Would you care to drop some wisdom on me as to the composition of the unfermentables? And would they be broken down by an amylase enzyme? It would be much appreciated.
many people and a lot of sources will list various fermentability percentages for extract. feel free to disagree with me anyone, but i find brews that are all or mostly extract, especially darker ones (which will contain crystal malt) generally will not reach the same degree of attenuation as an average (150-154F) mash of allgrain. 1.071 to 1.023 is definitely what i would expect from your recipe. if it tastes alright, then drink it
i do extract brew because it can shorten the brewday hugely, so i generally do two things:
1. low gravity beer that is mostly extract for fermentables. something like 4lbs of light DME to provide fermentables and 2 to 4 lbs of grains to add flavour, ie. crystal, roasted, munich, amber etc. the lower attenuation works out fine, because the OG is simply lower, FG ending up between 1.008 to 1.015 depending on yeast and stuff
2. if im making a very strong beer i will do an all grain mash of maybe 12-14lbs, which sort of starts to max out the potential of my cooler mashtun, then add 2 or 3lbs of DME and/or sucrose/dextrose/candisyrup. this is how i make beers with OGs higher than 1.075