Just an observation on residual sugars in dunder and how they affect your starting gravity
I thought it was time to do another rum run, so I dug out 10L of dunder I had saved from my last rum adventures.... nearly 2 years ago. This was 100% boiler stillage from a stripping run of Macs Rum using stock feed molasses and sugar and stored in a big green shed 10L plastic jerry can. At the time I put the boiling dunder in the sterilised jerry and sealed it, similar to the way I would hot cube a beer wort so it would remain sterile (I hadn't heard of 'live' dunder at that time).
Anyway, I opened it up the other day, it smelt file, just like the day a stored it, no growths or other yuckies so I bunged 2 litres of it in with 5kg of Bundaberg Molasses, the usual nutrients and made up to a 20L wash. I expected the SG to be about 1.070ish but the measured gravity was way up at 1.085 :o
I checked the gravity of the dunder and found it to be 1.055. I'm sure the wash it was recovered from finished about 1.010. I can only think the unfermentable sugars from that wash were concentrated when boiled down in the stripping run. All these extra unfermentables will impact the finishing gravity of my current wash, though I checked it this morning and its down to 1.025 and still going strong.
I can see now why, with so much unfermentable sugar available bacterial infection thrive in 'live' dunder.