High Gravity Beer. Pitch More Yeast?

[DeBAD]

We are brewing an Imperial Stout (5 gals) from a MW Brewing extract kit. Pitched the yeast Saturday Nov 16th about 7:45 pm at a wort temp of approx 75. SG was approx 1.9. However per the instructions only used one rehydrated package of dry yeast (Safale Ale S-04 Whitbread Strain). My fermentation room is a dark room with a constant temp between 68 to 70.

Took about 12 hours to start fermenting but once it did was like a freight train. Hooked up a blow off tube, put bucket in a water bath with a couple ice bottles and managed to get the temp down to approx 63. Lots of krausen coming through the tube, even starting seeping under the bucket lid. To be safe I even put a couple 2x4s with 20lbs of weight on top of the bucket because so much pressure was building up it seemed like it was gonna blow.

Long story short we weathered the storm and after approx 36 hours of aggressive activity it has slowed down to normal levels. Still getting plenty of bubbling in the blow off bucket (approx 100 bubbles per minute) but now its just blow off gases and not krausen running through the hose.

This is my problem. Now that we are three full days into the process I now have read that since we brewed such a high gravity beer we should have used 2 packets of yeast. I even verified the calculation through the mrmalty.com calculator.

Would it do any good at all at this stage to pitch more yeast? Am I going to get a lower APV if I didn't pitch enough? Seems like any damage is already done right and should just ride it out?

A side note you should know is the recipe calls for the addition of a package of Champagne yeast to be added after the primary stage when pitched to the secondary.

Thanks in advance for any help.

 

[hercher]

You might want to go head and add another packet, though I'm not convinced its necessary. The main dangers of underpitching are under-attenuation and certain off-flavors (cardboard). There clearly is plenty of yeast in there now, but as your alcohol level rises, some of it will die off.

A suggestion for future brews: when I brew big beers like this, I like to start fermentation a little cooler. To be sure, it may lengthen the lag time, but I have found that having the fermentation run a little slower makes the alcohol a little less "hot" in the final product.

 

[DeBAD]

Update. We transferred the Imperial to the secondary on Saturday (exactly 14 days), tested the gravity and it was perfect! In fact it's right smack in the middle of the target range already and we plan to leave it in the secondary at least 1-month. We also tasted the sample and man is it good! Didn't detect any off flavors and no hot alcohol taste. Per the instructions we pitched the package of Champagne yeast, added a tbsp of vanilla extract and dropped in the airlock.

Looking back, on day 4 we DID go ahead and pitch the second packet of yeast. Impossible to tell if it did any good or not but since our gravity was right on target I'd like to think it helped a little.

Now we wait, and wait, and wait! Thanks to everyone for all the helpful input!