Is soy milk an acceptable substitute for whole milk in cooking and baking?
When we first tested subbing soy milk for regular whole milk in 2006, we determined that the sweetened kind that was most available at the time was fine for baking and desserts but created a cloying sweetness in savory applications like béchamel. Now that most brands of soy milk offer an unsweetened version of their product, we decided it was time to reevaluate.
We used unsweetened soy milk in yellow cake and vanilla cream pie filling as well as in fish chowder and béchamel. Tasters reported that the cake and pie filling were slightly less rich than the dairy versions in flavor and texture (not surprising, considering that sweetened or unsweetened soy milk contains half the fat of whole milk) but were still acceptable. As for béchamel, tasters declared it bland, watery, and unappealing, noting that there was little to distract from the soy flavor and the lack of dairy richness. In the more complex chowder, the soy flavor was less noticeable, but we needed to add twice as much thickener to achieve a consistency that was comparable to that of the sample made with regular milk. Also, soy milk can curdle if it gets too hot. To prevent this, add it off heat and then warm the soup gently just to serving temperature.
Our advice: Go ahead and use both sweetened and unsweetened soy milk in desserts. Unsweetened soy milk will work in savory dishes, as long as there is enough richness and complexity in the recipe to make up for its thin flavor and consistency.