FG Issue

Depends what you are brewing...lighter colored pale ales (IIPAs) benefit the most without affecting mouthfeel too much, IMHO. Imperial Stouts ,Barleywines, etc. sometimes benefit from going the other way (adding extract instead of sugar.)

 

You really should read How to Brew. The benefit of re-hydrating yeast is that more survive the transition to being active, and fermenting. While they are in the packet they are inactive, and in your case above, you tossed them into concentrated sugar water. That was just too much osmotic pressure for a lot of them, and probably a few million cells lysed (burst because they could not maintain their cell membrane). I think most people would suggest rehydrating yeast, and in the case of your big beer, using 2 packets of yeast. Google: re-hydrating yeast, and making a yeast starter.

 

http://www.howtobrew.com/section1/chapter6-5.html

 

Below is a post from a past thread:

Why shouldn’t you pitch dry yeast? It's called osmosis. Wort has a high concentration of sugars and the dry cells have a hard time taking in the water. Also the wort will be under the optimal temperature range. So what happens is the yeast die. “Skipping hydration kills about half the cells pitched” (1). They are killed because there cell walls are damaged to the point where they rupture spilling their guts into the beer “Besides only having half as much yeast needed, the dead cells immediately begin to break down and affect the beer flavor” (1) . That statement is what tells me that while GreenKrusty’s observation (dead yeast as food) has merit, there are extenuating factors that trumps it. Yes, there are viable cells left. Cells that have weak cell walls. Healthy cells walls are important to regulating what passes in and out of the cell. Low viability can cause “Slow/stuck /incomplete fermentations””Declining/low viability” “Sulfur””autolysis” (2). A study made also suggested that dry yeast rehydrated in wort can cause a high degree of esters, acetaldehyde and “hot” alcohol character. (3)


(1)p.146 “Yeast, The practical guide to fermenting beer”
(2) p.279,281,273 “Yeast, The practical guide to fermenting beer”
(3) http://seanterrill.com/2011/07/29/dry-yeast-viability-take-two/

in general
http://www.hbd.org/hbd/archive/3301.html#3301-4

Where the above came from:

http://www.beeradvocate.com/community/threads/dry-hop-question.71358/page-2#post-4033115

 

It's not overkill. In my humble opinion, it would not be wrong to always replace a pound of extract for a pound of sugar, regardless of style. For bigger gravity beers, like >1.080 as you suggested, you could go even more, maybe 1.5 lb for 5 gallons. Seriously. This will ensure good final gravity.

All this being said, some extract manufacturers do a better job at fermentability than others. If you're having any issues hitting final gravities, then do the replacement, always, for every batch. But if not, if you can successfully get a 1.055 OG beer down to 1.012 reliably, then nevermind, don't bother with the sugar.

In my experience though, most extracts are 60-70% fermentable. It would be nice if they were closer to 80%. But most are not. I don't recall name brands as it's been many years since I was all-extract, but suffice it to say that there are indeed significant differences between brands and I know it remains true today because the same complaints come up today as I had 15 years ago.

As for rehydration of yeast......... I don't bother. Not ever. And it turns out fine every time. I've heard the theories a zillion times. But in practical experience, it really doesn't matter. And there have been several other experiments recently (look at BYO and brulosophy.com?) that proved no real impact of rehydration vs. not.

 

I knew it wouldn't be long before a non-rehydrator said they never rehydrate and never have any problems. Of course, science has provided some solid reasons to rehydrate, but it's hard to trust those pesky scientists when your beer turns out subjectively "fine".

 

Back off, man. I *am* a scientist. And BJCP Certified. And I've tasted my beers blind many times in competitions against many others where I couldn't pick out my own. Occasionally I win said competitions. It's all good.

It's also a scientific fact that beer contains copious amounts of dihydrogen monoxide, which when inhaled even in small amounts can lead to asphyxiation!

Rehydrate if you want. No one's holding a gun either direction. Many scientists don't find it necessary. It comes down to theory vs. practical results.

 

Of course it isn't necessary. It makes beer either way.