Excerpts explaning how food shaders were appraoched in Ratatoille:

Quote - We also often used procedural and tiling textures over custom-painted textures per model. This allowed us to create interesting and complex patterns quickly, for reuse via slim (material editing app).

On shading grapes: > Quote - Techniques, such as paint integrated with procedural shading and painted vertex varying data to control subsurface contribution, helped provide additional control in the shaders.

If your local bookstore has a copy of the Renderman Shading Language Guide, flip to page 362. Also Check out Procedural Modeling And Texturing.