
A few years later, when I was working at Procter and Gamble on a freelance project, Richard Walker, one of the engineers who became head of the Tropicana division, told me that it was essentially the same technique they used in concentrating orange juice! Both Michael and Richard agreed that microwave was ideal because it produced the most pure flavor—although, if one is dealing with a large amount of liquid in a home kitchen, it is advisable to use a cooktop to avoid frequently opening the microwave to stir.
Years later, when I spent a day at Michèl Cluizel’s chocolate factory in Normandy, I asked him to have ready frozen-and-thawed raspberries so that I could make him my raspberry sauce (yes, he had a microwave—but only in his laboratory, where the necessary glass containers were permissible). I was delighted when Monsieur Cluizel said that my raspberry sauce was much better than the raspberry sauce product his chef made.
I’ve now gone on to reduce all liquids (and drippings) that would benefit from concentration to intensify flavor, from the juices of roast chicken which I add to grains, to the juices of macerated fruit, which I pour back over the uncooked fruit. This technique also works perfectly with stone fruit, such as peaches and nectarines, when making pies or crisps. I like to add a little butter at the start of the cooking process and to concentrate the juices just to the point where they begin to caramelize. And because there is less liquid in the fruit filling, there is also less need for as much thickener so the purity of the flavor is enhanced even further.
When it comes to savory cooking, Robert L. Wolke, former food science columnist of the Washington Post, said it best when asked what to do with the concentrated brown drippings from roasts: “If you don’t know what to do with them you don’t deserve them—send them to me!”
Reducing fruit juices in a microwave requires a container at least four times larger than the volume of the fruit and is a little more time consuming than using a cooktop. It is important either to swirl or stir every 20 to 30 seconds to prevent air bubbles, which would cause the juices to explode out of the container and all over the microwave. Once this happens, you never again forget to stir!
Also, be sure to watch carefully toward the end of the reduction—it goes really quickly and could burn. I once went a little too far with maple syrup and it became too thick to pour. I stirred in some heavy cream, reheated it and lo’ and behold: maple caramel!
What fruits do you find most challenging to bake with? Tell us in the comments below.