Homebrewing Experiments

There is a lot of conventional wisdom in the world of homebrewing. Some of it is good and obvious (always keep things clean and sanitized), while some of it is a little murkier (can you leave beer on the trub for a few weeks instead of transferring to a secondary fermenter)? Many a debate has been had on online homebrew forums, at club meetings, and over homebrews with friends on topics ranging from mash temperature to whether whole cones or hop pellets work better for dry hopping. To try and answer some of these questions, a scientifically-minded crew of homebrewers have been busily experimenting with their brew days to answer some of these burning questions at In this issue, we share their findings for three of our favorite Brülosophy “exBEERiments.”


Arguably, one of the most important components of brewing, responsible for converting the boring starches in a kernel of grain into sweet fermentable wort, is the mash. Without it, we couldn’t make the delicious homebrews we make today. As every all-grain brewer is well aware, there are many variables to consider when deciding how to approach mashing a particular beer, nearly all focusing in one way or another on the variable of temperature. Real scientists have long since understood and spread their knowledge of how mash temperature impacts the resultant wort and finished beer, and since I’ve no interest in pretending to be as smart as them, I won’t go into too much detail.

For the purposes of this experiment, my focus will remain solely on single infusion mashing, characterized by steeping milled grain at a single temperature for a given amount of time. During this so-called saccharification rest, the starches are converted to fermentable sugars by two main enzymes. Here is a simple breakdown of how they work: Beta-amylase is said to be most active between about 131–150 °F (55–66 °C) and chops up whatever gets in its way into smaller bits of mostly maltose, a highly fermentable sugar. Because of this, lower mash temperatures have been shown to produce more fermentable worts.

Alpha-amylase is quite different in that it is more active at warmer temperatures ranging from about 154–162 °F (68–72 °C), converting starches into maltose as well less fermentable sugars and unfermentable dextrins.
In essence, a lower mash temperature purportedly produces a beer with a lower final gravity (FG) that’s dry with a thinner body and crisp mouthfeel, while a beer mashed warmer is said to finish with a higher gravity, and will be sweeter with a fuller body. Obviously, there’s far more to mashing than this, but that’s for another discussion — for this experiment I wanted to know about the impact mash temperature has on perceptible differences.


To evaluate the impact mash temperature has on two homebrews made using the same ingredients, then mashed at drastically different temperatures — 147 °F and 161° F (64 and 72 °C).


For the recipes, I brewed using two Biermuncher’s Centennial Blonde Ale kits from I made a yeast starter a few days in advance using two smack packs, which I would later split on brew day.


A total of 20 people participated in this experiment, including many Beer Judge Certification (BJCP) judges, obsessed homebrewers, and certifiable craft beer nerds. A discriminative sensory analysis method referred to as a triangle test was used to determine distinguishability and involved each participant being served three samples in different colored paper cups — two from the low mash temperature batch and one from the high mash temperature batch. Tasters were then asked to select the different beer. In order to reach statistical significance given the sample size, 11 participants would have had to accurately select the high mash temperature sample, though only 9 of the participants were capable of doing so, implying a general inability for people to reliably distinguish between a beer mashed at 147 °F (67 °C) from another mashed at
161 °F (72 °C).

The nine participants who made the correct selection on the triangle test were asked to complete an evaluation comparing only the two different beers, though they remained blind to the nature of the experiment. It’s important to interpret the following information with caution, as the failure to achieve statistical significance means those who completed this evaluation may have done so by chance.

Four tasters perceived the aroma between the beers as being similar, three thought they smelled exactly the same, and two felt they were not at all similar. Of those who reported noticing a difference, five preferred the aroma of the high mash temperature beer and one liked the low mash temperature beer more. Regarding flavor, six of the nine tasters experienced the beers as tasting somewhat similar, two said they were not at all similar, and one thought they were exactly the same. Things got a little more interesting when it came to mouthfeel, as not a single taster perceived the different samples to be exactly the same, with six saying they were somewhat similar and three believing they weren’t at all similar. A pretty striking majority of seven tasters reported preferring the mouthfeel of the high mash temperature beer. Overall preference was split with five and four tasters expressing preference for the low mash temperature beer and high mash temperature beer, respectively.

At this point, the nature of the experiment was revealed to the nine tasters and they were then asked to select the one they believed was mashed warmer. Only four chose the correct sample.

My Impressions: Regarding my experiences trying to distinguish between the two experiment beers, and even with my obvious bias, I honestly could not tell them apart. As is often the case, I was almost convinced I could detect some very slight differences when I first started pulling pints for myself, but this confidence quickly drifted away as I began to attempt triangle tests served to me by others. At the very least, I expected to perceive a fuller body in the high mash temperature beer, but side by side, I could not tell them apart.


I reckon every all-grain brewer is at least somewhat aware of the impact mash temperature has on wort, most particularly that lower temperatures increase fermentability while higher temperatures decrease it. The objectively observable differences between the beers in this experiment corroborate this scientifically valid fact — the higher beta amylase activity in the low mash temperature beer resulted in a FG of 1.005 while the increased alpha amylase activity in the high mash temperature sample resulted in a FG of 1.014, a strikingly vast 0.009 SG difference. Prior to this experiment, if asked how two beers of such varying FG might differ, I would have claimed the differences in body and especially perceived sweetness would be easily identifiable. It’s a line of reasoning that, on the surface, seems obvious: Higher FG = more sugar = sweeter. The data in this particular instance just doesn’t seem to back this up. But, more likely there’s more to this story — after all, the boil, cooling, and exact fermentation temperatures could have also contributed significantly to the different flavors. While I’ve no good way of measuring it, I’m curious if the types of dextrins remaining in a beer that was mashed on the warmer end of the spectrum are imperceptible to the human palate. This obviously doesn’t explain the fact mouthfeel between the beers wasn’t a dead giveaway, which continues to stump me.

Finally, there is one more aspect of this experiment that didn’t seem to have an impact on the ability for tasters to tell a difference between these beers — level of alcohol. The low mash temperature beer had a calculated 4.4% ABV while the high mash temperature beer clocked in at a much lower 3.4% ABV.  Perhaps higher mash temperatures are the ticket for those who prefer making flavorful examples of big beers with lower ABV.

For the yeast starter, which I started a few days before brew day, I pitched two smack packs of yeast into a single 2-liter Erlenmeyer flask with plans to split it between each fermenter after harvesting some for future use.
I milled the grain and collected the full volume of water for both no-sparge batches the night prior to brewing. I awoke the following morning and began to heat both kettles of water to strike temperature, which took about 5 minutes longer for the high mash temperature batch. To keep things from getting too confusing, I staggered the start of each batch by about 10 minutes.

While I’d considered comparing a simple 10 °F (5.5 °C) difference in mash temperature, I ended up changing my mind and settling on the more extreme ends of the single-infusion mash range: 147 to 161 °F (64 to 72 °C).

Each mash was allowed a 1-hour saccharification rest before the sweet wort was collected and transferred to kettles. This is where I noticed the first rather obvious difference between the batches, with the high mash temperature wort developing a rather large and persistent layer of foam.
Even as the wort was boiling, the foam stuck around the high mash temperature wort, making me wonder if this was an indication of how the finished beers might differ in terms of head retention.
I added the hops at the appropriate times throughout the boil then the wort was chilled and racked to two 6-gallon (23-L) PET carboys. A post-boil specific gravity comparison confirmed that my process was pretty consistent between the batches.

Both fermenters were placed in my temperature-controlled fermentation chamber and allowed to finish chilling to my target fermentation temperature. It took about two hours to reach 66 °F (19 °C),
at which point I pitched the yeast. Signs of activity were present in both carboys just 12 hours later.

I began to notice some differences in appearance at the 18-hour mark, with the kräusen on the high mash temperature beer staying fairly low with larger bubbles (right) while the low mash temperature kräusen was beginning to grow (left).

Sure enough, the low mash temperature batch (left) ended up making a mess about 24 hours into active fermentation. I swapped the airlock with a blowoff rig and left it on until the kräusen dropped a bit, maybe eight hours or so. The high mash temperature beer was tame throughout fermentation.

I took the first hydrometer measurement once signs of fermentation activity had waned, then confirmed it hadn’t changed the following day, the sixth day since brewing the beer. The 0.009 SG difference was initially pretty shocking to me though ultimately left me feeling confident such a highly discussed process component actually did what it’s purported to do.

I proceeded to cold crash, fine with gelatin, and package in kegs. To carbonate, I hit each keg with 40 PSI for 18 hours before purging and reducing to 13 PSI for serving. By the time I began to collect data the following weekend, both beers were carbonated and looking nice.


I began harvesting yeast from starters a few years ago after trying my hand at rinsing yeast . . . and hating it. Since then, I’ve taken yeast out as far as 15 generations without any noticeably negative impact on the finished beer (at least to me and my pals). I’ve heard a number of professional brewers talk about how they actually get the best performance out of their yeast, it “hit its stride,” at around the fourth through sixth generations. To be sure, nearly every beer I’ve done well with in competition has been fermented with harvested yeast. I’ve also been asked numerous times since posting about my yeast harvesting method if I’ve ever compared harvested yeast to a fresh vial. I hadn’t, until now.

Both starters showed signs of activity within eight hours. The vial starter is on the left, the harvested yeast is on the right. The kräusen in the harvested flask was significantly larger at this point, though the other one caught up soon after.

(Left: Harvested. Right: Vial)

The morning of brew day, I harvested a liter off of each starter (for future use) and split-off the portion of the harvested starter that would be used for the other beer.

For this experiment I chose to brew my own Munich helles recipe, splitting a 10-gallon (38-L) batch into two parts. I used White Labs WLP029 (German Ale/Kölsch) yeast. I made two yeast starters two days ahead of brew day — one from a vial of yeast, the other from harvested yeast.


To compare the differences between two beers made from the same wort and pitched with the same yeast strain, one from a fresh vial and the other a 4th generation strain harvested multiple times from prior starters.


Given the potentially subtle differences, I thought it would be best to make a lighter beer and settled on splitting a 10-gallon (38-L) batch of my 1.047 OG Munich Helles (you can find the recipe here: http://bru Unfortunately, I was forced to use German Pils malt in place of the Belgian Pils I usually use in my recipe on this brew day due to lack of availability.

I made separate starters for both yeasts about two days ahead of time, using a yeast calculator to determine starter sizes for both yeasts, including an additional liter for subsequent harvesting. I assumed a 100 billion initial cell count for the harvested starter and the prior date of harvest was used for production date.

A quick caveat before we go any further: The harvested starter was calculated to have slightly more than double the amount of cells as the vial starter due to the fact I was splitting that starter to use half in a batch of Märzen — I happened to have a big party planned that I needed beer for. I took great care to make sure the starter was well homogenized prior to being evenly split. This is something I’ve successfully done many times in the past.

Both starters showed signs of activity within eight hours. I measured the specific gravity for the first time a week after pitching the yeast, and again two days later (nine days after pitching the two yeasts).

The tasting commenced during a 4th of July party I held at my house in which many homebrewers attended. The beers had been on gas in my 38 °F (3 °C) keezer for exactly two weeks at this point. I collected data using an online survey tool (, which tasters received via text message just prior to evaluating the beers. Each beer was randomly given a name of a character from one of my favorite movies: Lloyd (fresh vial) and Harry (harvested). Tasters were instructed to take their time evaluating the beers in relative privacy just after arriving at my house, before drinking too much. With one exception, the tasters were unaware of the nature of the experiment and blind to which beers were represented by the character names. Once each taster completed the survey, they were asked not to discuss their experience with others who had yet to do the evaluation.

I ditched the triangle test component this time around. Besides being a pain and the most likely place where I could mess something up (by forgetting which beer was in which glass), it just didn’t seem to add much value to the experiment, so I skipped it.


Nine tasters evaluated the beers. The tasters ranged from homebrew club board members with years of brewing experience to a couple guys who typically drink Coors Light. Before getting into each taster’s subjective impressions, I’ll share some of the hard data:
• 67% believed Lloyd had the better appearance, no one claimed there was no difference
• 67% believed Harry had better aroma, 1 taster (11%) believed there was no difference
• 67% believed Lloyd had better flavor, no one claimed there was no difference
• 56% believed Lloyd had better mouthfeel, 2 tasters (22%) believed there was no difference
• 78 % said they preferred Lloyd, 1 person (11%) preferred Harry and 1 had no preference
• 44% accurately guessed which beer was fermented with the harvested yeast


According to the data collected in this experiment, there appeared to be a general preference for the beer fermented with a fresh vial as opposed to harvested yeast. Not only did this surprise me a bit, as I was certain this fourth generation yeast would far outperform its less experienced competitor, but it was initially a bit of a downer given the fact many of us homebrewers religiously harvest yeast from starters with the expectation of at least similar quality. As I pondered these results, going over in my mind whether I should stop encouraging folks to harvest from starters, I had to remind myself of a few things:
1. This is only one test that should (and will) be repeated numerous times in the future.
2. The “harvested” beer was still delicious and even preferred by some (myself included).
3. There are other potential factors at play, and I think more experimentation is needed to truly conclusively say whether fresh yeast is really best when homebrewing.

Moreover, when asked later, every taster who particiated in the experiment who reported a preference for Lloyd said the differences between the two beers weren’t strong enough to stop them from harvesting yeast from starters in their own homebrewing.

In the end, I think more experimentation is needed. This experiment seems to validate the subjective nature of perception and preference when it comes to tasting beer more than anything else. While the beer fermented with a fresh vial won the preferential pick from more folks, I would contend the comments of the tasters both during and after the evaluation validate the idea that delicious beer can be produced using harvested yeast as well — which of course we already know as most commercial brewers brew using harvested yeast! For more yeast experimenting, check out Ray Found’s pitching experiment at:

Once the wort was chilled to just above groundwater temperature, which was a balmy 74 °F (23 °C), I immediately filled both carboys, trying to get about the same amount of kettle trub into each one.

I then placed the carboys in the fermentation chamber (with the yeast starters — top right) and allowed them to chill down to my preferred pitching temperature of 56 °F (13 °C).

I decanted the starters at 5 am the following morning, approximately 12 hours after I placed the wort in the chamber. A simple observation revealed the yeast cakes at the bottom of each flask to be almost exactly the same in terms of thickness and color. Both of the yeasts were then pitched.

Both starters were then placed in a cool fermentation chamber where they would be left overnight to crash while the wort was chilling to my target pitch temperature. Brewing commenced later that afternoon, all went as expected.

I noticed the first signs of activity after about 13 hours, which is about what I expect when I ferment a batch with WLP029 (German Ale/Kölsch) at this cool of a temperature.

I was surprised to discover the beer pitched with the fresh vial becoming active prior to the beer with the harvested yeast, particularly given how different the starters were. Even after an additional 11 hours, 24 since the pitch, the harvested yeast was lagging behind the vial.

I found it somewhat odd that the Märzen pitched with the harvested yeast and having a very similar OG was fermenting more like the Helles pitched with the vial. It took 36 hours before the beer with the harvested yeast caught up with the others, at which point my anxiety dwindled and things seemed to proceed more as I expected.

On the fourth day, I began ramping the temperature up from 58 °F (14 °C) to 65 °F (18 °C) to encourage complete attenuation. Activity in both beers had decreased significantly by day six. I measured the specific gravity for the first time a week after pitching the yeast: Harvested was 1.013 SG, vial was 1.011 SG. I took a final SG measurement two days later and found the vial beer to be 1.010 SG while the harvested beer had dropped to 1.011 SG.


I’ve always been interested in the differences between pellet and whole leaf hops. Clearly both can be used successfully. For example, Sierra Nevada makes world famous beers utilizing only whole leaf hops, while many other commercial breweries tend to stick with pellets. As a homebrewer with fairly easy access to both pellet and leaf hops, I use both regularly. It seems to me that most brewers’ decisions whether to go with pellets or whole leaf generally has to do with storage and filtering considerations. However, for me an even more important question remained: Which form of hops make the best beer? From this question a dry hopping experiment was born.


To evaluate the impact of dry hopping a split-batch of the same homebrewed beer with pellet hops versus whole leaf hops.


I purchased a pound each of 2014 Centennial pellet and leaf hops from Hops Direct as soon as they became available. My thinking here was that sourcing the hops from a farm that grows and processes their own crop would increase the odds that both versions would be of similar quality and chemical makeup (i.e, alpha
acid %, oil levels, etc.). Moreover, I decided to stick with a single hop variety to keep things simple and not muddy the waters. Upon arrival, I gave the hops a quick smell test. I picked up a surprisingly strong lemon aroma from these hops with some subtle floral notes. The aroma from the pellet hops was significantly more subdued compared to the whole leaf, which smelled much stronger, brighter, and sweeter. The differences were fairly obvious, one that I definitely was not expecting since these hops came from the same exact source.
For the base beer, I used a Bell’s Two Hearted IPA clone based roughly on a recipe provided by Sean Terrill, which you can find on his blog site at:


In all, 14 people participated on the tasting panel, all of whom were provided no information about the nature of the experiment. Each participant received three samples of beer, two of which were dry hopped with pellets and one that was dry hopped with whole leaf hops. The tasting panel included three homebrewers, four BJCP certified judges, and a BJCP provisional judge.

Given the sample size, statistical significance would be achieved if 9 or more of the participants accurately distinguished the beer dry hopped with leaf from the two dry hopped with pellets. Of the 14 people on the tasting panel, 8 (57%) correctly selected the different beer sample. From a purely statistical standpoint, this does not conclusively prove there is a strong perceptible difference between a beer dry hopped with pellets compared to one dry hopped with whole leaf hops.

After making their triangle test selection, each taster was then asked about how confident they were in their selection. The responses here yielded some interesting results:
• Two participants indicated they were not very confident, and neither were correct
• Of six participants indicating they were somewhat confident, four were correct (67%)
• Of five participants indicating they were very confident, four were correct (80%)
• Of one participant indicating they were absolutely certain, none were correct

Extrapolating from this data, we can at the very least conclude that confidence is to some degree correlated with selection accuracy, which I found to be rather interesting.

There was nearly unanimous agreement among the eight correct participants that the beer dry hopped with whole leaf hops had a fresher, stronger, sweeter, and generally more pleasing aroma compared to the beer dry hopped with pellet hops; only one person described the aroma of the beer dry hopped with whole leaf as being “less hoppy.” The pellet hop beer was described as having a smoother and milder flavor, with one person saying they experienced far less hop flavor in it compared to the whole leaf beer.

My impressions: My initial experience couldn’t have been more different from the tasting panel. When I first triangle tested myself (served blindly by someone else), I perceived the beers as smelling strikingly different, making the correct choice obvious. But, I realized something interesting while analyzing the data that may provide a potential explanation for these results. The first four participants evaluated the beers within days of it being racked from the dry hop keg to the serving keg. They all chose correctly. At the time, this experiment seemed like an obvious slam dunk. Then life happened and I wasn’t able to administer the evaluation for about a week, during which the beers remained untouched in the kegerator. I finally cajoled a couple more beer drinking friends into participating and was stunned to discover they both selected the wrong beer. Out of curiosity, and for science of course, I sampled the beers side by side again. To my surprise, and despite my obvious bias, the perceived difference was nill. What was going on? Apparently, the nuances of dry hop aroma can fade far faster than I ever expected. I went on to collect additional data for this experiment at a Pacific Gravity Homebrew Club meeting the following week. Again, many had difficulty choosing which beer was different, and even those who chose correctly reported the differences as being very subtle. This was a result I had not expected and makes me wonder to what extent the additional plant matter from the whole leaf hops affects head retention.


The question I originally posed for this experiment was simple: Which form of hops are better for dry hopping, whole leaf or pellet hops? Based on the statistical data alone, it seems both contribute similar aromatic qualities when used for dry hopping. So, take your pick, it probably doesn’t matter.

However, my takeaway is slightly different. Given the fact the first few participants were easily able to distinguish between the two beers, I’m comfortable accepting that beers dry hopped with whole leaf hops will be noticeably more intense when they are fresh, while the intensity fades over time, eventually dropping to a level similar to that of a pellet dry hopped beer. This will definitely impact my decisions when it comes time to design recipes in the future, perhaps it will yours as well.

The finished beer would be evenly split between two “secondary” kegs and dry hopped separately. I wanted the hops to float freely in the keg and not be hindered by a hop bag. I repurposed two stainless steel mesh dry hoppers I had lying around to serve as keg hop blockers by drilling a hole in the top and attaching them to the end of each dip tube.

This brew day ended up becoming one of those times where everything went perfectly . . . wrong. It seemed the beer gods had it out for me. I undershot my mash temperature by 4 °F (2 °C), milled my grain fine enough to reduce the recirculating wort to a trickle, clogged my kettle hop filter while recirulating during the hop stand, spilled a bunch of wort, burnt my arm, overshot my OG by 0.017 points. I eventually chilled the wort to about 85 °F (29 °C), transferred it to my Corny keg fermentation vessel, and placed it in my modified chest freezer to finish chilling. It reached my target pitching temperature a couple hours later, at which point I proceeded to oxygenate the wort, and pitch the yeast.

The beer was fully attenuated by the following week, dropping to the expected FG of about 1.013.

The blockers worked perfectly. I immediately put the beers on tap and excitedly pulled a couple test samples to compare. The pellet dry hopped beer (right) was significantly more hazy upon first sample, while the beer dry hopped with whole leaf (left) was looking pretty good.

After sanitizing each keg, I measured out 60 grams (2 ozs.) each of leaf and pellet hops, adding them to their respective kegs. I then repeatedly pressurized and purged the empty kegs, a process intended to rid the keg of all oxygen, which I believe is crucial for hoppy styles like IPA.

Next, I transferred approximately 2.5 gallons (9.5 L) of beer to each keg using a closed transfer system, which is as simple as pressurizing the primary keg then using a “jumper” to connect and push the beer to another keg.

I allowed both beers to rest on the dry hop additions at room temperature for a week, leaving them attached to the CO2 to carbonate. When the time came, I sanitized two more empty kegs and transferred the finished beer into them, putting my makeshift blockers to the test for the first time.

There was nearly unanimous agreement among the eight correct participants that the beer dry hopped with whole leaf hops had a fresher, stronger, sweeter, and generally more pleasing aroma compared to the beer dry hopped with pellet hops.

A couple of the tasters noted something interesting that I had previously missed from my initial impressions — the head on the beer dry hopped with whole leaf hops dissipated slightly quicker than that of the beer dry hopped with pellets (whole leaf dry hopped beer on the left, pellet dry hopped beer on the right.)

Both beers cleared up rather nicely a few days later and looked essentially identical by data collection time. Left: Dry hopped with leaf. Right: Dry hopped with pellets)

Fourteen people participated in the tasting panel, all of whom were provided no information about the nature of the experiment. Each participant received three samples of beer, two of which were dry hopped with pellets and one that was dry hopped with whole leaf hops.

Issue: January-February 2016