After fermenting and aging for about four months, I decided
to open up each brettanomyces lambicus sample and take the fermentative
measurements. Oddly enough, all six of
the White Labs samples finished out right around 1.0043 specific gravity while
all of the Wyeast samples finished out at 0.
Granted that each of my samples fermented for about 3.5x the length of
those in Yakobson’s study, I still was a little surprised that the initial
concentration of lactic acid didn’t play a bigger role in the final gravity of
each beer. In his Wyeast sample, there
was nearly double the percentage of apparent attenuation between the 0mg/L
sample and the 3000mg/L sample and yet in my results, they ended up nearly
identical.
Although the disparities between the two are not strikingly
large, the Wyeast beers did end up with slightly lower pH than the matching
White Labs beers. I’m not sure if this
is telling that the Wyeast strain produces slightly more acid than the White
labs version or if it has to do with the slightly different levels of
attenuation. If the White Labs beers
were able to ferment all the way down to 0, would the pH be more similar?
As fun as the empirical data is to look at, my main reason
for this experiment was because I wanted a subjective view of the flavor. So, on September 15th, six of my
homebrew club friends, each with sophisticated palates, gathered for a blind
tasting. Although I knew that a few of
the participants had read Yakobson’s dissertation, I wanted to keep the details
of my experiment a surprise and so prior to the tasting, only one other person
in the group was aware of what we would be sampling. I also wanted to be able to participate
blind and so at the time of bottling, I randomly selected samples from the
batch and transferred them into consecutively numbered bottles (I did keep index notes though). Four weeks later at the tasting, when I
poured each bottle into the individual sample glasses, I had long since
forgotten which bottle was which beer.
Each participant was given one sample from each of the 12 variants
at the same time along with a score sheet to record their perceptions and
preferences. Since Yacobson’s study
showed dramatic changes in four ester concentrations based upon the initial
levels of lactic acid, I included these four flavor profiles (Ethyl Acetate –
Solventy, Ethyl Lactate – Buttery/Creamy, Ethyl Caproate – Fruity/Wine, and
Ethyl Caprylate – Fruity/Apple) as well as two other characteristics
(Goaty/Funky and overall sourness). In
addition to these flavors, I also asked the participants to rate each sample
based on what they determined to be the overall “Brettiness” of each sample as
well as their overall satisfaction with each one. All ratings were based on a 5 scale with 5
being the highest.
Mean ethyl lactate scores for Wyeast seemed to increase as
the initial concentration of lactic acid increased, but after 1000mg/L, the
perception of the ester dropped off. A
similar occurrence happened with the White Labs strain except there was a near
equal level of detection between the 1000 and 3000mg/L concentrations. This is interesting to me because in
Yakobson’s study, there was a clear correlation between the acid and ester and
the concentration of the ester seemed to increase at an exponential rate as the
acid increased. In my results, we didn’t
really see that and in fact, the overall highest perception occurred at
1000mg/L.
The mean ethyl acetate scores for my results differ
considerably from what Yakobson found in his study. Similar to ethyl Lactate, from an initial
concentration of 100mg/L of lactic acid, there was a slight correlation between
the ester and the acid concentration. We
see a somewhat similar patter with the White Labs strain starting at about the
500mg/L concentration, but with Wyeast, at the same mark the two are basically
inversely correlated.
Interestingly enough, my results for Ethyl Caproate are
almost entirely opposite of what Yakobson found. In general, this is one of the esters that he
basically found to decrease in concentration as the amount of initial lactic
acid increased. My results show that our
perception of the ester generally increased along with the lactic acid
concentration. It’s interesting to note
that again Wyeast peaked in flavor around the 1000mg/L mark whereas with the
White Labs strain, starting at the 100mg/L mark, there’s a pretty consistent
increase in ester detection as the lactic acid increases.
A somewhat similar ester to Ethyl Caproate, our Ethyl
Caprylate detection varied by strain. It
appears as though we had a growing detection of it up until the 500mg/L point
with the Wyeast strain, after which the level fell closer to the mark at 0mg/L
of lactic acid. With the White Labs
strain though, our perception of it was all over the map and it does not appear
that there was any correlation to the lactic acid concentration levels. Both of these results were contrary to what
Yakobson found though.
In addition to looking at the specific, individual esters, I
asked my participants to taste each sample and rate them based on their contentment
of the overall “brett” flavor. This is
difficult concept to quantify since each participants’ perception of what brett
really tastes like can differ and their individual preference for certain
esters associated with brett vary, but overall, I wanted to see if there were
any noticeable trends. It turns out that
with the White Labs strain, there definitely appears to be an increase in
perceived “brettiness” up until the 1000mg/L mark after which the perception
essentially levels off. Although there
was a big drop between 0 and 100mg/L acid concentration, starting at the
100mg/L mark we see a similar pattern with the Wyeast strain. It appears that perceived “brettiness”
increases with the lactic acid concentration up to about the 2000mg/L mark.
So how does all of this add up? Assuming that these results were repeatable
every single time, I suppose if you wanted to tailor a beer to have a certain
flavor profile, you could look above for the ester that you want to profile and
then choose the initial concentration of lactic acid which resulted in the
highest perception of said ester. If you
want a mixture of the esters resulting in the best flavor profile, what’s the
best method? With the data that I
gathered, I went about this in two different ways.
In the first method, for each level of initial
concentration, I took the six flavor profile scores and created one overall
mean score. As you can see in the Wyeast results above, it
appears as though people thought that the greatest concentration of flavors was
to be had at the 500-1000mg/L initial acid concentration level. With the White Labs strain, the results were
a little more mixed. In general, flavor
concentrations were greatest at, or above, 1000mg/L with the highest overall
flavor rating at the 3000mg/L mark.
In addition to aggregating the individual flavor ratings, I also asked each participant to rank their top three favorite samples based on overall flavor and general satisfaction. To compute a final score and rank, for each 1st place vote, I awarded 3 points, 2nd place I awarded 2 points, and 1 point for each 3rd place vote.
In addition to aggregating the individual flavor ratings, I also asked each participant to rank their top three favorite samples based on overall flavor and general satisfaction. To compute a final score and rank, for each 1st place vote, I awarded 3 points, 2nd place I awarded 2 points, and 1 point for each 3rd place vote.
Although the Wyeast 3000mg/L sample came in first in terms
of total number of votes, based on the scores, the top preference was actually
the White Labs 2000mg/L sample. Even
though these results don’t match perfectly with the aggregated scores above,
the White Labs result is fairly close since the 2000mg/L sample tied for 2nd
in terms of highest score with the aggregates above. To me though, it’s maybe more interesting
that the 3000mg/L Wyeast sample received the most votes when that sample above
had five other samples with higher aggregate scores. My assumption is that this has to do with my
participants’ general preference for increased acidity. Whereas the ratings above were based on
ester/flavor concentrations, the votes and scores were based on which sample
they liked the best. Since the 3000mg/L
sample had a fair amount of aggregated flavor and a higher level of acidity, it
makes logical sense that they might rate it higher than say a sample with a
slightly higher level of combined flavors but with much lower acidity. Unfortunately this theory doesn’t hold up so
well when you look at the 3rd and 4th place samples…
Overall, the experiment was a lot of fun to conduct even
though the results didn’t mirror those that Yakobson found. I was expecting to see stronger correlations
between the esters and the initial levels of lactic acid, and although we didn’t,
I think the results that I found proved that perceptions don’t always match up
with reality.
Even though I attempted to recreate Yakobson’s project as
best I could, I’m still fully aware that my experiment was not without flaws
and the two don’t match up perfectly. If
I were to replicate it again, I definitely would like to take fermentative
readings at the 35 day mark to see if the attenuation rates ended up closer to
what Yakobson found. As for the tasting,
profiling six different esters between twelve different beers is a big
challenge and I think I would restructure the tasting a bit to help with this
task. First, I might break the tasting
down into two sessions of six samples.
While it was fun to try the White Labs and Wyeast samples side by side
to see how they differ, I believe that if we were to only judge the six samples
from one strain at a time, we wouldn’t run into palate fatigue as quickly and
our scores might have been spread apart a bit more than they were. Related to this, I think that using a 5-point
rating scale clustered the results too much and for future ratings, a 10-point
scale would allow for a little more variation.
Lastly, I failed to provide everyone with a benchmark sample first. Without this beer to calibrate our palates,
the first sample that each of us tried probably averaged three points across
the board since we didn’t have anything to compare the concentrations of flavors
against (it’s impossible to know though since I asked everyone to start at
different samples and move about the group randomly).