Updating SQL Server Database
Use an indexed view instead:

CREATE VIEW AfricanRatingsAVG
WITH SCHEMABINDING
AS
SELECT RecipeID,
       COUNT_BIG(*) AS cnt,
       AVG(Rating) as rating
FROM   dbo.AfricanRatings
GROUP  BY RecipeID;
GO

CREATE UNIQUE CLUSTERED INDEX cdxAfricanRatingsAVG on AfricanRatingsAVG(RecipeID);


The engine will maintain the cnt and avg for you. Use the NOEXPAND hint when querying the view: 


  When NOEXPAND is specified for a view, the query optimizer considers
  using any indexes defined on the view.