Yes to everything Charles said- whenever I weigh low-fat cocoa powders, I end up with a dry, overly-intense cake. Cocoa beans have a naturally-occurring cocoa butter content, so that the higher quality brands contain 20-24% cocoa butter. But many of the lower-priced cocoas have part of that removed, and are only about 10% cocoa butter.
Sometimes it is hard to tell from the nutritional label just how low-fat the cocoa is, but a quick call or email to the company will get you the fat content per 100 grams. If it’s below 20%, it will cause problems in recipes that were developed with full-fat cocoas.
The following are full-fat (20% or more) cocoas:
Green & Black’s
E. Guittard Cocoa Rouge
Valrona (this one has a burnt straw component to the flavor that I don’t care for, but some people love it)
The following are low-fat (10% or less) cocoas:
Hershey Special Dark
There must be other brands in both categories, but these are the ones I have baked with and confirmed cocoa butter content with the companies.
The best solution to this problem is to correct the cocoa butter content. I do it by using a combination of 25% by weight unsweetened chocolate (I like Scharffenberger) and 75% low-fat cocoa. For example, if a recipe calls for 100g of cocoa, I use 25g of unsweetened chocolate and 75g of low-fat cocoa. You can do a similar substitution with pure cocoa butter, but I find the unsweetened chocolate more available.
I chop the chocolate and add it to the boiling water along with the cocoa in recipes that use the hot water blooming technique. For recipes that just add the cocoa to the flour, you could either grate the chocolate very finely, or just measure the cocoa by volume and skip the correction to the fat content (this is what is recommended in the Sweeter Side of Amy’s Bread).
OK, I’ll get down off my soapbox now.