Determining the bitterness units in beer is often done by calculations based on raw materials and boil time. After all not everyone has easy access to a well equipped brewing lab.
But how accurate are the calculations, and which method of calculation should you use? Several different methods exist, each giving different results.
As it's something I've pondered myself I was interest to see that someone has carried out research into this question:
Multiple small batches (20–80 L) of beer were brewed, varying different factors each time, including boil time, starting gravity, hop variety, hop addition (time and amount), hop type (pellet versus whole leaf), and yeast variety. The α-acid concentrations of hops used in the study were measured using HPLC, and the IBUs were calculated using the three formulas based on the measured concentrations. The BUs of the finished beers were determined by isooctane extraction followed by spectrophotometric absorbance at 275 nm. The iso-α-acid content of the finished beers was also measured using HPLC.
Three methods of calculating Bitterness Units were used and:
Interestingly, the measured BUs for most of the beers analyzed matched the Garetz calculation of IBUs most closely.
I still prefer to have hard data rather than estimates but sometimes you have to make do. The rest of the abstract can be read here.
Friday, 31 January 2014
Saturday, 18 January 2014
Making Malt
The first stage, screening the grains for size and clearing out stray bits of straw was fun:
Most of the process takes place in the steeping and germination vessel:
The steeping and germination vessel wins for shinyness but doesn't move as fast.
The grains will get three steeps, with air rests in between so the grains don't drown. During the germination stage the drum will rotate to stop the rootlets tangling. Kilning next...
Wednesday, 15 January 2014
Premature Yeast Floculation
Premature Yeast Floculation (PYF) is a little understood brewing problem that causes poor fermentations and makes me think of Kevin "Bloody" Wilson.
I heard Professor Alex Speers of Heriot-Watt University give a talk about the other day and I wanted to write up my notes so I though I'd share them with your all. It's fascinating stuff.
Premature Yeast Floculation
Fermentability is related to yeast flocculation: early flocculation causes poor fermentation leading to flavour and filtration problems.
Floculation is reversible and adding the chelating agent EDTA or some sugars can cause yeast to un-floculate.
A number of factors affect flocculation: FLO and other genes coding for proteins such as zymolectin, mannan, oxylipin and affecting the charge on the cell.
Environmental factors also have an effect such as:
The negative effects of PYF on beer include:
PYF is believed to be caused by factor/s from barley or malt. Possibly due to fungal infection, pressure during steeping, malting CO2 levels, other barley stresses.
Malt made with low O2 water may be implicated.
In breweries malts are blended by variety, year and maltster so it makes problems hard to trace!
Laboratory methods have been adapted to use smaller scale fermentations than tall tubes using 15ml of congress wort (9°P) +4% glucose at 21°C (three repetitions).
Measure turbidity/density. Use SMA yeast (a German lager strain).
Describe the °P change and absorbance change on graphs. Statistics will need to be used to look at the curves.
Test tube fermentations are slightly poorer than actual fermentations due to early yeast setting as a higher proportion will have settled out before CO2 starts being produced.
Looked for an anti-microbial peptide in malt that may have been affecting the yeast but they didn’t find it so looked for larger compounds.
Tried different degrees of filtration of wort and found a 100 kDa fraction causes PYF. Arabinoxylan may be involved, possibly with a linked peptide.
During PYF yeast has less surface charge. PYF flocs are more tightly bound than control flocs.
Barley exposed to different fungal pathogens was malted and brewed with. Infected malt caused PYF, more disease resistant barley varieties caused less PYF.
PYF malt has higher FAN
Lab analysis of malt tends to stop at wort production so fermentation not included.
More studies needed on:
I heard Professor Alex Speers of Heriot-Watt University give a talk about the other day and I wanted to write up my notes so I though I'd share them with your all. It's fascinating stuff.
Premature Yeast Floculation
Fermentability is related to yeast flocculation: early flocculation causes poor fermentation leading to flavour and filtration problems.
Floculation is reversible and adding the chelating agent EDTA or some sugars can cause yeast to un-floculate.
A number of factors affect flocculation: FLO and other genes coding for proteins such as zymolectin, mannan, oxylipin and affecting the charge on the cell.
Environmental factors also have an effect such as:
- Sugar
- O2
- CO2/turbulence (keeps yeast in suspension)
- Cell age
- Fimbrae
- N
- Temperature
- pH
- CSH (hydrophobicity)
- Ethanol
- Ca2+
The negative effects of PYF on beer include:
- High sugar levels
- Irregular flavours
- Yeast autolysis
- More chance of infection
- Lower ABV
- Higher diacetyl
- Money losses!
PYF is believed to be caused by factor/s from barley or malt. Possibly due to fungal infection, pressure during steeping, malting CO2 levels, other barley stresses.
Malt made with low O2 water may be implicated.
In breweries malts are blended by variety, year and maltster so it makes problems hard to trace!
Laboratory methods have been adapted to use smaller scale fermentations than tall tubes using 15ml of congress wort (9°P) +4% glucose at 21°C (three repetitions).
Measure turbidity/density. Use SMA yeast (a German lager strain).
Describe the °P change and absorbance change on graphs. Statistics will need to be used to look at the curves.
Test tube fermentations are slightly poorer than actual fermentations due to early yeast setting as a higher proportion will have settled out before CO2 starts being produced.
Looked for an anti-microbial peptide in malt that may have been affecting the yeast but they didn’t find it so looked for larger compounds.
Tried different degrees of filtration of wort and found a 100 kDa fraction causes PYF. Arabinoxylan may be involved, possibly with a linked peptide.
During PYF yeast has less surface charge. PYF flocs are more tightly bound than control flocs.
Barley exposed to different fungal pathogens was malted and brewed with. Infected malt caused PYF, more disease resistant barley varieties caused less PYF.
PYF malt has higher FAN
Lab analysis of malt tends to stop at wort production so fermentation not included.
More studies needed on:
- Comparison of yeast strains
- Varietal tests and resistance to pathogens
- Malt house effects (especially CO2)
- Hull less barley
- Treatment and re-use of steep water
- Mode of action
- Relation to cell toxicity
Friday, 10 January 2014
Bugs in old beer
Not really news but I've noticed a microbiological analysis of old beer brought up from a shipwreck from the 1840s has been carried out. Four species of lactic acid bacteria have been cultured, and whilst no viable yeast cells were found they do say some of the cells resemble brewers' yeast (Saccharomyces cerevisae) and other Dekkera. For those not familiar with the latter it's the current technically correct name for Brettanomyces.
The presence of these organisms is only as expected really but it's nice to see historical evidence.
The presence of these organisms is only as expected really but it's nice to see historical evidence.
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