Why why why?

I often start two 5 gal. carboys side by side. They start exactly the same. Same recipe, same juice, same yeast. So why do they sometimes act so differently? Slower fermentation, quicker restart after racking or the amount of foaming?


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Presumably the juice is similar but not identical (unless you mixed the two batches and halved them. Ditto the yeast. Then you presumably place the two carboys in different locations in your cidery. Might one carboy be closer to a heat source? A cooling source?

When you say the same yeast, do you mean that the yeast come from the same vial/pack/starter? Or the same type of yeast?

Carboys as close as possible. Juice same batch but yeast two identical packets. That could be the cause.


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Id say its ultimately down to two things
1. Living things don't always act in a predictable manner.
2. No matter how hard you try you will never get two exactly identical batches. They may be quite similar but never identical. ( one bag of sugar might have a few more grains than the next, One campden tablet may be a little bigger than the other, the glass in one carboy might be a millimeter thicker than the other, etc etc.)

Remember its not fair to play favorites with your yeasty children

MarkKF said:

I often start two 5 gal. carboys side by side. They start exactly the same. Same recipe, same juice, same yeast. So why do they sometimes act so differently? Slower fermentation, quicker restart after racking or the amount of foaming?

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I've seen some good theories here, but the answer is obvious:

I haven't gone to 5 gallons yet, I have 5 one gallon batches going and some are the same and all are different in looks and air lock activity. More/less sugars, more/less yeast, although side by side maybe more/less heat... I can't explain it but they all look good to me.

My workbench has an air duct near one end and moving my carboy 2 feet to the right gets it out of the airflow of that duct. My point is 2 feet or the width or one carboy can put you in a different picoclimate


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Was this brewed and cooled as a 10 gallon batch and then split, or were the batches cooled separately. If one of the batches was 5 degrees or so cooler than the other, the yeast might be slower.

UpstateMike said:

I've seen some good theories here, but the answer is obvious:

Click to expand...

Yeast are aliens. They freely travel about outer space and land where they will. They are able to form neural networks and they can adaptively organize their colonies. They are able to mutate when they think that mutation is best. Their communications networks carry transit traffic for all sorts of other organisms. They possess an awareness that we can not even begin to understand.

Take two identical twin boys. One gets out of bed early and the other prefers to sleep late.

Just goes to show you when something seems not right it usually is.

Turns out the bung/airlock was not making a tight seal. Replaced both and bingo both carboys are bubbling away.


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I build work trucks for a living. We get a bunch of chassis built by the same work shift of the same assembly line, and even they are sometimes different.
Its nearly impossible to perfectly duplicate a complex system. In nature and in manufacturing.