Hi,
I'm neither a programmer nor a recipe expert (sadly). What I can say though is that if its feasible something like this could be magnificent!!
Firstly, you could start from the important bit (what you want) and get suggestions of how to get there. Rather than having to work almost backwards, trying to sort through what does what until you think you've found the right combinations. Obviously great for the beginner, but even for the experts amongst us it could possibly throw up useful ideas at times.
Secondly it would be great to learn from, just change sliders to see what different recipe components and quantities contribute to the outcome. The action (slider) to result (recipe) feedback loop would be an excellent tool for immediately showing recipe/beer relationships.
I also think it could be invaluable in brining together the recipe expertise on this site into a single point of access. There's so much info on here that I must admit I can sometimes find it challenging to find even the more fundamental stuff I'm looking for. Stickies are fine but you can only have so many of them before you'd need a separate place for the info - sort of like a reference area, or something like this software idea which could almost be seen as a very focussed/clever search engine. Of course live recipe creation would be perfect, but even if it just returned links to suitable beer recipies (according to the slider settings) that would be great.
Fab Idea!!
(sorry I can't actually help much in achieving it though...

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