Inconsistent fermentation at Youngs

I'm currently processing the Youngs records from 1990. They're fun, because they are so complete. Loads and loads of information crammed into them.

What's particularly good is that the results of laboratory analysis are included. With handy things like pH, colour and bitterness. Which is where a surprise came. The inconsistency of the bitterness levels.

John Hatch, former brewer at Youngs, mentioned that the FG of one batch could vary a lot acroos different fermenting vessels. The main cause being the difference in size and form of the vessels they had installed. This was why they would blend post-fermentation, to even out the differences.

I hadn't expected to see even bigger differences in bitterness levels across the different types of fermenters. Which, I suppose, was another good reason to blend.

I'm using as an example a single-gyle brew of Special Bitter on 3rd April 1990. The batch was split across four fermenters: numbers 20, 24, 25 and 29. The volume of beer in each varied considerably.:

FV 20    85 barrels
FV 24    144 barrels
FV 25    376 barrels
FV 29    110 barrels

I'm pretty certain that the three smaller vessels are all older rounds. Whereas the large vessel is clearly one of the 400 barrel cylindro-conicals.

This is the fermentation record:

The conical fermenter was pitched a couple of degrees warmer. Though it was one of the rounds that hit the highest temperature. The conical had the lowest FG of 1009.5º. While two of the rounds only got down to 1011.5º.

The lab results are even more diverse:

 

The bitterness levels vary from 33.5 to 39.5 EBU. That's quite a range. With the most bitter beer from the largest volumes. The biggest difference is in the yeast count, however. Which is way higher in the conical. Interesting, that.

I can't help wondering if these beers tasted noticeably different. With their varying FGs and bitterness levels, they surely must have.
 

Listen to brewer John Hatch explain how they brewed at Youngs in the 1990s.