OK, let me take a stab at this...
If I read the post right (or at least my take on it), The
first part asks, "How can you taste a beer and guess the OG?" Is it FM? Not really, more like experience.
As you taste the beer, alot of things come into play. Body/mouthfeel [is it thin or thick(chewy)?], does it taste of alcohol (ethanol has a flavor). Does it finish dry or sweet? What is the style the beer fits into? All of this steers you toward the answer. Experience plays a big part in this, but it can be learned if some one shows you the ropes, (i.e, puts a name to the things you are tasting.) Just drinking alot of home brew won't do the same thing.
I've always said to new brewers that trying to hit your OG when brewing is important. This will get you closer to the beer you set out to brew in the first place. Most new brewers are more concerned about ending up with a full 5gals of beer (usually by diluting up to the 5 gal mark). Although you can still end up with a great beer, it doesn't help you grow into a better brewer. I think that's the reason we are all here in the first place (and why you are ready this post.)
The
second part about the "low finishing gravity", is relative for the style,OG,etc. The low FG statement here means (to me), "did the yeast finish it's intended job or did it poop out too early." A Barleywine that finished at 1.028 could be considered "low" for the style. But if your Kolsh finishes at 1.014, you finished too high. It might still be ok as a beer (but probably too sweet) it wouldn't be balanced and it would be judged out of style.
Do you have to brew to style? No, but that's not the point. The point is, shooting for something (your target beer) and being able to achieve your goal. It doesn't have to be a recognized style, just the fact that you did what you set out to do. It's all about making the next batch better than the one before it.
Cherrs,
Dr Scott
