I use 8oz pureed cucumber in 3lb soap. I use it to replace 8oz of water. As long as the cucumber is finely pureed, there is no problem. Once I grated it instead of pureeing it and ended up with little rotten or rancid-looking spots in the final soap. I've also soaped carrots (babyfood), canteloupe, strawberry, kiwi, avocado successfully using the same process.