The question is the topic, but I'm looking to find out how to avoid overdoing it on the adjuncts. According to Papazian, no more than 20% should be used (when using 2-row, anyway). I recently used 2.5g of chocolate in a stout, and while I think it'll be fine, I want to know how to figure out the exact amount I CAN add.
Thanks for any help!
Trying to figure out an exact amount IMO would be difficult as there are many factors that ultimately go into the ferment ability of any given grain and specialty malts simply based on their processing prove more difficult to determine.
When I create a recipe I try to think about the final product and what it brings to the table, then work backwards. I start with the base to determine starting gravity and then add in small amounts of specialty grains based on what characteristics they bring to the beer. Color, aroma, complexity, head retention, etc. I find less is more in most cases. Then figure out mash temps, overall body of the beer, yeast strain , etc.
This all comes with experience and tweaking recipes all the time to fine tune a given recipe. I'd like to think I nail things on the first try but rarely is that the case, there is usually something to improve.
It's always easier to add a bit of something than try to figure out how much to remove. Designing Great Beers is a great reference for learning recipes and ingredients as it provides many guidleines and percentages of grain types used in all styles of beer. You will find most have 2-5% given for any specialty grain, very rarely much more than that.
Long winded and not really answering your question but hopefully it helps:)