I have a stalled 2nd gen Mac rum wash. OG was 1.070, which seems low, and FG is 1.030 with a slight sweet taste. It might actually be fully fermented but the FG seems high and the sweetness is unexpected. It's only my 3rd wash so as a learning experience I've tried a few things to get it going again with no luck. I am now considering just running it. Will the unfermented sugars cause any problems like burning or scorching? It'll be run in a 4 plate bubbler with the 1st gen low wines.
The ingredients were for 45l
- 4l trub
- 15l dunder (1st gen, stripped to 55% ABV so some residual alcohol, cooled down overnight because it was getting late)
- 5.4kg raw sugar
- 5.4l feedstock molasses (Bundabeg Refinery)
- Hot and cold water to 45l at 30C
The molasses, sugar and hot water was added to the cold dunder and mixed to 30C. This was added to the trub and topped up to 45l at 30C with unfiltered tank water. The mix was stirred with a paddle then a drill and paint stirrer to oxygenate. The lid and airlock was installed and the fermenting freezer set to 30C with no cooling. pH was 4.85.
After about 4 hours there was no activity so pitched 40g of Lowans yeast, sprinkled on top and lightly stirred in. The following day there was plenty of bubbling and the temp had risen to over 34C (temp was taken with the STC-1000 probe taped to the side of the fermenter).
Airlock activity stopped 3 days later. SG was 1.030 with a slight sweet taste. pH was 3.8 (which didn't seem extremely low) but added 1tsp of calcium carbonate and stirred it in.
There was still no activity the following morning. pH was 4.72. SG was 1.030. Added 2tsp DAP which was possibly unnecessary.
There was still no activity the following morning and the SG stayed at 1.030. pH was 4.8. I added another 40g of Lowans yeast, just in case I'd managed to kill the rest off.
Nothing happened by the next day and the SG stayed at 1.030. At that stage, I decided to just run it and see what happens. The heating was turned off on Tuesday and I'll run it on Sunday, so hopefully it'll clear a bit by then.
I'm not sure what went wrong but my suspects are:
- Too much dunder except pH was 4.85. Perhaps too much alcohol remaining?
- Unfiltered tank water
- Stuffed up the sugar & molasses measurements (possible)
- Mis-read the OG/FG but the wash still tastes sweet (confirmed by 2 others)
- Poor quality molasses but it's almost direct from the mill
I plan to use some of the dunder in the next wash but drop it back from 1/3 to 10%. I think I'll discard the trub in case there's something in there killing the yeast.