So the birch sap is flowing and things are going great. I dug a new pit stove for boiling the sap, and I made the vertical hole about 3 feet deep and flared it out at the bottom with a hoe. It it about a foot in diameter. I dug the diagonal tunnel so that it intersected the vertical hole about 8 inches above the bottom, so that the wood fed through would go directly into the flames, not the bottom of the coals. I also used a 6" diameter piece of stovepipe to line the diagonal with, thanks for the idea Tel, it worked great! This stove cranks the heat out bigtime! I was able to throw all kinds of green and wet wood in there, a bunch of black locust bark, and the incredibly high heat easily burned everything. I was given a 55 gallon stainless steel barrel that I cut in half, which I use for boiling sap over the pit stove. It tolerates the heat wonderfully, and the sap boils vigorously from twigs if that's what I feed it.
I was able to make some birch beer and some birch syrup so far. For the beer, I boiled 20 gallons of sap down to 4, while adding barley, malt extract, hops, and yeast. For the last 25 minutes of this boil, I added about 3 gallons of sweet birch bark, which carries the strong essence of wintergreen. Filtered it and it is now fermenting! I also made a tea from the red inner bark, just as described in "Stalking the Wild Asparagus" by Eulle Gibbons. It was delicious, and I felt like it was the spring tonic he described it as.
The syrup was quite the treat. I started with 23 gallons of sweet birch sap in the barrel. I ended up boiling this down to just about a pint of syrup, knowing when to stop boiling with the use of a refractometer. This took way longer than it should have, because I was cautious not to burn the sugars by too vigorous of a boil. I learned through this process that this risk is only present during the very final stages of the boil. I was boiling from noon till 3 a.m. Next time, I will feed the pit stove so that it roars and roars, and I'm sure I can cut the time way down. The syrup is amazing to taste, I've had it in coffee, on waffles, on ice cream, and I love it!
To conclude, I think the pit stove is the perfect way to boil sap for small scale sugaring operations. You can get extreme heat, a clean burn, use any old wood scraps lying around, and do it in bad weather if needed. The Bengali pit stove is a great way to do any kind of cooking as well. Thanks again to the authors of "Rocket Mass Heaters", Ianto Evans and Leslie Jackson. Here are a couple pics: