Rehydrated my yeast, still took > 18 hours to start

I decided to try rehydrating my two packets of US-05 for this past weekend's 1.090-OG Russian Imperial Stout brew.

Here's the process I followed:

• I pulled a cup of 102ish degree-F water and poured the packets into it after chilling, while I was whirlpooling and siphoning into the fermenter.
• I conditioned the slurry with wort twice to bring the temperature down and acclimate the yeast to the wort's gravity.
• I timed it, and pitched the slurry right at the half-hour mark. Simple, right?

The yeast was definitely proofed and going in the measuring cup.

I did not bother to aerate the wort particularly; not needed with rehydrated yeast, right?

I was half expecting to see activity around the four-to-eight-hour mark, but like usual, I didn't see any airlock activity until well into the next day. It's going like a piston now, but I was wondering why it took so long to get going? Was it the high SG? The fact my ground water is already warm enough that I couldn't get my wort any lower than 73 degrees when my house's ambient temp is 65?

-Rich

1.) You still need to aerate the wort.
2.) You didn't pitch an active starter you simply rehydrated your yeast and pitched them. Pitching an active starter at high krausen you would have seen activity much sooner.

Although the yeast manufacturer says aeration is not necessary because the yeast are dried with all the sterols and nutrient they need I still aerate. Very little oxygen is required for sterol production:
http://woodlandbrew.blogspot.com/2013/01/how-much-oxygen-does-it-take-to-make.html

Most of that oxygen goes to aerobic respiration which produces about 20 times more energy than anaerobic respiration.

here are some tests done on hydrating yeast:
http://woodlandbrew.blogspot.com/2013/02/rehydrating-safbrew-yeast.html

Echoloc8 said:

I was half expecting to see activity around the four-to-eight-hour mark, but like usual, I didn't see any airlock activity until well into the next day. It's going like a piston now, but I was wondering why it took so long to get going? Was it the high SG?

Click to expand...

Probably, you did everything you needed to. Less than 24 hours is perfectly acceptable.