The Absolute Best Way To Ensure Rhubarb Cake Doesn't Get Soggy - Tasting Table
Briefly

To prevent a soggy rhubarb cake, place the rhubarb on top of the batter rather than stirring it through, allowing moisture to escape.
Rhubarb releases a significant amount of moisture when heated; if incorporated into the batter, it can lead to gummy pockets.
Using a thicker cake batter can support the weight of the rhubarb, preventing it from sinking and allowing moisture to evaporate effectively.
The combination of tart rhubarb with sweet cake creates a delightful contrast, enhancing the overall flavor profile.
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