I stumbled on this thread looking for ideas. I know it's old, but figured I'd share what I know about chocolate from the perspective of a chocolate maker.
First, powder is created by grinding the nibs to chocolate liquor (think, unsweetened baking chocolate) then thrown into a hydraulic press to press the cocoa butter out. This process is not perfect and even under the best industrial conditions, you'll be leaving approximately 10% behind. Cocoa powder strives to be solely the cocoa solids, which give chocolate its flavor.
Cocoa nibs are generally created by cracking and winnowing cocoa beans. The cocoa beans have a paper thin husk that is very bitter and not good to eat. So after roasting (or skipping the roasting step for raw) the beans are cracked. The winnowing process is separating the cocoa nibs from the now free husk pieces, leaving you with just the cocoa bean pieces. These are generally approximately 50% cocoa butter by weight, which is why using nibs in brewing tends to be difficult at best; unless used during a boil where the cb can be melted
If you're trying to use cocoa nibs so you can control the aromatics and flavor profile of the chocolate, you will be best to roast the nibs and grind them into a thick paste. This can be very hard on most equipment. Best things I've seen that do this well is the Champion Juicer, or a wet grinder. If you have a peanut butter grinder, that will work as well. What happens here is the cocoa butter liquefies due to the friction created by the grinding and will give you a very coarse cocoa liquor. If you have the ability to, you can grind this down to refine further. While in a liquid state, you can attempt to mix this into hot water. Hot, but not boiling; just needs to keep the cocoa butter from solidifying. Once thoroughly mixed, the cocoa butter oils will likely rise to the surface and solidify.
Something to note about commercial cocoa powders; these generally are ok for baking, but not the best beans to use for cocoa flavor as they're the rejected beans (generally speaking) from chocolate production. Cocoa butter is needed in most cases, and would then be extracted from these reject beans so as to waste little to nothing. A premium producer may seek out and make a premium grade cocoa powder from normal grade beans, but in most cases these tend to have much higher fat contents sometimes 20% or more.
Boiling or getting hot water to mix cocoa powder or an unsweetened baking chocolate would be ideal. Cocoa solids because they are dried out, are quite hygroscopic, which is why it's sometimes difficult to fully soak the cocoa powder making it a messy endeavor. The solids will grab onto water and hold onto it, making a lot of the surrouding particles clump together. Breaking these clumps up, or breaking through so that the powder does more than just sit on top takes some coaxing and mixing to get done right.
Chocolate bars should only be used if you know and really trust the maker of the bars. Some premium bars can be had with 100% cocoa content (refined chocolate liquor) or 2-ingredient bars with just sugar and cocoa beans. All other ingredients that you'll want to watch for that can taint the mead or lend flavors you're not trying for include milk, butter, vanilla beans, emulsifiers (lecithin, pbpr, etc) and in some cases various spices. I almost forgot to mention, alkalizers. Dutch process cocoa powder and a lot of milk chocolates, and even some dark chocolates tend to be processed with alkalizers to neutralize the acids in the cocoa. Most commonly this is baking soda (sodium bicarbonate) Which may or may not be desired in your mead.
To figure out how much you would need, you need to keep in mind that ~50% of the nibs by weight are cocoa butter and ~10% of Hershey's natural cocoa powder is cocoa butter. So if a recipe such as the one posted earlier on this thread asks for 16oz of cocoa powder, you would need to count on needing 32oz of cocoa nibs or baking chocolate.
If you're using a chocolate bar, you should only be using a dark chocolate which will have a percentage rating. That percentage is the amount of cocoa product that's there. Because of the way labeling is, that does not mean that's the amount of cocoa solids, there can and usually is added cocoa butter to make the chocolate easier to work with. Some companies will tell you what that ratio is, some wont. Assuming it's a 2-ingredient bar, the remainder of the percentage is going to be sugar. So, using a finished chocolate bar is going to be more confusing and will be trial and error from manufacturer to manufacturer. But as a starting point, you'll again, need to at least double the cocoa solid content to what is called for in powder. So a 2oz bar that is 70% chocolate would require 22.85 bars or 48.7oz to approximate 16 oz of powder.
I'll likely be trying this using some fresh nibs, right out of the roaster and refined into a fine paste, then put into some hot water, where the chocolate liquor and water will make up the must. I'll keep you informed of how that goes if you're interested.
I hope this helps someone
