At first create a empty string as shown below
Hello Jeff,
While saving the Drink Object retrieve the IntegrentsSelect list by association and create a variable Integredients and iterate the list and add the Attribute in Integredients variable with comma separated and finally set the Variable in Integredients attribute in Drink object using change object and commit.
Your data-definition is very unlike the normal datastructure for this kind of setup. Usually it look like this:
But you probably have a usecase for it. Maybe for a drink 'Coffee', you can select from IngredientsSelect "sugar", "sugar and milk", "cinnamon and milk" and "milk". And for a drink 'Tea' you can select only "sugar", "sugar and milk".
The answer of Dhinesh gets you your multiple attributes in one attribute. All I have to add to that answer is:
But in your usecase I would advise to use an entity storing those ingredient combinations: