Pie Thickeners Compared: Cornstarch, Flour, Tapioca and More
Fruit gives off juice as it bakes, and something has to hold it. Here is how the common thickeners differ and how to choose.
A fruit pie with no thickener slides apart into soup when you cut it. Too much and the filling turns gluey. The thickener you pick changes how clear the juices look, how soft the filling feels, and whether the pie holds up in the freezer. None of the common choices is wrong, but each one suits some fruits better than others.
How thickeners work
Cornstarch, tapioca, arrowroot and the starch in flour all work the same way. The starch granules soak up hot juice, swell, and form a gel. That only happens once the filling is hot enough, which for most starches means a steady bubble in the center of the pie, not just at the edges. If you cut a pie that never bubbled, the starch hasn't finished its job, and the filling will run.
Cooling matters just as much. The gel keeps firming as the pie cools, so a fruit pie needs at least 3 to 4 hours on a rack before slicing. A warm slice of any fruit pie will be looser than the same pie later.
The main choices
Cornstarch is the most common. It is a strong thickener, flavorless, and easy to find. It makes a smooth, soft set with a slightly glossy look, though the juices can turn a little cloudy. Cornstarch can lose strength if it cooks for a long time in very acidic juice, and it can weep after freezing and thawing.
All-purpose flour is the old-fashioned standby, and most people already have it. It is a weaker thickener, so you need about twice as much as cornstarch. The juices come out opaque and a bit pasty, and a heavy hand can leave a faint raw-flour taste. It holds up fine in acidic fruit, which makes it a decent backup for tart pies.
Tapioca comes in two forms. Quick-cooking (instant) tapioca is small granules that you mix with the fruit and let sit for about 15 minutes so they soften. They bake into a clear, bright filling, but you may notice small, soft pearls in the finished pie. Tapioca starch (sometimes sold as tapioca flour) is a fine powder that behaves like cornstarch, gives very clear juices and a slightly stretchy, glossy texture, and freezes well.
Arrowroot is a fine starch from a tropical root. It gives clear, glossy juices and a clean flavor, and it is usually swapped for cornstarch one for one. It thickens at a lower temperature, but it can thin out again if the pie is baked a long time. It also tends to turn slimy with dairy, so it is best kept to fruit pies.
Clear Jel is a modified cornstarch sold online and in some baking and canning shops. Bakeries and home canners use it because it stays stable through long cooking, acid and freezing. If you make fruit pie filling to freeze or can, it is worth knowing about. Follow the package directions, since the cook and instant types are used differently.
Side-by-side comparison
| Thickener | Clarity | Texture | Acid | Freezing | Amount for a 9-inch pie (about 6 cups / 1.4 L fruit) |
|---|---|---|---|---|---|
| Cornstarch | Fairly clear, slightly cloudy | Soft, smooth | Weakens with long cooking in very tart fruit | Fair, may weep | 3 to 4 Tbsp (25 to 35 g) |
| All-purpose flour | Opaque | Soft, a little pasty | Handles acid well | Good | 6 to 8 Tbsp (50 to 65 g) |
| Quick-cooking tapioca | Very clear | Bright, with small soft pearls | Handles acid well | Good | 3 to 4 Tbsp (30 to 40 g) |
| Tapioca starch | Very clear, glossy | Smooth, slightly stretchy | Handles acid well | Good | 3 to 4 Tbsp (25 to 35 g) |
| Arrowroot | Very clear, glossy | Smooth, light | Fine, but can thin if over-baked | Good | 3 to 4 Tbsp (25 to 35 g) |
These are starting points, not exact rules. Juicy fruit like ripe peaches or berries sits at the high end. Firmer fruit, like apples, usually needs less.
Swapping one for another
A handy rule of thumb: 1 tablespoon of cornstarch does the work of about 2 tablespoons of flour. Arrowroot and tapioca starch can generally replace cornstarch tablespoon for tablespoon. Quick-cooking tapioca is a little less concentrated, so use roughly 1 1/2 to 2 tablespoons in place of each tablespoon of cornstarch, and let it rest with the fruit first.
Quick tips for a set filling
- Whisk the starch into the sugar first, then toss with the fruit. This keeps it from clumping.
- Bake on a lower rack, and look for thick bubbles in the center vents before you take the pie out.
- Let the pie cool for 3 to 4 hours before slicing.
- Do not add extra starch to fix a runny pie after the fact. Use it as a reason to bake a little longer next time.
Which thickener for which pie
Blueberry and other berry pies do well with cornstarch or tapioca starch, which keep the deep color from going muddy. Our blueberry pie guide covers the details for that fruit.
Peach pie releases a lot of juice. Cornstarch or quick-cooking tapioca both work, and tapioca keeps the filling bright. See the peach pie guide for more.
Cherry pie is tart and very juicy, so tapioca or Clear Jel gives a clear, shiny result that looks like cherries and not like paste.
Apple pie needs the least help. Apples hold their structure and contain natural pectin, so 2 to 3 tablespoons of flour or cornstarch is often plenty.
Strawberry-rhubarb pie is the watery one. Rhubarb is both acidic and full of liquid, so tapioca or flour stands up well. Tossing the cut fruit with sugar for 30 minutes and draining some of the juice helps too. See the strawberry-rhubarb pie guide.
If you plan to freeze
If you want to freeze an unbaked pie or a baked slice, tapioca starch, quick-cooking tapioca, flour or Clear Jel are the safest choices. Cornstarch fillings are more likely to weep a little when thawed. Freezing an unbaked pie and baking it straight from the freezer works well with any of these, as long as you add 15 to 20 minutes to the bake time.