Enzymes. Now that's a new word to me 
Sorry. This can get pretty deep if you let it.
BLUF: Brewing is a series of natural processes. Your job as a brewer is setting up the conditions so these naturally occurring reactions work most efficiently and to your favor.
There are numerous naturally occurring enzymes that perform different functions. Basically they convert X to Y at certain pH and temps. I’ll put some charts below that can give you an idea [1]. They’re from a book I recommend you read:
How to Brew by John Palmer. There are free earlier versions online but the latest edition has some updates in it that could be worth your while if you’re interested in going further in the hobby.
Malt extract is concentrated wort. You reconstitute it by adding water. The problem with some extracts is they have complex sugars that some yeast can’t ferment. This is a result of the production of the extract. 1.020 seems to be a common stopping point.
Windsor yeast cannot metabolize maltotriose (a complex sugar). It would have to be broken down into simple sugars that that yeast strain can metabolize.
So, the yeast metabolizes all it can and then stops. That’s why adding more yeast probably won’t get you anywhere. The yeast you already used metabolized all the sugars it can.
In this case, you
could add enzymes like those found in
Brutzyme that enable the hydrolysis of starch and dextrins into fermentable sugars that yeast can ferment. It works best at a temperature range between 50-68°F and a pH of 4-5.5.
*If* you choose to use it, use it with this in mind: this stuff works.
However, in your beer, a high FG in a Amer Brown Ale may not be a huge problem. In fact it may turn out great as is. Brown Ale is not normally known for a crisp, dry finish. The higher finish gravity may be a good thing.
[1] Of the enzymes listed here, I normally only target alpha and beta amylase:
Topic: Tried experimenting just for fun (Read 536 times)
