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Fermentation mystery

Paganbagels

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Hoping someone could help unravel a mystery.  The same beer fermented in two glass carboys in the same location ended up with very different fermentation profiles and final gravities.

I and a friend recently brewed a ten gallon batch of a Belgian Holiday Ale using a keggle and immersion chiller. Wort was split into two glass carboys. Both carboys sanitized with Star San. One had been sanitized and then sealed a few days prior to brew day, the other was sanitized just before transfer. The yeast was a Belgian strong ale from white labs and it was pitched up to a 400ml starter via stir plate.

Fermentation was vigorous for both, in fact both air locks had to be unclogged and cleaned. The carboy that had been sanitized several days before brewing finished at 1.010, the other carboy finished at 1.030.

Carboys were left to ferment in a heated garage under blankets and next to each other. Could residual sanitizer have caused a slower fermentation?
 
There are possibly false assumptions in your post that may explain differences in fermentation results:
1) Equal sanitation results. The sealed carboy may have been sanitized well, the second not and the bacterial count somehow higher. Carboys and transfer devices equally sanitized?
2) Was the wort quality equally pitched, not just fluid volume? (Not just quantity, but quality).
3) Yeast starter equally pitched? Were the yells cells equally distributed, and were there a sufficient number for both batches?
4) Were O2 levels in wort sufficient in both?
Assuming you're positively "yes" about #1 and #2, then perhaps there was a difference in #3, and it really required more yeast, and/or #4, where the 1.030 carboy needed more oxygen for the cells to do there job. Or, it needed a nutrient addition.
I'm sure the experts in the forum can add a lot here.
 
good thoughts from ethan, i'm particularly curious about #3 and #4.  how did you split the yeast? 

what was the OG?  what was the volume?  how many packets of yeast did you use?
 
I wonder if the carboy sanitized just prior to wort transfer was sprayed with star-san. I use it and it works great, but it requires time, and actually needs to dry out to effectively sanitize. For instant use the sulfite solution is better, but requires a good rinse, then starsan. I also wonder about the effect of too much residual star san slowing up the fermentation.
 
Unless you left a boatload of StarSan in the carboy...say more than a quart,probably more... It would have little effect on the fermentation.  StarSan only works by having a pH of approx. 3. Once you water it down with 5 gal of wort it will have no effect. Look at Berliner Weiss. it's brewed sometimes around 3.5pH with a blend of yeast and lacto.
 
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