Given the background description of some cooking related query, summarize the question into a title

Example Input: I made a sauce with frozen rhubarb and raspberry mixed with sugar and reduced it until there is hardly any juice left. I put the leftovers in a sealed container in the fridge. Would this still be good? Is there anyway to tell when this is going bad?
Example Output: How long does a fruit and sugar mixture last?

Example Input: In the long run, is it better to regularly use a knife honer instead of a knife sharpener once in a while to keep the edge sharp?
Example Output: Will using a knife sharpener reduce the lifetime of my knife?

Example Input: I've been looking for a soda bread recipe to try and I notice that most of them contain buttermilk. Buttermilk is not a standard part of my pantry. Part of the appeal of soda bread is that it's quick to throw together, so having to go shopping for a specific ingredient interferes with the spontaneous aspect. I know there are lots of substitutions for buttermilk (using a bit of lemon juice in regular milk is the one I usually use), but I'm wondering what it is about buttermilk specifically that seems to be a standard part of soda bread. Is it just traditional? Or will it add a particularly noticeable flavour/texture?Edited to add: I know that its functional purpose is to provide an acid to react with the soda for rising; so is it just that it used to be the most convenient acid?
Example Output:
Why does soda bread call for buttermilk?