I stumbled upon Black Blood of the earth (BBoTE) recently, and was intrigued, so I made up my own method for producing similar coffee, with spectacular results.

This is a modified cold extraction.

The reason for the cold extraction process (besides concentrating the caffeine greatly) as you may already know, is that you end up with a very low acidity coffee--meaning it won't stain your teeth, and it will be gentler on your stomach. Incidentally, the flavor is much altered as well. I find it is much more sweet and nutty than conventionally brewed coffee, which is easily burned, and contains the more bitter, acidic volatile oils that require heat to extract (you should never brew coffee at more than 204 f, or 96C. Optimal range for that method, 197-204F or 92-96F). The extended steep time gets more of the flavorful oils and caffeine. This also really lets you taste the beans. I have found the differences in the roast and type of bean is much more pronounced when coffee is prepared like this.

I used 12 oz of medium/coarse ground beans and roughly 1.2L of water, and a tablespoon of lecithin
(an emulsifier with almost no flavor, but I believe it helps extract some of the sweet/caramel and nutty flavored oils from the beans. Could be wrong, I havent tried this method without the Lecithin at the temp. range I have been using for this, but that being the only uncontrolled variable, I do have reason to believe this. It does aid in the extraction of oils and lipid soluble compounds into water. Lecithin is completely natural, occurring in egg yolks, and commercially available in a soy-derived form. Another reason I like the Lecithin is that it aids in forming a foam, (in molecular gastronomy this is one of its main uses), so you can whip a crema onto your iced espresso!)

I started with warm (not hot) water, and left this all over night at room temp (roughly 15 hrs. Aim for 12-20 hrs). In the morning, I used my french press to get as much water out of the beans as possible. Don't be surprised when that is only 50-70% at this point.
Next, I thoroughly mixed in about 200ml of water into the beans, and extracted as much water as possible again. I repeated this step two more times. I extracted the replaced-water-turned-coffee using the following method.

I continued squeezing with a great deal of pressure (I am 25, 6'3", 200lbs and athletic, so when I say a great deal, I mean a great deal.) holding the french press upside down. My fp is metal, and I only stopped short of breaking the plunger. I held it like this until it stopped dripping, which took some time. 12 oz of ground coffee occupies about 650ml. This step may be more easily done by wringing the grounds, small batch by small batch, through cheesecloth or a t shirt. I used this step as a replacement for the vacuum chamber segment of the BBoTE process.

The above step is important (to my budget). There is much valuable (and very concentrated) coffee left in the beans, and this lets you get at most of it. If you can afford the waste, the first pressing is the strongest possible caffeinated substance you can make. Drink it with caution. After the change in color of what your getting out becomes noticeable, you are done. It will be very noticeable. The first concentrate is thick and black, like crude oil. You will notice quickly that by the second or third pressing, the drip-stream allows light penetration, and the liquid (if in a separate receptacle from the initial pressing) is not so deeply opaque. If you keep these separate, the first extraction will be noticeably stronger. I combine them. It is all strong enough that it still averages out to much stronger than what youre used to.

I added my secondary extraction to my thick, tarry black coffee, adding up to ~1400ml, and ran it all through a metal filter for good measure, in case I missed some sediment (and I did), and Voi La!

This yielded a highly concentrated coffee that has a ridiculous kick. I'd estimate that it is on the order of 25-30 more caffeine/volume than a standard brewing. It is too strong to drink in this form, so I add water (you could use cream or milk, but i prefer my coffee black) at a ratio of about 3 pt coffee concentrate, 5 pt water, but this could be adjusted to taste. 1:1 would probably resemble strong espresso. I normally have 1600 ml of coffee before 2pm (my mug is an 800ml graduated pyrex beaker, if youve noticed the precision of my measurements). I drank 400ml of this, diluted to taste, and it took me until 4pm to finish. I have never FELT caffeine like I do with this. (im considering purchasing a vacuum chamber to evaporate the water, yielding a purer concentrate I could carry in a dropper to add to water anywhere I go...I know, Im a little eccentric, but hey, that's probably why I shave with something called a cutthroat.)