I just learned that it is always a good idea to check the correction factor that applies to your refractometer. A commonly accepted correction factor for converting a refractometer’s Brix reading to a hydrometer Plato reading is 1.04. I was always under the impression that the Brix reading has to be multiplied with this value, which works for me, but Sean Terril pointed out to me that the commonly accepted formula divides the Brix value by this correction factor to covert to a Plato reading. (Refractometer Calculator)
Since my approach was working for me I had to check what’s going on here. I thus tested water, a 20 Plato sugar solution and a 20 Plato wort with both the hydrometer and my refractometer. All solutions and the refractometer had the same temperature.
hydrometer in water
This is the hydrometer in water. I have a table that I use to correct the hydrometer reading in Plato for temperature and the slight offset that the hydrometer has
water on refractometer
water measured with the refractometer
hydrometer in 20.4 Plato sugar water
The sugar water (~40g table sugar, 160g water) read after correction 20.4 Plato
hydrometer in 20.4 Plato wort
The wort read after correction 20.4 Plato as well
20.4 Plato sugar water on refractometer
In the refractometer the sugar water read 19.4 Brix. Since refractometers are calibrated for sugar water, it should have read 20.4 Brix
20.4 Plato wort on refractometer
In the refractometer the wort reads 19.5-19.6 Brix (remember that water read slightly under the zero-line). To get the hydrometer reading I have to multiply this reading with 1.04
The reason why my correction factor is different is that the scale on my refractometer is off. I.e. there is already a conversion factor for sugar water that is not 1. But since I checked my refractometer against my hydrometer at various wort gravities and found that Plato is Brix * 1.04 I can still use this refractometer in brewing.
BTW, the ATC of this refractometer is also broken. For every brewing session I have to re-calibrate it with water. Since this is done very quickly, it doesn’t bother me too much.
This may sound crazy, but I commonly hold the “Diacetyl rest” at 22 C (72 F) for my lagers. When reading through some German brewing papers I notices that some of them referred to a fermentation schedule where the lager was fermented at 8 C (46 F) for about a week and after that the beer temperature was raised to 22 C for 1-2 days before the beer was crash cooled to near freezing for cold conditioning.
In my brewing it takes a bit longer than a week for the beer to be done with primary fermentation. It also doesn’t reach final gravity as fast as it was shown in those papers. To make maters worse, fermenting the last few fermentable sugars until the attenuation is close enough to the attenuation limit always tends to take longer than I want it to.
To speed things up I started holding the “Diacetyl rest” rest around 20 C. I intentionally put diacetyl rest in quotes since for most of us the primary benefit of this rest is not diacetyl reduction but speeding up yeast’s consumption of those last fermentable sugars.I prefer to call this rest a maturation rest and may hold it for up to a week, if the beer is still too far away from its attenuation target. (If you don’t know how to determine final extract or gravity target of the beer, check out the Fast Ferment Test.)
Warm fermentation and lagers doesn’t seem to go together, but don’t worry. Low fermentation temperatures are only needed during primary fermentation when the yeast is actively growing and its metabolism shows activity along many different pathways that can leak excessive esters and higher alcohols if the temperature is too high. Once the yeast is done growing and all nitrogen sources have been assimilated, the fermentation temperature can be raised without the risk of creating the flavor compounds that are generally associated with high temperature fermentations.
keg with heating pad and temperature sensor
I do these maturation rests in kegs for a number of reasons. First, I can easily heat them with a heating pad controlled by a temperature controller. Second, I can use this fermentation to carbonate the beer. Lastly, the yeast will consume all the oxygen that is introduced during racking.
The image above shows how the heating pad (you’ll need one that doesn’t have an automatic shut-off) is attached to the bottom of the keg. At the top of the keg I attach the temperature sensor, covered with a piece of foam.
When the beer is racked to the keg, I make sure plenty of yeast is transferred as well. The kegs have a shortened dip tube, which allows for transferring the beer and leaving behind the yeast sediment later.
Finally the whole thing is wrapped in a blanket for further insulation:
Keg wrapped in a blanket
A pressure gauge is attached to monitor the pressure build-up and allow controlled CO2 release.
I finally ran a brewing experiment again and am dusting off this blog to post the results.
The experiment was a repeat of a standard experiment that evaluates yeast growth in still, intermittently shaken and stirred starters. I like how easy it is to set up and plan to repeat it again.
Setup
919g of 12 Plato wort were aerated to 100% air saturation on a stir plate. Then 7.8 g WLP 830 yeast sediment from a primary fermentation was added and allowed to un-flocculate completely. The cell density was determined as 22.3 Million/ml with a hemacytometer. If you do the math you find that the slurry contained a total of about 20 Billion cells which means its density was 2.63 Billion/g. Previous slurry density assessments for slurries from yeast propagation ranged from 4-5 Billion/g for this yeast. I assume that trub played a big role in the reduced cell count in this slurry.
Once the yeast was evenly distributed in the wort, the wort was evenly divided into 3 500 ml Erlenmeyer flasks. The flasks were labeled with their empty weight and covered tightly with aluminum foil. I didn’t tighten the cover intentionally. I noticed that this happens when I grab the flasks at their neck to shake them. I made sure that all of them had tightened aluminum foil caps, even though only one would be shaken intermittently.
All starters were allowed to complete fermentation. One sat still, one was shaken intermittently (1-2 times in the morning and 3-5 times in the evening) the last one was placed on a stir plate and stirred continuously. A vortex formed on the stir plate, but was eventually covered with foam when CO2 started escaping. The ambient temperature was around 18 C.
Data:
Once fermentation was complete the yeast was allowed to settle into a dense cake until the beer on top cleared. The beer was poured off and the flask’s weight with yeast and stir bar (in one of the flasks) was determined. From that, the empty weight and the stir bar weight the yeast weight was determined:
starter type
total extract in starter (g)
final yeast weight (g)
estimated sugar utilization (Billion cells per g)
still
36
10.8
1.4
intermittent shaking
37
10.2
1.3
stirred
37
13.1
1.7
I only recorded the yeast weight and did not count the yeast with the microscope. Simply, because I did not want to spend too much time on this. To estimate the number of cells grown I assumed that the sediment had a density of 4.7 Billion/g, an average of the numbers I had assessed in earlier experiments.
Discussion and Conclusion:
The wort volumes for the three starters were not exactly the same, hence the difference in the extract weight.
I was surprised to see that the sill and shaken starters showed no difference in the amount of yeast that was gown from the available extract. This is different from the data reported by others (e.g. the great Maltose Falcon article on yeast propagation: Yeast Propagation and Maintenance: Principles and Practices) where a shaken starter grew significantly more than a still starter and a stirred starter outperformed a shaken starter by about 4x. The caption to the chart mentions that the data point for the still starter was taken from a different experiment, though.
Data I recorded on past yeast propagation steps (usually stirred) and fast ferment tests (usually shaken) show more difference in extract utilization for yeast growth, but there are also a number of other parameters that have been different for those experiments. Most notably the starting gravity and the initial cell density.
I’ll have to repeat this experiment in the future to see what covering loosely with aluminum foil does and what an airlock would do to the extract utilization that can be achieved. And maybe I also find the time to count the final number of cells.
Getting back into brewing seems to be plagued with all sorts of obstacles. This time I ran out of propane before getting the wort to a boil. And yes, it was at night again and I was far from being in the mood for a midnight propane run.
But this time I got the wort up to 98 C, which is hot enough to pasteurize it and I decided to go a different route – the no chill approach. While the wort was still hot I covered it with aluminum foil:
The wort sat this way over night on the deck and I moved it into the house in the morning. After 24 hrs the temperature dropped to 32C. During that time the pH fell from 5.27 to 5.14. I’m not sure if this is sign of an infection, but it smelled just fine. So I brought it to a boil. A lot of coagulation already happened in the hot wort and an oddly brown layer of trub developed during heating:
Other than that the boil seems to be going as normal.
Could there be something stronger than the IPA (or KaIPA for this matter) itself?
Yes, the beer that can be squeezed from the spent dry hops. Something only a true brewing geek knows to enjoy. Besides being murky like the Ganges in the rainy season, the aroma is pronounced but not overpowering. The bitterness, however is much harsher than the actual beer. It particularily lingers in the back of the throat, which I don’t appreciate too much.
Last weekend I brewed my annual Maerzen using 75% Best Malz Vienna, 20% Weyermann Munich II and 5% CaraFoam. When designing the brewing water I went by my past experiences with a similar grain bills that used Weyermann Vienna and the surprise came when I tested the mash pH. Instead of the expected 5.5o I got 5.77. I’m generally not off by that much and was doubting the pH meter until I also tested the mash pH with colorpHast strips. During the decoction the pH fell to 5.71 and I added another 2 ml 88% lactic acid to bring it down to 5.58, which I considered ok for a Maerzen. The boil pH was later reduced as well with some lactic acid.
After testing the distilled water pH of this Vienna malt I found that is was way off from the pH one would expect from a base malt slightly darker than pilsner malt. It was 5.8. Below is a chart of the distilled water mash pH for various base malt samples that is taken from my mash pH paper:
The pH is slightly higher than pale or pilsner malts and more than 0.2 pH higher than the Weyermann Vienna that I tested a while back. This goes to show that the color/pH correlation is even weaker than I thought and that one should not rely on the accuracy of color based mash pH estimations for grists that contain a mix of base malts. The color based mash pH prediction works much better for grists made of pale/pilsner base malt and a mix of specialty malts since the pH properties of the latter are more predictable.
More predictable was the amount of lactic acid that I had to add to lower the pH. With 0.32 ml per kg and 0.1 pH drop it was well within the 0.25-0.42 ml range that I show here.
The malt analysis sheet for this batch of malt reported a pH of 5.9 for the congress mash. While I noticed this I assumed that the pH of the congress mash, which is diluted to 8 l/kg towards the end, would not be that useful for predicting mash pH. In hindsight this could have been an indication for the higher than expected mash pH.
Some may remember the experiment where I added life yeast to a few bottles of last year’s Imperator, my Doppelbock. I posted the rather pronounced flavor difference when I tasted 2 bottles side-by side here.
Tonight, about 1 year after they have been bottled, I opened another pair of these bottles.
The beer from the non-yeasted bottle still has a pronounced dark fruit aroma whereas the beer from the yeasted bottle has a much more subdued aroma. It seems to be catching up since I remember even less aroma at the 6 month tasting. In this beer some of the roasted character is coming though which is overpowered by the other aromas in the non-yeasted beer.
Quite dramatic this time was the difference in head retention. While it took the yeasted beer only 6 min until the head collapsed to a thin layer of bubbles. The head of the non-yeasted beer lasted about 4 min longer. This could be attributed to the release of protease-A by the yeast. This enzyme is known to degrade head retention positive proteins in beer.
As for the difference in taste, it follows the difference in aroma. The non-yeasted beer has a decidedly fuller and more complex taste than the yeasted beer. Without having experienced the difference side-by-side I would consider the yeasted beer a great Doppelbock but it is not as good as the one that was bottled without the yeast.
Conclusion: I stand by my opinion that yeast gets in the way of the proper development of the flavor profile of a Doppelbock and brewers should avoid bottle conditioning this beer.
On my last batch I put my dissolved oxygen meter to good use and tested the effectiveness of an wort aeration device that some brewers use. This device is a pipe with several small holes. As the wort flows through the pipe it pulls in air through the holes (Venturi Effect). The air then mixes with the wort and oxygenates that wort.
Building this device is simple. I used a 12 inch copper pipe in which I drilled 20 small holes. The holes are clustered around the top. The pipe was sanitized in boiling water and attached to the end of the vinyl tubing used for racking the wort from the boil kettle to the carboy.
The extract content of the wort was 11.0 Plato, its temperature 15 C and its volume 16 l.
I noticed that when wort is flowing through the device air is not necessarily drawn in. If this is the case some movement or shaking of the pipe is necessary to start the inflow of air which is accompanied by an audible gurgling. I did not pay attention to that at the beginning and as a result about ¼ of the carboy were filled without the device actually pulling in air.
Another problem was the substantial development of foam which required 2 pauses in order for it to settle so filling could continue.
Once the 5 gallon (18.9 l) carboy was filled to the 16 l mark. I swirled the wort around in order to provide some mixing action.
The resulting aeration in the carboy was about 4.5 ppm which is 3.5 ppm short of the 8 ppm that are recommended for most medium gravity ales and 7.5 ppm short of the 12 ppm that are recommended for lagers.
The problem with this device is that the air bubbles it creates are not small enough for an effective O2 transfer between air and wort. While a lot of foam was created, this foam had much larger bubbles than the fine foam that is created by using a mix-stir or a sintered stone for aeration. Both these methods have shown better performance in wort aeration (not yet published data).
To test this aeration method further, a 1 qt Mason jar was filled with about 1 pint of wort through the perforated pipe. The resulting oxygen content was about 3.5 ppm. Closing the jar and vigorous shaking it for about 30 s boosted the wort oxygen content to 7.3 ppm which is close to oxygen saturation possible with air (about 8.0 ppm).
It should be noted that these are the results of one limited experiment and that they can not necessarily generalized to say that aeration with a perforated pipe always leads to inadequate wort oxygenation.
Many brewers wonder what difference
bottle conditioning makes in brewing. One aspect of bottle
conditioning is the presence of live yeast its effects on the aging
beer.
Based on an on-line discussion, which I
had with fellow brewers, I designed an experiment where I added a
small amount of live yeast to my Doppelbock when I bottled the
carbonated beer after cold conditioning.
The recipe, which I brewed about 7
month before this sampling, was very similar to the recipe posted on braukaiser.com. It was brewed with an enhanced double decoction. The
first week of primary fermentation was done at 8 C (46 F) and the 2nd
week was done at 10 C (50 F). This was followed by a 1 month
maturation at 12-13 C (54-56 F) during which time the beer was racked
off the primary yeast into a Cornelius keg with shortened dip tube
where it was allowed to reach its final gravity of 4.8 Plato. To help
this maturation the beer was kraeusened with WLP830 (German Lager) 2
weeks into this maturation rest even though the primary fermentation
itself was done with WLP833 (Ayinger Lager). The attenuation going
into the following cold conditioning was 73% while the attenuation
limit of the wort was 76.6%. During the maturation rest the beer also
built up natural carbonation.
The beer was cold conditioned for about
1 month and 2 weeks and then bottled straight from cold conditioning
at 1 C (34 F) into chilled bottles. The bottles were not purged with
CO2 prior to filling. Oxygen scavenging caps were used because these
were the only ones I had at hand. 3 of the bottles received about 300
Million cells of an active WLP830 (German Lager) culture. This
yielded about 1 Million cells per ml in these bottles. No sugar or
other fermentables were added since the beer was already carbonated.
After bottling the bottles were stored
in the basement. The ambient temperature started at about 13 C (56 F)
at bottling time and rose to about 17 C (64 F) over the following 3
months. 2 days before sampling the bottles were cooled to 10 C (50
C).
3 month after bottling and about 7
month after brewing I sampled a bottle that was bottles without
additional yeast (non-yeasted sample) and a bottle that was bottled
with additional yeast (yeasted sample) side-by-side. At the time of
sampling I knew which was which but didn't know what to expect from
the yeasted sample.
Aroma:
The non-yeasted sample showed the
typical dark fruit (including black currant) and malt aroma of a
German Doppelbock with a hint of alcohol while the yeasted sample
showed a much more restraint aroma. The malt notes and dark fruit
notes were rather faint. The aroma was more that of the young beer.
There was also a hint of alcohol in its aroma.
Appearance:
Both beers were clear at serving
temperature. The yeasted sample formed a thin, yet dense, yeast layer
on the bottom of the bottle.
Foam stability:
My standard foam stability test is to
take a Koelsch glass, pour the beer down the middle to let it foam up
until the foam reaches the top of the glass. Then the time it takes
for the foam to collapse and show the beer surface is taken. For both
samples it took more than 13 min for that to happen.
Taste:
The taste experience was similar to the
aroma experience. The non-yeasted beer showed a much stronger and
more complex taste while the yeasted sample was more subdued. Both
samples did not exhibit any off-flavors. In both cases the bitterness
was low and did not linger into the finish. The non-yeasted sample
was a bit sweeter which was also reflected in its lower attenuation
Mouthfeel:
Both samples exhibited the same
mouthfeel.
Stats:
non yeasted beer
yeasted beer
OE
18.0 Plato
attenuation limit
76.6%
yeast addition
none (actual residual yeast count was not
assessed)
~ 1 Million/ml
yeast viability at tasing time (methylene blue
staining)
n/a
~ 60%
AE
4.7 Plato
4.5 Plato
attenuation
74%
75%
attenuation delta
2.6%
1.6%
pH (beer)
4.50
4.51
The yeasted beer did ferment a little
further since at bottling time a small amount of residual fermentable
sugar was available as can be seen from the attenuation to
attenuation limit difference of 2.6% for the non-yeasted beer.
Conclusion:
The result of this tasting did surprise
me yet supports my thinking that the hallmark flavor of German Bocks
and Doppelbocks is in fact the product of oxidation and staling of
the beer. It is assumed that the yeasted beer sample did not exhibit
that flavor as strongly since the yeast was able to scavenge the
oxygen that had been introduced during the bottling process.
The added yeast did not affect the head
retention negatively in this case. One way it can do this is by
releasing excessive amounts of Proteinase A into the beer which can
break down foam proteins.
The pH was not negatively affected
either which is a sign that there was not an excessive amount of
yeast autolysis or not enough yeast to make a difference.
The idea that big dark beers benefit
from small amounts of post fermentation oxygenation has also been
brought up by fellow home brewer Fred Bonjour and warrants further
investigation into optimal oxygenation rates ad well as aging times.
When reading up on brewing Weissbier (also known as Bavarian Wheat) one of the suggestions is a ferulic acid rest. This rest around 43 C
(110 F) works best at a pH > 5.7 and liberates ferulic acid into the
wort. This ferulic acid is the precursor to 4-Vinyl-Guajakol which is
responsible for the the clove flavor produced by Weissbier yeats. The
more ferulic acid there is in the wort the more 4VG should be produced
by the yeast and the more clove character the beer should have.
This
is what I wanted to test. So I brewed a Weissbier recipe twice. Once
with a simple Hochkurz mash and another one with an additional 30 min
43C rest at a pH > 5.70. For the second beer acid malt was added at
61C. This is above the optimal range for protoelytic activitry since I
also wanted to limit the protein degradation during the time the mash
spent in the 45-55C range.
The following table lists the process steps taken for the 2 beers:
0.52 g/l Hallertauer Tradition 6.8% for 60 min (added before
start of boil)
0.52 g/l Hallertauer Tradition 6.8% for 60 min (added before
start of boil)
Yeast
WY 3068; 1000 ml Kraeusen
WY 3068; 1000 ml Kraeusen
primary
7 days at 18.5 C
6 days; started at 16C and was raised to 20C over the next 3
days. Fermention seemed done after 3 days. But it was stuck at 5
Plato.
Lowered temp to 12C while WLP830 (W34/70) was prepared.
While at 12C for 10 days the gravity fell from 5.7 to 3.6
Plato. Beer was racked off old yeast, WLP830 Kraeusen was pitched
and the beer was bottled at 3.8 Plato.
Carbonated at 17C for 10 days
maturation
5 days at 10 C;
10 days at 17C for carbonation;
see primary
Note that the fermentation for the 2nd
batch slowed down signficantly after it reached a gravity of 6 Plato.
At this point I decided to pitch a lager yeast and I cooled the beer
for the time it took to propagate that yeast. This was to drop out most
of the original yeat and limit autolysis. This was unplanned and I hope
it is not the reason why the results of the experiment are like they
are.
Tonight I tasted the two beers:
82
Weissbier IIIa
83
Weissbier IIIb
age
7 ½ weeks
5 weeks
aroma
slight clove
slight banana
not much difference
slight clove
slight banana
not much difference
head retention
fairly stable
not much difference
fairly stable
not much difference
appearance
dark golden color
dark golden color
taste
sweet start that finishes with a distinct clove note which
lends the beer some bitterness
not much difference between.
The clove note seems to be at the same level.
sweet start that finishes with a distinct clove note which
lends the beer some bitterness. There seems to be a tad more other
yeast character present
otherwise not much difference
The clove note seems to be at the same level.
mouthfeel
average mouthfeel
(compare to standard German Pils)
average mouthfeel
(compare to standard German Pils)
stats
original extract: 11.75 Plato
limit of attenuation: 77%
actual attenuation: 77%
apparent extract: 2.7 Plato
pH: 4.25
original extract:12.7 Plato (I got better efficiency than expected)
limit of attenuation: 78%
actual attenuation:78%
apparent extract: 2.8 Plato
pH: 4.11
Conclusion: For the chosen yeast holding the ferulic acid rest
didn't make any noticeable difference in the clove flavor that was
produced during fermentation. While additional experiments should be
made to confirm these findings it is very much possible that this rest
is not worth the additional work.
(comments are disabled b/c
of problems with spammers. Send your questions and comments to kai at
braukaiser dot com)
