Here is a material breakdown of the grapes material I made in Maya for Arnold. This is a direct tribute to the amazing artist Farid Ghanbari who inspired me to make this scene. He did the very same breakdown but for VRay, this is for Arnold: hopefully it can save you some time as I had to go with a lot of trial and error!
Included are some screens of the overall attributes for the Ai Skin material as well as noise and cloud maps I used respectively for the weight and roughness of the specular.
Here is my original artwork: https://www.artstation.com/artwork/r4kDm
And here is Farid Ghanbari VRay breakdown! https://www.artstation.com/artwork/1GZqL