A year ago I made my first Carolina-style BBQ sauce (specifically a Piedmont-style sauce). It was perfect, exactly what I was looking for in every way. I've never been able to replicate it.
The first batch was made with whatever red-cider vinegar we had in the cupboard; I didn't take notice of the brand, but I believe it was a supermarket generic brand, possibly either Giant or Harris-Teeter. The second batch I made was very, very harsh, and through trial and error I determined that it was the brand of vinegar that I used (Heinz red cider vinegar). The next batch was made with red wine vinegar and it was much better, but still not as good as the first batch (I still have a tiny bit of the first batch left). My latest batch is even better still, using the Giant-brand red cider vinegar -- but it's still not as good as that first batch.
I don't have words for why the first batch is better, other than "less harsh". Logically I know that vinegars can vary tremendously, and if I use a store brand, that will likely vary even more from batch to batch than a name brand; how can I make something that consistently excels if I can't define what I'm looking for?
My husband jokingly told me to find someone with a mass spectrometer, but I'm seriously considering it. Is there a better way? How do I go about figuring out what is different about that first batch? My supply is rapidly dwindling, just a few tablespoons, now.