Can I wash and reuse yeast from previously underpitched beer?

[bandrek]

I recently brewed a 30L batch of beer using only half a packet of dried yeast. The instructions told me to use the full packet. The beer came out enjoyable, it wasn't a bad batch or anything, it was just lacking some of the fruitiness associated with that strain of yeast. I definitely had better results in the past. I realized I had underpitched this my yeast. But my question is can I still harvest the yeast and use it to make a starter for my next batch?

 

[Bassman2003]

I would not unless you do a multi-stage starter from a small amount to ensure your next batch is full of new, vibrant yeast. Not overworked, tired and old yeast.

 

[seatazzz]

What yeast did you use? Pending answer to that question, what I would do is brew another beer using the entire slurry (don't wash, just get as much of the slurry/gunk from the fermenter as you can into a sanitized glass jar). What you did is create a starter; depending on your original gravity, there may just not have been enough yeast cells to finish it. Now in that slurry that's left over, you have a beautiful starter for your next beer. Just my two cents, but I've been using yeast slurries for several years now, and if you treat them right they will treat your beer very right.

 

[pvtpublic]

I came here to say the same thing as seatazz.

 

[bandrek]

What yeast did you use? Pending answer to that question, what I would do is brew another beer using the entire slurry (don't wash, just get as much of the slurry/gunk from the fermenter as you can into a sanitized glass jar). What you did is create a starter; depending on your original gravity, there may just not have been enough yeast cells to finish it. Now in that slurry that's left over, you have a beautiful starter for your next beer. Just my two cents, but I've been using yeast slurries for several years now, and if you treat them right they will treat your beer very right.

I used safale be 256. I actually already harvested the slurry and decanted the yeast, now I have a small jar of this yeast. I think I might just make a starter out of of this. Based on your answer I assume that would be okay?

 

[seatazzz]

Depending on how much slurry you got, a starter might not be necessary. Slurry has all the things a starter does; viable yeast, yeast nutrient (which is basically dead yeast cells), and protein. If you washed it, then yes do a starter with some DME or LME, whatever you have on hand; or even do a mini-mash on your stove with some base malt. Another option, that I have used many times, is what is called a vitality starter; instead of making a starter a day or two before brewing, pull off some first runnings after mashing; cool it to about 72°, then add to your yeast. Gives it a bit of a head start.

 

[IslandLizard]

pull off some first runnings after mashing; cool it to about 72°,

That's a good idea, I sometimes do that too!

Note to @bandrek, the OP.
If you go that route, I would pasteurize that pulled off wort first, by giving it a 5 minute boil in a small pot on the stove, then let it cool (in a sink or tub with cold water).
Also, the gravity of that starter wort should be around 1.040 ideally, but could be a bit higher, perhaps up to 1.060.
Cover with a sanitized lid, of course, until ready to pitch. Make sure your yeast is within 10°F of the wort when adding it.

The main batch of wort will need to be oxygenated or well aerated (whisk) right before or right after pitching the yeast starter.

 

[aceluby]

Pitch your next batch right on the yeast cake