Received a warm vial of White Labs Hefeweizen. Made a starter 24 hrs ago with 2c water and 1/2c of DME. After 12 hrs, there was noticeable settling at bottom of flask and it seemed that the starter had all been "used up", so I created a 2nd of the same quantities. Yeast dead or alive seems to drop out of suspension quickly. No krausen is forming.
How do I know if this vial was a dud or not?
Just a heads up, but you likely added way too much DME to that starter. You should never measure DME by volume, only by mass. The rule is 1 gram of DME per 10mL of water. Thus, for 100mL (0.1L) water you would use 10g of DME. In your case, you used 2c of water (~470mL), so you should add about 47g of DME.
You added 1/2 cup, which equates to about 3oz or 84g, which is almost double what you should have used. This would give you a OG of 1.067, which is quite high for an ale starter.
Also, 12 hours is way too short for older/less viable yeast when you don't use a stir plate. If the yeast is fresh, then 16-24 hours is sufficient. Yeast that is <50% viable should go for at least 2 days, I prefer up to 3 to be safe. There's no harm in letting it go an extra day to be sure.
Also, you shouldn't be just adding "a 2nd [starter] of the same quantities" to the original volume. You should cold crash for a minimum of 24 hours (ideally 72), decant your original starter wort as much as possible, then add the new volume of fresh starter liquid onto the yeast cake.
So in short, you added too much DME and didn't wait long enough to let the yeast do their thing.
