fermentation trouble in braggot

Are you sure that it is dead, really truly dead? It may simply be that it has settled down to a more reasonable fermentation rate after acting like Mt. Meadsuvius for the first few days. Have you tracked the SG over the course of several days and can you confirm that it has really stuck at 1.040?

Remember, CO2 bubbling through an airlock is not a reliable indicator of fermentation rate. Too many of those things, or their stoppers or O-rings, leak.

Yeah - this one does sound strange. In addition to warming it up a bit, also swirl the yeast lees back up into the must to see if you can kick-start any active cells that may have settled out.

One more pH related question - how are you doing the measurement? Strips, or a meter? If strips, what's their active range, how old are they, and can you test them with some standard solutions to see if they're giving you a correct reading? I've had problems with old pH strips misleading me in the past.

Lacking any definitive smoking gun, you can add yeast hulls when you rack which will pull out some yeast toxins from the must, assuming that is possibly the problem. Adding a source of amino nitrogen (such as Fermaid-O or 2133 or, lacking those, some Go-Ferm) might also help.

D47 doesn't like getting too cold, but you're not down where it can stall due to temperature (usually around 58-62F), so I'm stumped.

I am in the process of making my first braggot as well, but I went with a double fermentation using aler yeast first and then splitting the 5 gallon batch (1/2 for beer and 1/2 for braggot and pitching a wine yeast). When primary was done on the ale yeast I had an FG of 1.020 and the recipe I used had a predicted FG of 1.018.

As far as the hydrometer goes, specific gravity or Brix, they are both going measure the density of the liquid and that is going to include any unfermentables.

The degree of fermentability (which is to say, the amount of "unfermentables") in beer wort is determined by the kind of malts used and the conversion process (both temperature and time) experienced in the mash, and the conditions of the boil. When using malt extracts, the mash has been done for you and the resulting sweet wort concentrated into the extract. Thus, with extracts, you do not control the fermentability of the raw ingredients. However, different brands of extract will vary in fermentability. Furthermore, "light" extract is generally more fermentable than "amber", which is in turn more fermentable than "dark" extract. Many brewers recommend using only light extract to be able to better control fermentability through the addition of specialty grains. Extract brews made with dark extracts typically wind up with high FGs.

When using malt (as grain, not extract), the kind of malt influences the amount of fermentable sugars. "Base" malts such as pilsener, pale, munich, vienna, etc. contain mostly starch. Mashing conditions will determine the percentage of sugars vs. dextrins. Crystal malts have been stewed, converting the starches to sugars & dextrins within the grain. Higher color crystals will be increasingly less fermentable and will contribute fewer sugars as they burn off during kilning. Roasted malts are generally not very fermentable, though often these malts will contribute little more than color and flavor as most starch/sugar has been burned away.

You can look up mash temperature vs. fermentability details if you like. The basic idea is lower temperature means more fermentable.

Lastly, boiling influences fermentability through kettle carmelization and the formation of melanoidins. Basically there are chemical reactions going on in the kettle which join sugars, proteins, etc into larger molecules. These will have distinct colors and flavors. They are also less fermentable or unfermentable by yeast. Several conditions lead to more conversion of sugars into other molecules, leading to high FGs: long boil times, very vigorous boil (too much evaporation), low boil volumes (partial boil), poor heat conduction (local hot spots cause burning), poor mixing when adding extract (heavy extract sinks to the heated bottom and burns). I'm sure I missed some too, but you get the idea.

Hopefully that helps. Without knowing what "beer grains" you used, it's hard to say what effect they might have had. I'm not familiar with the fermentability of Munich extract, but you might be able to look that up or ask where you bought it.

You might consider blending in a very fermentable solution such as honey-water. (Perhaps use a 1 lb/gal mixture which should be around 1.040.) If your yeast are still around they should eat up the simple sugars and thin the braggot out.