Why was my pie filling runny when warm but firm when cool

July 6, 2009 11:39 AM

Why was my peach pie filling runny when warm but firm when cool?

I made my first pie over the weekend. I used cornstarch as the thickening agent for the peach filling. I finished baking the pie about two hours before serving, and it was still a bit warm when I cut into it. After removing a piece or two, the vacant pie pan space filled up with filling, which was pretty runny-looking. So I made a mental note for next time to use more cornstarch or try tapioca. However, later on I noticed that the pie filling seemed pretty firm, as if it solidified as it cooled. But cornstarch thickens when heated, right? So why was my pie filling runny when warm but firm when cool?

posted by crLLC to food & drink (6 answers total)

The sugars and fats in the pie tighten when cooled.
posted by bitdamaged at 11:42 AM on July 6, 2009

Cornstarch isn't the only thickening agent present in your pie; peaches also contain pectin, which (I think) gels when cooled.
posted by saladin at 11:45 AM on July 6, 2009 [1 favorite]

Cornstarch thickens when heated and then sets as it cools. It would probably not have set so well without the pectin, which is why some other fruits are kind of a beast to pie-ify predictably, but what happened was in fact the expected behavior.
posted by Lyn Never at 11:57 AM on July 6, 2009

peaches also contain pectin, which (I think) gels when cooled.

You think correctly. Pectin does indeed gel when cooled (that's why and how jam and jelly become jam and jelly.
posted by EmpressCallipygos at 12:24 PM on July 6, 2009

Looks like pectin is my answer. For what it's worth, Wikipedia confirms that "[t]o prepare a pectin-gel, the ingredients are heated, dissolving the pectin. Upon cooling below gelling temperature, a gel starts to form." Also, this blog explains that high pectin fruits will result in thicker fillings. Thanks!
posted by crLLC at 2:49 PM on July 6, 2009

Most thickened pie fillings will be runnier when warm and thicken up when they cool. Note to my 17-year-old self making Thanksgiving dessert: lemon meringue pie is lemon meringue soup-in-a-crust if you're too impatient.

Tasted good, though.
posted by Lexica at 8:15 PM on July 6, 2009