I have personally added alpha-amalase to a stuck fermentation at room temp which took the beer from 1.040 to 1.000. No new yeast, no new 02, no heat, just the enzyme. This personal experience inclines me to believe that this enzyme (while perhaps less active) is still very much active at room temp.
You're confused on dextrins. Dextrins are long chain (not short chained) complex sugars. The amalase will break these down.
As for adding more extract, there are plenty of ways to add it to a fermenter without introducing o2 or having issues getting it into solution. I simply offered a possibility, not my recommendation.
dextrin [′dek·strən]
(biochemistry)
A polymer of D-glucose which is intermediate in complexity between starch and maltose.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, I
I misquoted the enzyme. It's denatured over the temp range not under. And long chain, complex sugars are called starch.
Amylodextrin is a linear dextrin or short chained amylose (DP 20-30) that can be produced by enzymatic hydrolysis of the alpha-1,6 glycosidic bonds or debranching amylopectin. Amylodextrin colors blue with iodine.
(Beta) Limit dextrin is the remaining polymer produced by enzymatic hydrolyse of amylopectine with beta amylase which cannot hydrolyse the alpha-1,6 bonds at branch points.
(Alpha) Limit dextrin is a short chained branched amylopectine remain, produced by hydrolysis of amylopectine with alpha amylase.
Starch Structure
Starch is a glucose polymer composed of two primary molecules; amylose, straight chain glucose residues linked α-1-4 to the starch and amylopectin, which is a similar molecule linked to the starch at α-1-6 positions. Amylose comprises approximate 25% of the total starch molecule. Google for starch creative commons for a starch molecule helix.
Alpha-Amylase
α-amylase is an endo-enzyme that acts only on α-1-4 links in a starch molecule. It essentially targets these links randomly, with the exception of α-1-4 links in the immediate vicinity of a α-1-6 branch point. Because of the random nature of the links targeted by this enzyme, α-amylase quickly breaks down complex starch molecules.
The random nature of the way α-amylase acts also limits the amount of fermentable sugars generated by this enzyme. Only when it acts on the end of a glucose chain does it liberate glucose, maltose or maltotriose, which tends to happen only towards the end of mashing.
α-amylase generally tolerates high temperatures well, and works most effectively at a temperature range of 65°C-75°C (149°F-167°F).
Beta-Amylase
β-amylase works differently from α-amylase in that it acts only on the non-reducing end of glucose chains of a starch molecules, releasing a fermentable maltose sugar. The enzyme will eventually shorten the chain until it reaches a α-1-6 branch on the starch molecule.
The resulting unfermentable starch is commonly referred to as a limit dextrin, which is one of the major components which provides body in the finished beer.
Unlike α-amylase, β-amylase is quickly denatured by high temperatures, with an active temperature range of only 55°C-60°C (131°F-140°F). To limit the speed the enzyme is denatured, a thick mash is generally effective, limiting a water to grain ratio of no more than 1 quart/pound.
