I'm dragging over the dry yeast rehydration topic from Ozzy's thread:
http://thehotpepper.com/topic/56562-ozzys-all-grain-on-deck/?p=1221012
So, apparently if you pitch dry yeast into wort, there's a best case of 30% cell death, and a worst case of 50% ...
In fact, there are extra cells in the packets assuming that people will pitch dry, so that the remaining cells meat the cell counts typical of normal to mid-gravity wort. This has been tested over and over, you can pretty much count on 50%, I guess, from what I read.
Modern dry yeast for brewing has been dried with a bunch of oxygen, and the yeast has been stuffed w/ trehalose and glycogen to protect and enable it to best deal w/ the first few seconds of hydration, when the liquid outside is allowed to pass through the membrane unimpeded.
When you rehydrate dry yeast, the clock starts ticking on those and other building blocks.
So, in pitching dry yeast into wort, we're getting a little bit of unwanted wort into the yeast at first, at the end of the day ...
Now ... on the other side of the coin, there's rehydrating ... lots of variables here, many of which are hard to control on small-batch homebrewing scale ...
Wrong temp ... killling ...
Warm dry yeast into cooler liquid leads to the production of petite mutants that never grow or ferment properly and make H2S ...
Mmm, rotten eggs! =)
Too high a quantity of water for the yeast leads to increased hydrostatic pressure that bursts the cells more efficiently than wort ...
Sanitation is interesting, too ... especially because yeast like to make chorophenols from chlorine and chloramines, and apparently from sanitizer solution as well.
Mmm, band-aids! =)
If you boil to remove the chlorine etc, you nuke the oxygen and precipitate out the baking soda and you have a similarly toxic yeast environment not dissimilar from distilled or RO water ...
The timeline for dry yeast rehydrated in water
with GoFerm to help protect it is apparently like 15-30 minutes ... wait too long, killing yeast again, and worst it consumes it's contents pretty fucking quickly, I read ... and you have to balance this time w/ getting the wort and the rehydrated yeast slurry to within 5-15F of one another, too, or you can shock the yeast
that way ...
One of the yeast scientist Dr dude's says the rehydrating solution should contain 0.5 - 1.0% yeast extract - and frankly, I'm not even sure what yeast extract is, or if it's available to homebrewers ...
A lot of water softening systems deionize, making them similarly bad to distilled/RO ...
If they don't deionize, I guess they swap calcium and magnesium ions for sodium and potassium ... I guess this affects the flavor or beer, especially AG beer ...
Using these wrong waters, the guts get sucked out, and using wort, the wort gets sucked in ... which is why a dilute wort is best, as per Dr Cone.
Apparently, also, any amount less than 105F and most yeast are leaching their insides out ...
Dr Cone says to use a 0.9% saline solution to rehydrate the yeast, optimally.
GoFerm comes from the wine industry and is designed to provide dry yeast what it needs while rehydrating, I guess ... sterols and minerals.
Now, getting back to what water we would use ... apparently that's complicated, too ...
A Brita doesn't cut it, the filter has to be
ACTIVATED carbon filter, and you need to run water through it as a
VERY slow rate ...
For a dry yeast for use in wine, the time line is listed similarly, saying you must provide food within 30 minutes, or the yeast will begin to all at once starve, deteriorate, and lose viability ...
There's some other crap that suggests that 15 mins is the sweet spot for pitching, not 30 mins ...
Now, back to pitching into wort. 30-50% death, but the other parameters are all out ...
There's 20 billions cells/gram in the packs, with 11 grams or so, for a total of 220 billion cells ... a little more than double the cells of a liquid vial, and not by accident ...
I think I'll pitch dry and figure on 50% loss and avoid trying to keep dechlorinated-but-not-deionized water right at 105F, w/ a necessary hardness of 250-500 ppm, at roughly exactly 10x the weight of a very small amount of yeast, and without cooling such that cold water's drawn into the cell, or getting too far in temp from my wort to pitch into and shocking it otherwise ...
Dude, fuck all that.
I think I just substantiated why you've done well pitching US-05 directly.
* Lots of information gleamed from numerous sources, but a back & forth between Dan Listermann (Listermann Manufacturing and Listermann Brewing Company) and Dr Clayton Cone (Danstar, I think) is what most of those sources led back to.