How long will Royal Icing store, safely, if put in an air tight container? I use the recipe with meringue powder, sugar and water. I made a batch on Feb 22. I saved it and need more next week, that will make it nearly 5 weeks old. It has been in an air tight container. I don't ever use much at a time so I hate to make a batch and then throw more than half of it away. Maybe I should make a smaller batch?! 
Not sure what the food-safe answer is. When I make it to teach my Wilton students, I usually save that batch and use it for the course. I know sugar acts as a preservative, but I am just not sure how long it will last.
Wilton tells you that it can be stored in an air tight container, unrefrigerated for 2 weeks - needing to be re-mixed prior to use. I read here on posts that it can be frozen for months - thawed and re-mixed. I didn't beleive it but I tried it and it worked fine. Hope that helps you. 
Five weeks is too long..Even after 5 days the consistency of your RI changes. It tends to melt more, Even though is still good in taste. The quality of some things will decrease. I use it for more for petunias and other details that dont need a stiffer consistency.
Hope this helps,
Edna 
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