Starter Yeast Question

[CDS]

Last batch I brewed I decided to make a starter because the yeast (Wyeast London Ale III) was almost 5 months after manufacture date. It turned out perfectly - I had it on the stir plate for approx. 14 hours, and then left it for another 36 hours and then refrigerated the night before brew day. The starter was super active...produced a lot of krausen etc.
My second go with a starter was yesterday evening - exact same process, volume, DME etc, but with Wyeast 1056 (American Ale). It's been off the stir plate now for about 8 hours, stored at about 19.5C, and although there's some activity, it seems barely there compared to my previous starter (see pic). Should I be concerned? If I don't see anything by tomorrow (brew day scheduled for Sunday) should I ditch it or pitch it?

 

[IslandLizard]

It's been off the stir plate now for about 8 hours, stored at about 19.5C,

Why don't you keep it ON the stir plate?
Yeast needs a constant supply of oxygen to propagate, which is what you want to do when building starters, growing new cells. The constant supply of fresh air (oxygen) is provided by the stirring/agitation.

Once yeast starts to grow you'll see a significant change of color in your starter: It turns from a medium/dark brown to a much lighter and creamier color. After that color change takes place, I usually give it an additional 24 hours.
Then either cold crash in the fridge for 24-48 hours, or pitch most into a batch of wort, leaving some behind, as a reserve for a next starter.

Older yeast may need longer to get started and grow her numbers, anywhere from 2-5 days before you see the color change.
Warmer ambient temps (70-80F) work better for growing yeast than colder ones (<68), but it depends on the yeast too.

BrewUnited's Yeast Calculator
Mr. Malty

 

[IslandLizard]

In the picture I can't see the yeast on the bottom. How much is there roughly?

It does not look done to me, especially being WY1056, a medium flocculator. Put it back on the stir plate, it needs much more time. Once it has grown you can pitch directly, no need (or time) for cold crashing, which easily takes another 2 days.

 

[CDS]

Why don't you keep it ON the stir plate?
Yeast needs a constant supply of oxygen to propagate, which is what you want to do when building starters, growing new cells. The constant supply of fresh air (oxygen) is provided by the stirring/agitation.

I was going by the instructions provided by John Palmer in "How To Brew". He recommends taking the starter off the stir plate after 12-18 hours. The rationale provided is that the yeast needs an active period of low oxygen to build up glycogen reserves, which will help it adapt to the new environment after pitching.
I also followed his advice re: starter temperature, which is to start it at as close to the target fermentation temperature as possible to avoid stressing the yeast after pitching.
So much conflicting info out there, it makes me dizzy!
Anyway here's a photo from this morning showing the yeast layer at the bottom. Still a little activity happening - I'm going to go with it and see what happens. All part of the learning process.

 

[CDS]

In the picture I can't see the yeast on the bottom. How much is there roughly?

It does not look done to me, especially being WY1056, a medium flocculator. Put it back on the stir plate, it needs much more time. Once it has grown you can pitch directly, no need (or time) for cold crashing, which easily takes another 2 days.

Here's a pic from this morning showing the yeast layer.

 

[IslandLizard]

Here's a pic from this morning showing the yeast layer.

It looks very clean! Hard to judge the actual volume of yeast like that, but it looks enough for a pitch into a 5-6 gallon batch of 1.060-some, yes.
You could save a little bit out if you want, for a next round starter.

When you're decanting the supernatant, pour some into a hydrometer jar and measure the gravity. See how far it got down.

Did you use a DME:water ratio of 1:10 by weight, such as 200 gr DME in 2 liter of water? That gives you 1.037 starter wort.

 

[IslandLizard]

Don't forget to oxygenate or aerate your wort well right before or right after pitching!

 

[CDS]

Just to close this off in case anyone else had the same questions I had, the starter was fine. Pitched it at 12:30 p.m. - here's a pic of the blow-off tube in a cup of sanitizer 4.5 hours later - lots of suds! Chugging along nicely.
So I learned that I shouldn't expect to see krausen or much activity at all sometimes...for reasons.