Why would one batch of beer, brewed the same as the second, be more bitter?

Question

In fear of going into too much detail and yet not providing enough information to ascertain possible reasons;

Does anybody have any reasonable hypothesis as why one batch of beer would be more bitter than a second batch when re-produced exactly the same?

Does anyone have any answers as why this may happen?

The best information I can provide are my records.

It stands to reason there will be more questions of me before possible answers can be provided, and I'm happy to provide more information.

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reply dated 9/12/14

Firstly thank you to those who responded, I have lunched myself into exploring the information provided to isolate my possible reasons for this batch being higher in bitterness.

I do feel as I have failed to provide the correct information in order to portray my situation. I beg your forgiveness and have provided the TWO offending records.

Thus I will endeavour to provide more information and dismiss possible instances that could be causing the fault.

'To eliminate the variables will assist in finding my mistake'.

NOTE: I have now found out how to use OneNote and this should help to read my records.

Batch #218 was in fact my best beer! - #218 did achieve a second place in the local show, thus my perseverance to reproduce it.

The problem batch is #220!

From my observations there are two note worthy differences between the batches:

1. The addition of Gelatin to clarify the beer when kegging. Could this be the problem? - NOTE: I hope to disprove this issue once the bottled #220 ( that has no Gelatine ) has had sufficient time to carbonate - will update in the future.

2. Not taking an accurate time in the first batch when the Cacao Nibs where added to the adjunct boil.( #220 notes where taken - 30min before the end of boil ) From memory # 218 had the Cacoa nibs added as late as 10 min before the end of the adjunct boil, but I can not be sure. Could this be the problem?

The deciding factor to use Fining's in #220 was that #218 was 'cloudy' and did not present well when pouring a beer.

At the risk of lay it all out for everyone to see I have included my tasting notes. Some comments are brutally honest! - Please see the humour in them.

Might I add that procedurally I have developed what I consider a ridged set of procedures when brewing, my reasoning for this is to be able to reproduce a beer, and I have very successfully achieved this many times before. But alas 'brewing is an art within the science'.

To answer some comments:

HOPS - To my knowledge the hops was of the same batch, only difference was the date utilising the hops from making #218 and #220 - less than a month. ( hops stored in air tight container in fridge)

WATER - All my brewing water is filtered, two stage down to Carbon 0.2 Micron. I currently do not take PH readings as I have not ventured into Full Mash Brewing, YET!

Yeast - Both S04 Safale of the same vintage ( stored in fridge )

Skimming the krausen - I see the errors of my ways... but in my defence I only conduct this procedure prior to any hops being added.

FG - Well I do not have and answer to why the FG of #218 was so high "1.019" - Seeing as it was my first attempt at using the Cacao Nibs with an English Bitter I presumed the FG of 1.019 was due to the extra addition of the Nibs!?!?

The more I review my post I see many avenues that may contribute to my problem, but I hope someone else can see my glaring mistake!

Answer 1

Your notes indicate that with this batch (218) you are back to using S04 as the yeast. If batch 208 was brewed using a different yeast that is probably a big part of the answer. Different yeasts hold onto hop oils and alpha acids in different ways. Its quite possible that you'd notice a perceived difference in IBUs if the yeast was different.

This is also true if the pitching rates were different as well. But if you are using dry yeast that's likely not a factor if you kept the same pack size each brew.

Your notes also seem to indicate skimming the krausen before adding the nibs. The krausen usually contains a lot of hop oils in it as well. Some of those get back into the beer after the krausen falls. If you skimmed it out then you'd have less IBUs in the brew too.

Tell me if I am at all close to understanding your notes (which I think are great BTW). I'll edit my answer if new info becomes available.

EDIT: What the heck I'll add one more thing. What was the FG of batch 208? This FG at 1.019 is a little high. Residual gravity can have a profound effect on perceived bitterness too.

EDIT2: I think a strong candidate is the gelatin fining. The fining would have dropped more yeast and protein. All of which hold on to hop resins. Once those things dropped out, your perceived bitterness would drop as well.

Answer 2

I know you say the two batches were brewed exactly the same, but surely something changed to produce the different results. Here are a few possibilities off the top of my head, assuming the recipes are identical:

• Different alpha acid levels in the bittering hops.
• Different levels of sulfate in the brewing water, affecting the perception of the bitterness.
• High mash pH, sparge temperature, or steeping temperature, leading to tannin extraction.
• Yeast bite

I'm sure there are plenty of others I've missed.