Author: Andy Carter
Every homebrewer has to start somewhere, and for most it usually involves picking up a beginner’s kit that comes with a small kettle, spoon, hydrometer, some hop bags, and of course, a food-grade plastic fermentation bucket. Cheap, effective, and easy to clean, plastic buckets are made of high-density polyethylene (HDPE) and remain the fermenter of choice for some, particularly those who prefer the simpler side of brewing.
However, despite their general convenience, many brewers end up relying on other types of fermenters due to certain issues with plastic buckets, namely oxygen permeability and how easily they scratch. While glass carboys were once the most common alternative, less expensive plastic carboys have grown in popularity over the years. Made of polyethylene terephthalate (PET), these newer vessels are lighter in weight than glass while offering reduced oxygen permeability than plastic buckets. Moreover, PET is a bit harder than HDPE and thus more resistant to scratches that can harbor beer spoilage microbes.
Plastic buckets are certainly the cheapest fermentation vessel option, though PET carboys have become the mainstay in my fermenter corral due primarily to concerns of post-fermentation oxygen exposure—that large diameter opening is a nice place for air to come in when taking hydrometer samples and racking to kegs. With one past xBmt suggesting tasters could tell apart an IPA fermented in a plastic bucket from one fermented in a PET carboy, I was curious to test it out again for myself.
| PURPOSE |
To evaluate the differences between a Pale Ale fermented in a HDPE bucket and one fermented in a PET carboy.
| METHODS |
Given concerns of oxygen permeability, I opted to brew a Pale Ale for this xBmt, the recipe of which was lightly inspired by Sierra Nevada Pale Ale.
Beginner’s Luck
Recipe Details
| Batch Size | Boil Time | IBU | SRM | Est. OG | Est. FG | ABV |
|---|---|---|---|---|---|---|
| 5.5 gal | 60 min | 37.3 IBUs | 9.9 SRM | 1.055 | 1.012 | 5.6 % |
| Actuals | 1.055 | 1.005 | 6.6 % | |||
Fermentables
| Name | Amount | % |
|---|---|---|
| Pale Malt (2 Row) US | 10 lbs | 90.91 |
| Caramel/Crystal Malt - 80L | 1 lbs | 9.09 |
Hops
| Name | Amount | Time | Use | Form | Alpha % |
|---|---|---|---|---|---|
| Sterling | 20 g | 60 min | Boil | Pellet | 8.6 |
| Sterling | 20 g | 20 min | Boil | Pellet | 8.6 |
| Sterling | 43 g | 5 min | Boil | Pellet | 8.6 |
Notes
| Water Profile: Ca 43 | Mg 5 | Na 8 | SO4 65 | Cl 44 |
Download
| Download this recipe's BeerXML file |
I started my brew day by adding identical volumes of RO water to separate BrewZilla units, adjusting each to my desired mineral profile, then setting the controller to heat it up.
While waiting on the water to warm, I weighed out and milled two identical sets of the grain.
Once the water for each batch was properly heated, I incorporated the grains then checked to make sure they hit my target mash temperature of 150°F/66°C.
While the mashes were resting, I prepared the kettle hop additions.
Once each 60 minute mash was complete, I removed the grains and sparged to collect the same pre-boil volume.
Following each 60 minute boil, I ran the wort through my chiller while being pumped to either a plastic bucket or PET carboy.
Refractometer readings showed both worts hit the same target OG.
I placed the filled fermenters next to each other in my chamber and let them finish chilling to my desired fermentation temperature of 66°F/19°C for a few hours before returning to pitch a single pouch of Imperial Yeast A07 Flagship into each.
After 5 days of active fermentation, I raised the temperature to 70°F/21°C and let them sit for another week before taking hydrometer measurements confirming both reached the same FG.
With the beers done fermenting, I racked them to sanitized kegs, doing my best to keep things as equal as possible.
The filled kegs were placed in my keezer and left on gas for 3 weeks before I began evaluating them.
| RESULTS |
Due to social distancing practices as a result of the COVID-19 pandemic, data for this xBmt was unable to be collected in our typical manner. As such, temporary adaptations were made involving the author completing multiple semi-blind triangle tests in as unbiased a way as possible.
Utilizing 4 opaque cups of the same color where 2 were inconspicuously marked, one set was filled with the beer fermented in a HDPE bucket while the other set was filled with the beer fermented in a PET carboy. For each triangle test, 3 of the 4 cups were indiscriminately selected, thus randomizing which beer was the unique sample for each trial. Following each attempt, I noted whether I was correct in identifying the unique sample. Out of the 10 semi-blind triangle tests I completed, I needed to identify the unique sample at least 7 times (p<0.05) in order to reach statistical significance, though I did so just 5 times (p=0.21), indicating my inability to reliably distinguish a Pale Ale fermented in a plastic bucket from one fermented in a PET carboy.
When packaging these beers, I could have sworn the one fermented in a bucket had stronger aromas of yeast and fruity esters, whereas the batch fermented in a PET carboy had more spice and citrus. However, once kegged and conditioned, any differences I thought I perceived had disappeared, the beers were identical in every way. I felt the citrusy bouquet from the Sterling hops paired well with the richer specialty malt character in this beer, which had a solid bitterness balanced by a grainy sweetness. A bit more complex than the typical Pale Ale, but still clean and very drinkable!
| DISCUSSION |
There are number of factors that go into deciding what type of fermentation vessel best suites a brewer’s needs, though for most beginners, the decision is made for them—a plastic bucket. As one becomes more obsessed with crafting the finest beer possible, they’ll eventually hear of the ills of fermenting in such vessels and feel compelled to consider alternatives, a popular choice being PET carboys, which purportedly reduce the risks of oxidation and contamination. My inability to reliably distinguish a Pale Ale fermented in a plastic bucket from one fermented in a PET carboy suggests fermenter type had little if any perceptible impact.
Seeing as these findings contradict those from a prior xBmt where tasters could tell apart beers fermented in either type of vessel, it’s worth considering possible explanations. While I’m inclined to point to the fact the initial xBmt had a sample size of just 10 participants, all of them were blind to the variable, whereas I as the single participant was completely aware of everything about these beers. Presuming the difference perceived in the first xBmt was real, I wonder if it wasn’t in some way a function of flavor carryover from the many batches of beer that had previously been fermented in the bucket. It’s also possible any differences between the beers were below my personal flavor threshold and, if served to a group of participants, a significant number would have performed better on the triangle test.
I adopted PET carboys as my fermenter of choice for various reasons, and while the results of this xBmt won’t convince me to give them up, they did increase my confidence in using HDPE vessels for fermentation. As someone who occasionally ages beer the primary fermenter, I maintain a level of concern about the oxygen ingress that can occur when using buckets for such a purpose and view that as a good variable to explore in the future.
If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!
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13 thoughts on “exBEERiment | Fermentation Vessel: HDPE Bucket vs. PET Carboy In A Pale Ale”
Nice write up. There’s also another possible explanation that comes to mind that speaks to the lack of a perceptible difference…
I noticed in the photo you did an open transfer from ferm vessel to keg, and in the write up you said it was a “sanitized keg” but not a “CO2 purged and sanitized keg”. Both of those factors add lots of cold side oxidation to a beer and make a difference in the final product.
Since a factor that would likely cause flavor differences between the two vessel types is oxygen exposure, any small differences driven by the choice of fermentation vessel may have been wiped out by equal amounts of heavy cold side oxidation when kegging.
I can clarify that: it is “CO2 purged and sanitized keg.” My process is to always fill the keg with StarSan, empty it with CO2, and rack into that keg.
An neipa would be an interesting one to try this experiment on.
Or a dry hopped beer
We always ferment in stainless conical vessels. Plastic buckets will absorb the flavors / aromas of the beers over time, and have an impact on beer flavor. Buckets will work, but best to discard them frequently as they pick up flavors readily.
It would be nice to see a comparison between plastic buckets and stainless fermenting vessels.
Interesting exbeeriment.
I would be curious to know how much oxygen enters through the walls over 3 weeks compared to how much gets in while opening the bucket to take an sample.
I have admittedly nothing to back it up but instinctively I would say that: opening the lid to take a hydrometer sample in a bucket > opening the lid in a carboy > oxygen ingress through the walls of a bucket > oxygen ingress through the wall of a carboy.
Even though ultimately only detection from the pallet counts, it could be interesting to quantify all these variables. They could be really close or they could be off by several orders of magnitude.
Then if you guys can get a hold of a DO meter you can even do an exbeeriment with 2 close-fermented beers (fermented in kegs) where one has been infused with specific amounts of oxygen via the gas post post fermentation.
Actually, I do have an anecdotal piece of evidence to back it up. The first batch that I kegged was fermented in 2 vessels (10 gal total). One in a bucket and one in a big mouth bubbler (plastic). I left the bucket undisturbed the whole time and only opened the big mouth bubbler to take samples (It was my first lager and I “had” to open it up 4-5 times to follow the fermentation… I only opened the stopper though, not the whole lid). The one that was fermented in the big mouth bubbler and opened a few times showed signs of oxidation nearly a month before the bucket.
This exactly! The amount of oxygen ingress when either opening a lid, or removing an airlock to sample or dry hop is surely orders of magnitude higher than any leeching occrring through plastic. Is there any data / evidence to show exactly how much o2 leeches through plastic over say, a decade? A century? Really? My beer is usually in and out in 3-4 weeks. Better chance i get o2 ingress around my top and airlock seals than sucking through plastics in that time. Glass or stainless versus any plastic fernentation vessel would have probably provided an interesting result.
Is that a big color difference at the hydrometer samples?
I think this is a lighting issue where I took the photo, and not an actual color difference. I could not perceive a color difference in the glasses.
They were both fermented in plastic. Plastic is permeable. Yes, different degrees, but still permeable. I’m not surprised there’s no noticeable difference. Rather than debate degrees of acceptable oxygen infusion I feel it’s just best to stick with either glass or stainless.
Another experiment rather showing me that the difference, if any, is tolerable, and that, as far as my limited process is concerned, nothing to worry about. KISS policy is what makes the hobby worth while IMHO.
My real concern would be what i am reading about discernible flavours being trapped / absorbed in plastics, over a period of time, and passed on to subsequent beers. Does this also absorption preclude any cursory metabisulphate/sterilising rinse, or is it yet another in a long line of brewing “traditions”, designed to make people buy more expensive gear?
Again, not denying flvours trapped in plastic as being possible, but what negative/positive impact could such retained flavour impart on subsequent beer?
I think a better test would have been glass or stainless vessel vs the old plastic bucket….. a really old bucket used multiple times at that…… and then see how it affected the taste. Now that would be interesting.
Sorry if this was answered elsewhere, but is it possible that you would have had different results if you first had pre-identified a sample of each beer to get a taste profile in your head prior to doing the blind tasting?