us 05 repitch attenuation

[robsan77]

I get about 80 % attenuation from the first pitch but ive just done a comparison.

1038 og

20 litres pitched fresh pack
20 litres pitched with skim from 1042 beer (3rd pitch)

The skim went off straight away and the fresh pitch was always catching up.

On day 3, fresh was 1020, skim was 1016.

However, on day 5, fresh is 1008 (as predicted) skim is 1012.

I kept it at 17.5c for 3 days then allowed to rise to 18.5.

Has anyone else noticed lower attenuation from repitches?

 

[boozy_shoes]

What styles were you pitching into and how did these vary? were the mash temps the same? The attenuation could be down to these factors rather than the yeast.

 

[Hawks]

What styles were you pitching into and how did these vary? were the mash temps the same? The attenuation could be down to these factors rather than the yeast.

from reading the OP I think its a 40 litre batch split into 2 - so the same wort

I've never noticed tbh, but it's interesting.. Could it be due to the fact the original dried yeast is nutrient packed for that first ferment ?

 

[rpt]

Is the skim under pitched or not aerated enough?

 

[robsan77]

Skim def well pitched and aerated. The beer is a light blonde pale ale. The skim was from a light amber pale.

 

[robsan77]

And the skim had fermented the previous beer (light amber) to 1010. It was however, a late skim on day 6.

 

[paulpj26]

Technically re-pitched yeast shouldn't attenuate differently. However, there are so many factors that could affect the yeasts ability to attenuate (Selective pressure, Health of the yeast, differing values of aeration in the worts, etc)

With a fresh pack of dried yeast you will have the right amount of healthy yeast to attenuate the beer to it's predicted gravity.

I'm guessing as it's the 3rd re-pitching you might have also selected the more flocculent but less attenuating yeast to re-pitch from the previous batches?

 

[robsan77]

well, after reading through the yeast book I think I've found the reason It didn't attenuate fully.

Too much over pitching.

I over pitched every generation and it has the effect of wearing out the yeast as they don't replicate as many new cells. Yes the fermentation gets off to a rapid start but runs out of steam.

Lesson learnt.