Ramifications of underpitching yeast?

[Pyrenus]

Ok, so I made a dumb, dumb mistake over the weekend.

I was brewing a hefeweizen and had made a yeast starter about 2 days in advance. My starter was kept at room temperature, around 75 degrees.

When it was time to pitch the yeast, I didn't shake up the starter. It had about 1/8" of an inch of "trub" in the bottom of the starter and I carefully pitched the liquid and suspended yeast on top, and tossed the "trub" thinking it was just proteins and settled malt stuff. I know, I know, that was most of my yeast!

I left the fermentation chiller a bit warmer to get started, around 73 degrees.
24 hours later I had fermentation and bubbles. This morning it was bubbling pretty furiously, although the blowoff tube is still clean. I adjusted the fermentation chiller back down to about 68 degrees.

So, knowing that I probably underpitched a little bit, will this hurt the beer at all? Should I plan on leaving it in the primary a little longer than 7 days before bottling?



Lastly, I want to thank you all for being so patient with all the questions from new guys like me. Its amazing how friendly and helpful you all are when faced with these similar questions over and over again.

And I did a quick search but didnt' find anything that matched exactly what I was looking for.

 

[Evan!]

It really depends on whether or not the starter was still actively fermenting when you pitched it. If it was, then there was plenty of yeast in suspension. Even if you didn't it appears that you had a lag time under 24 hours, which is good. I'd say you have nothing to worry about. Just make sure you keep it nice and cool, in the 60's.

 

[Pyrenus]

Thanks for the reassurance. I'm aiming for the banana flavors, so I'm shooting for 68 degrees. The fermentation bucket is staying about 3-4 degrees warmer than the ambient temp, so I'm making small adjustments to get it down to where it needs to be.

The starter appeared to be actively fermenting when it was pitched. It was very cloudy and I could see swirling activity and little co2 bubbles rising up out of it.

 

[TeleTwanger]

You'll lose some sleep and grow a few gray hairs but other than that nothing.

 

[Loup]

Despite the common misconception, yeast isn't really needed for fermentation. Instead, it is merely food for the tiny beer demons. If you neglect to provide the beer demons with enough yeast, they will steal your jelly doughnuts in retaliation. This may not sound all that bad, but just imagine never being able to eat a jelly doughnut ever again.

If you neglect to give the demons any yeast at all, they will simply piss in your beer, which will make it taste horrible.

 

[Saccharomyces]

Underpitching in a clean American lager would be a disaster. The yeast growth would cause some ester production and maybe even diacetyl. Underpitching in a hefe where you want esters and other fermentation byproducts like isoamyl acetate ban, you are fine. I intentionally use small starters for beers where I want the yeast character and deal with the long lag time by being extra careful with my sanitation.

Sometimes the best teacher is experience.

 

[phissionkorps]

Can someone provide any actual science about how underpitching would produce a lot of off flavors, etc? Off-flavors are the result of compounds yeast produces when stressed. I can't think of a single organism where abundant and easily available food is a stressor. Whether a large or small starter is pitched, yeast will continue through its natural growth cycle in the same manner.

 

[Saccharomyces]

New Lager Brewing by Noonan I think is the best resource on the subject. Byproducts are primarily produced during the growth phase. Shorten the growth phase and you limit the number of byproducts.

There is a limited supply of oxygen in wort. Once the oxygen available is used up, yeast cells limit reproduction, leaving fewer stressed out cells to finish attenuating your wort. It's like the situation in a big company after a layoff. The guys left have to do the work of the guys who were pink slipped, so they aren't very happy.

Besides growth, pitching from a vial you get yeast which has depleted some of its reserves. Building up a starter replenishes the reserves so the cells are ready to chomp away. Nutrient deficient yeast cells will flocculate without reaching full attenuation, resulting in a high finish gravity and leaving more byproducts around since they aren't done doing their job when they get too tired to keep going.

 

[Edcculus]

Under pitching could lead to stressed yeast and more esther production. They could crap out early, but probaby not. Since its a hefe, increased esthers probably won't be a problem.

 

[carnevoodoo]

"A long lag time leaves the wort susceptible to contamination by bacteria and wild yeast. The increase in yeast growth that goes along with low pitching rates is also associated with increases in diacetyl, esters and fusel alcohols. Finally, under-pitching can result in under-attenuation ÷ causing high final gravities ÷ or an extremely slow fermentation. "

BYO - Beauty and the Yeast

 

[phissionkorps]

I don't think yeast really "gets tired" since a generation time is so short. Reproduction is limited as resources are limited, leaving less cells because fewer cells are reproducing. Therefore, since resources are decreasing, available "work" to be done is also decreasing, as total cell count is decreasing. Just because conditions aren't good for an organism to wildly reproduce on an exponential level doesn't mean that conditions aren't good. Also, even if unfermented sugars were left, I find the premise that that causing any detrimental effect to the yeast themselves counterintuitive. If you eat until you're full, is it going to be more detrimental to you if you only eat 90% of the hamburger? Certainly not. Regardless, (and I hope no one thinks I'm being stand offish or anything), does anyone have any real science that explains this? I.e. peer reviewed scientific journals...brewing publications don't count, especially since some them tell you autolysis = cannibalism

I could be 100% wrong, which is totally fine, however I am trying to understand why an organism in perfect conditions would be producing compounds it produces when stressed.