Which is the best mixer to use for large quantities of scone dough? I've researched Spiral mixers and they seem like the best option perhaps. I usually mix everything by hand but I'd like to scale my business and would like to make up to 12 batches at a time. Also with making larger quantities is there a formula that should be used to alter the rising agent, baking powder in particular? thx!
Based on my professional experience of making 2000 scones* a week for a bakery in Los Angeles:
If you're in North America, get a Hobart. They're quite expensive, so your best bet is to shop restaurant resales and auctions for a used one -- they're also very durable. If you're in another country, find your region's equivalent professional-bakery-grade mixer. A home-kitchen mixer won't last, and could easily die on you in a few months.
You do not want a spiral mixer. Spiral mixers are designed for kneading yeasted doughs with a lot of gluten development, like breads and pizza dough. With scones, you do not want gluten development. On the Hobart, you would use the "flat beater" mixer attachment, not the dough hook.
If you supply the details about actual batch size, I could even recommend a specific Hobart model.
(* this is the American definition of scones which is a large, sweetened shortbread, and not the British ones, which are more like what Americans call "biscuits" and not at all like what the British call "biscuits")