How do I get caramels to turn out grainy? Yes, I know the opposite of the usual question.  I've been making candy since I was a little kid. My caramels are always smooth and creamy.  My partner's father thinks they taste good but that the texture is all wrong.  He liked the gritty/grainy ones his mother used to make. Everything I have ever seen listed as a way to fix grainy caramels I have tried reversing.

I have tried many things, including:


adding granulated sugar late in the process
not using corn syrup or other invert sugar
cooking them at high temps
cooking them for too short a time
stirring or not stirring at all the wrong times
switching recipes
varying the fat content


I guess I am wondering what makes caramels turn out grainy.  It's not as far as I can tell, wholly related to the sugar dissolving/melting.  If it was adding some granulated sugar as it cools should cause more crystals to form. 

Is it related to the liquid content? Because sometimes after months in a cupboard even ordinarily smooth caramels will have developed some graininess.
As you mentioned it is all about how the crystals form. 

Some of the factors off the top of my head:


How saturated is the solution -
The more sugar packed into the syrup the more easily it will crystallize.
How quickly it cools -
The slower the bigger the crystals
Interference - 
Do you have a starch or other sugar molecules gumming up the works?


Obviously you already knew this from your question. 

Not using other sugars will help.
You might also try adding more sugar to the recipe at the beginning to fully saturate your solution. The fact that you add sugar at the end and it still dissolves in makes me think your solution could take a bit more. Letting the solution cool slowly with your seed sugar at the end should help.

You would think it would be easier to get it wrong. Perhaps you simply have too much experience doing it right.

Ask an amateur to try out your recipe and see if they fail properly.