A Foolproof Rhubarb Pie That Won’t Turn to Soup, Thanks to a Genius Trick

Sweet, tart, and jammy, strawberry rhubarb pie is the quintessential spring dessert. Come spring and early summer, I scour the farmers’ market for those bright crimson rhubarb stalks, ready to load the trunk of my car with as much as I can fit. Rhubarb season is fleeting—and the only acceptable move is to take full advantage of the moment by buying pounds and pounds of it to turn it into crisps, pickles, compotes, and, of course, pie. 

In theory, making a strawberry rhubarb pie is easy. You chop up your fruit (though I should point out that rhubarb is technically a vegetable), toss it with sugar and your thickener of choice, encase it in pie dough, and bake until bubbling and golden brown.

The only problem? Strawberries and rhubarb both have low pectin levels and a lot of moisture—a recipe for a watery, mushy mess, especially if you don’t use the right kind and amount of thickener. There are also questions of how best to handle the fillings. What’s the best size to cut the strawberry and rhubarb? Do they need to be macerated first to draw out moisture? What additional flavorings are good? And what’s an ideal ratio of strawberries to rhubarb? 

In my attempt to nail down the perfect strawberry rhubarb pie, I baked a dozen, and did further experiments that zeroed in on some of the filling variables until I came up with my ideal version. I’m talking about a pie that balances the sweetness of strawberries with the tanginess of rhubarb, with a just-set, slightly saucy texture of softened fruit that still holds some of its shape.

The only problem? Strawberries and rhubarb both have low pectin levels and a lot of moisture—a recipe for a watery, mushy mess, especially if you don’t use the right kind and amount of thickener. There are also questions of how best to handle the fillings. What’s the best size to cut the strawberry and rhubarb? Do they need to be macerated first to draw out moisture? What additional flavorings are good? And what’s an ideal ratio of strawberries to rhubarb? 

In my attempt to nail down the perfect strawberry rhubarb pie, I baked a dozen, and did further experiments that zeroed in on some of the filling variables until I came up with my ideal version. I’m talking about a pie that balances the sweetness of strawberries with the tanginess of rhubarb, with a just-set, slightly saucy texture of softened fruit that still holds some of its shape.

The Right Ratio of Fruit and Dicing Decisions

Because I wanted a flavorful pie that allowed both the strawberries and rhubarb to shine, I started with a 1:1 ratio by weight of strawberries to rhubarb, both finely diced. What I didn’t realize was just how much water the strawberries would contribute to the pie filling. Even with an adequate amount of thickener, the pies made with equal parts strawberries and rhubarb were invariably too loose. You might wonder, why not just use more thickener? We could, but simply increasing starch until the liquid is thick enough solves one problem while creating another: Stabilizing excess liquid with even more starch results in a stretchy, slimy filling that—while certainly thicker—is not appealing. 

With this in mind, I adjusted the ratios to reduce water from the strawberries, opting for two parts rhubarb to one part strawberries. Instead of a fine dice—which I suspect exposed a little too much surface area that allowed more water to leach out and created a runny filling—I opted for 1/2-inch pieces. This was the ideal size of fruit: large enough for the pieces to remain distinct, but small enough to soften and cook down into a slightly jammy filling. 

While this fixed the texture problem, it threw off the flavor balance. I wanted the pie to taste distinctly like a combination of strawberries and rhubarb, but now it was too rhubarb-forward. To make up for the decrease in fresh strawberries, I folded in a few tablespoons of strawberry jam, which helped intensify the berry flavor without contributing any additional water.

Preventing a Runny Filling: What Kind and How Much Thickener Should You Use?

Look at most fruit pie recipes, and you’ll see that they typically call for all-purpose flour, cornstarch, potato starch, or tapioca starch as a thickener. This is because most fruit used in pie fillings (think berries, stone fruit, or apples) hold plenty of water that’s released during the cooking process. Without a thickener, you’d end up with a runny pie—but there’s only so much a thickening agent can do to help you achieve a just-set filling that’s neither soup nor sludge.

The best pies—which have a bright freshness and a jammy texture—depend on proper moisture management, which can be achieved multiple ways. My testing already addressed the ratio of strawberries to rhubarb and how large to dice them, but I was simultaneously tinkering with other variables to zero in on my ideal flavor and texture. One of those variables: the type and quantity of thickener. As I wrote above, more thickener doesn’t solve all problems. In order to get my filling to work, I had to not only switch up the ratio of fruit but also experiment with different thickeners and methods of incorporating them.

I started using tapioca starch, former Serious Eats editor Stella Parks’ preferred pie thickener, which sets fruit fillings without becoming overly gloppy. I used 5.5% of the total weight of fruit, Stella’s recommended amount of starch. But even after reducing the amount of fresh strawberries in my filling, it still wasn’t enough to absorb the amount of liquid they unleashed. When I increased the amount of starch to 6%, the filling managed to somehow be both too loose and too gelatinous, underscoring the point that simply adding more thickener wasn’t going to be the sole solution to the problem.

The Foolproof Way for Thickening Strawberry Rhubarb Pie

When I first published this recipe in 2023, I called for minute, or quick-cooking, tapioca pearl fragments. Finely ground minute tapioca resulted in a pie filling that was just set and jammy enough to slightly ooze out of the pie when cut into. Several readers, however, mentioned that the tapioca never fully dissolved in their pie and resulted in jelly-like blobs. With this in mind, I went back to the kitchen and began experimenting again.

I ultimately landed on a much simpler method: I macerate the strawberries and rhubarb to draw out excess liquid and concentrate the strawberry and rhubarb’s flavors, then briefly cook it on the stove. I toss the fruit in cornstarch and pectin, reincorporate several tablespoons of the macerating liquid to hydrate the starches, then bring it to a simmer to help it gelatinize. The pectin is crucial here because strawberries and rhubarb both have low quantities of pectin, a naturally occurring polysaccharide and fiber that helps set pies and fillings, the addition of several tablespoons helps encourage the filling here to set. 

It’s a similar method to how some savory pies, including chicken pot pie and shepherd’s pie, are made. You sauté the aromatics and meat, coat it in several tablespoons of flour, and then deglaze with a liquid like water or broth. Ultimately, this version is much simpler and more straightforward—and it results in a just-set pie with no jelly-like blobs in sight.

May 2023

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