Chocolate – Homemade chocolate turns crumbly

I had to do some reading on this one. There are a lot of answers.

1- You should find a better recipe. Chocolate spread recipes I have used come in one of two styles.

The water in your recipe seems to be a problem. The nutella style that uses fat, sugar, and chocolate. These will not really dry out. Sometimes the oil will separate a little and will need to be mixed back in. I would group frostings in this group although, of course, they contain far more sugar.
See this recipe:
http://www.foodnetwork.com/recipes/gale-gand/chocolate-hazelnut-spread-with-crepes-recipe/index.html

Thick chocolate candy. AKA fudge. These contain water but the sugar and water are cooked together into a syrup so the water is not able to immediately dry out. They will crystallize if they are badly handled- many recipes contain a little corn syrup to prevent this. This does not seem to be what you are trying to make.

2- Store your concoction in a lidded container that isn't too much larger than your sauce. I use mason jars to store mine. Alternatively you can push plastic wrap down onto the surface of the spread.

3- Refrigeration. Recipes that don't contain dairy don't need to be refrigerated and in fact shouldn't be because it causes them to harden.

4- Adding water to melted chocolate is only a problem when dealing with chocolate that is dry and meant to solidify such as a molded chocolate. In such a case even a drop of water will cause seizing. In this case where there is already quite a bit of water in the recipe seizing is not a risk and you shouldn't have any problem mixing a tiny bit back in. Do not add water to the nutella-like spread recipes. They do not contain water and it will not mix in.

I can't tell from your description what is causing your sauce to harden- it could be drying out, separating, or crystallizing. Any of these will be solved by reheating and thoroughly stirring. Although water could be added to restore dried syrup I think you will get better results by switching to a recipe that uses fat in place of the water.

When making chocolate the cocoa beans are fermented, roasted, and crushed/ground. They are then sent through huge presses that separate the cocoa butter from the cocoa powder.

Chocolate is cocoa butter that has been emulsified with varying quantities of powder and usually a ton of sugar and sometimes milk. The rolling of the chocolate with the butter to enhance the texture is called conching.

Cocoa powder will dissolve in liquid if you mix it into enough sugar beforehand- this is how chocolate drink mixes are made.

Additionally chocolate is smooth and creamy because of the unique properties of cocoa butter. It can be tempered to form crystals that are solid at room temperature but melt at body temperature. This makes them smooth and melt in your mouth.

Another reason, besides unwholesome quantities of sugar, why cocoa powder is more harsh tasting than chocolate, is that chocolate has often been dutch processed where cocoa powder often hasn't.

Cocoa is naturally acidic and harsh tasting. Adding some alkalinity to balance its pH makes it much softer tasting- and darker in color.

You can buy dutch processed cocoa powder. Remember that some recipes need to be altered to use it- for example if the recipe called for baking soda you would have to use baking powder instead to maintain the correct pH.