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Since writing my last article, I have had the pleasure of using the Plastic BMB a few times. After a lot of thought on comparing the glass versus plastic, I think I have a good idea on which I prefer, why I feel this way, and the pros and cons of both.
First, I will start with the glass BMB.
Glass Pros:
  • Zero air permeation, just like any glass carboy
  • No chance of carryover taste from batch to batch
  • Nice harness makes moving and pouring a lot easier than traditional brew haulers
  • Can last a life time with proper care
Glass Cons:
  • Fragile
  • Defects in the glass
  • Lid cannot accommodate any sort of siphon or thief
  • Difficult to rest siphon hands free
  • Heavier than plastic, 6.5 gallon weighs 16lbs empty! That's about equal to carrying 2 extra gallons of beer.
  • Potential need for replacement gaskets. Although rare, it can still be a potential recurring cost.
As you can see, there are more cons than pros in my eyes. I do love to use glass, but I have some concerns with these fermentors in particular. The imperfections in the glass concern me, I constantly find myself checking for stress cracks around the defects.

As a primary, I see no need to go with the glass version over plastic. Keeping oxygen out at this stage is very easy, and air permeation isn't really an issue. The lack of ability to siphon with the lid on is really off putting after using the plastic BMBs. Not having a punted bottom for the siphon to rest on doesn't help either. You may not notice a difference having never had these features, but I am having a hard time going back.
However, as a secondary, the glass version still proves invaluable. I make a lot of beers that benefit from long term aging. I know that the air permeation of PET plastic is supposed to be very low, but it isn't nonexistent. Either way, I trust glass, or a keg, for long-term aging.
Also, something to consider is the size of both.

These are the 6.5 gallon sizes. As you can see, the plastic version is noticeably taller than its glass counterpart. Plastic coming in at 23 inches and glass coming in at 17.5 inches. The 5-gallon versions have similar differences. Plastic coming in at 22 inches and the glass coming in at 16 inches. All of these measurements do not include airlocks of course. Something to consider along with your fermentation chamber size before you purchase either one. That being said the 10-inch footprint of the plastic is significantly smaller than the glass at almost 18 inches.
Now on to plastic. Not being a fan of buckets, I never thought I would like plastic so much.
Plastic Pros:
  • Super light (4-lbs. for the 6.5 gallon)
  • Dual port lid (optional)
  • Punted bottom
  • Volume markings
  • Much easier racking
Plastic Cons:
  • Same flexing problem as other plastic carboys
  • Lid ring seems to work itself off unless tightened down very hard
  • Texture on the anti-flex ribs like to hold onto when cleaning
  • Air permeation
Biased or not, I definitely feel there are more pros than cons to the plastic version. As long as you aren't doing any long-term aging, you can't go wrong with the plastic version of the Big Mouths.
The biggest advantage in my opinion is a combination of the dual port lid and the punted bottom. I'll start with the former.

The dual port lid is amazing. I like taking samples as my beer ferments, and while it's conditioning. I have all but permanently stored the single port lid. Being able to sample and rack without removing the lid is easily my favorite feature. That in combination with the punted bottom really takes the ease of use to a whole other level.

The punted bottom is also amazing. I always attach my tubing to the racking cane after I put the siphon into the wort. So, I will put the auto siphon together, and find the punted bottom and just let the siphon rest in that indent, while I attach the tubing and proceed to siphon. Can't get much easier.

As you can see, there isn't much left after siphoning. I got this much out of it and did not move the siphon an inch. However, I do see a potential issue with this, maybe with low hop lower gravity beers. I had plenty of trub in this beer, so I only lost about 1/8 of a gallon. If there were less trub I could see you potentially losing up to of a gallon.
All that being said, I still would refrain from aging anything long term in these. PET plastic is supposedly still air permeable. Although it may be to a lesser degree, I still wouldn't risk it on a brew I intend to age in the fermentor.
I don't know if I would say one is better than the other. I prefer each for specific purposes. However, I will help you make the best decision for your specific needs or situation.

Reasons to consider plastic

  • Much lighter, at only 4lbs for the 6.5 gallon
  • Smaller footprint, if that is valuable in your fermentation setup
  • Dual ported lid makes just about everything easier
  • Punted bottom in conjunction with the lid is amazing
  • Virtually indestructible
Reasons to consider glass
  • Does not permeate air
  • Preferred material for long term aging
  • Short in stature, if that is valuable in your fermentation setup
  • Lasts a lifetime
Considering all this, I hope I have helped you decide which is best for you. I have used both, and would say without a doubt both are great buys. The ability to reach your arm inside the carboy and clean is revolutionary. I love them both and wouldn't turn either down. I got all of mine from Northern Brewer, they have always been great to me and the flat rate shipping is awesome.
Thanks for reading. Cheers!
Check out my new blog! Fountain City Brewery. Brought to life by my love for brewing, my hometown Kansas City, and writing for homebrewtalk!
Supposed to say "loss of up to 1/4 of a gallon" sorry! Most of my beers have plenty of yeast/trub that make it to the fermentor so not a concern for me.
Also, thanks for everyone visiting my blog :). It will get better, ust started it up a couple weeks ago. Gonna get some recipes up there and brewing techniques etc.
I wonder if anyone should consider plastic given the estrogenic properties of the material. The biopharmaceutical companies I work with have done leaching studies that prove to them that there is leaching from plastics and there are further studies that show ALL plastics appear to release estrogen into contents that come in contact with wetted surfaces. Is this something that concerns other home brewers?
I think it would concern be more if the beer were in contact with it longer. I've seen some articles about that situation in general, not necessarily to PET plastic, but can't find anything more specific than it can leech that kind of stuff.
If the information were more definitive, and I were putting warm liquids in it, then I would be more concerned. It's in the back of my mind, but it won't stop me from using them. Until I finally get a stainless steel vessel that is.
Only thing I don't like about plastic better bottle (I know this is about the big mouth)is when you go to move it, it inevitably sucks down some (if not all if your not careful) of the starsan in the lock. As long as you don't have to move the fermenter a lot, it works perfect. Of course I don't have a brew hauler so there is that. Anyone else have this problem, and for those that don't is it due to the brew hauler/harness? Also,I wouldn't think you'd have to worry about this with the thicker plastic of the Speidel fermenters if anyone with one of those wants to chime in.
@kcmobrewer beer ferments and is in contact with plastic at the same temperatures and for the same length of time as biotech fermentations. The leaching studies are valid and the estrogenic issues are real. But, it is almost impossible to get away from plastic: sports drinks, soda, beer in cans, gallon milk jugs, etc. all contribute to spreading estrogen into foods we consume. Like you, I choose stainless (sanke kegs) if given the choice. But, a little more plastic probably won't tip many people over the edge.
We brewers are so fussy about things (or many of us appear to be!) that compromising on our fermenter seems a little out of character for us!
Yeah I agree with all that stuff about the plastic, hard to get away from it though unfortunately. At least these are designed for brewing. It would really make me nervous using the huge plastic conicals that are primarily used for other types of chemicals. They're getting pretty popular these days, but I am steering clear.
@zeptrey I put solid stoppers in place of the airlocks when I move these so nothing gets sucked in. Works like a charm. If you don't do that you will have the same issue as the past better bottles. A little less so with these new ones, as they have those "anti flex" ribs, but they still flex. Especially the 6.5 gallon. The 5 gallon is noticeably more rigid.
I use plastic 6 and 6.5 for primary and use 5 gallon glass for secondary and long term aging. Seems to me that this is the best way to go. You go through primaries quicker and you don't move secondaries around as much (carrying from the garage to the basement)
I'd love to see them make a 3 gallon version of either or both for smaller batches. Good comparison. Thanks
About the suck back of the star-san....If you don't have a brew hauler, then just use some old cheap milk crates.
I agree. I would love to see a 3 gallon version of the plastic BMBs.
There is one additional con with plastic over glass and this may not affect brewers as much as wine makers but wine makers tend to want to remove as much CO2 as possible from wine and we often use a vacuum pump for that purpose. A glass carboy does not deform under 20 inches of vacuum. Plastic does.
Vacuum pumps are also often used rather than siphons to rack wine and to bottle. The advantage of a vacuum is that you do not need to lift a 5 or 6 gallon carboy to a height and indeed you can transfer wine without the help of gravity. This means that older wine makers and weaker wine makers are still able to engage in their passion.
I like my Glass Big Mouth 6.5 Gallon...That said, I love glass fermenters.
...as far as fitting a thief?
I can fit my stainless "turkey baster" style thief in the opening without question.
My only problem is figuring out a way to do my CO2 pressurized transfer to my cornie.... It is easy with my standard glass carboys using the orange 2 pronged caps...
I am currently working on a screw on adapter that will allow a stainless racking cane and CO2 attachment for transfer to my cornie from the 6.5 wide mouth glass carboy...
I'm finalizing the adapter in my CAD software now and should have a 3D printed working part in a few weeks...
I have one of each ... a 6.5 gal glass and a 6.5 gal plastic.
So far, I love them both but the glass one is a bit much for me to lift and place into my chest freezer ferm chamber by my self (I'm an old fart). I have started to use the plastic one for primary in the chest freezer chamber and the glass one in the converted refrigerator chamber. I don't often use a secondary, but when I do a 5 gal glass carboy is the choice.
The punted bottom in the plastic carboy is a definite plus as it is not necessary to use a 2X4 to tilt the carboy when siphoning. Oh ... and I do use milk crates to trolley them on a movers dolly from the brew site to the ferm chambers.
I too have one of each...I currently have a batch going in each one. I love them both...however I seem to be having an issue getting the lid for the plastic one to seal good. Had to really get a hold of the lid and twist hard to stop the excess leaking and get bubbler action. I do like the design of the lid for the plastic one better just wish it would seal better. For those of you that are doubting using plastic...I just started brewing in January...I have already had TWO glass carboys blow the bottoms off. Very glad they were just sitting on the floor...but I still got cut...and had hours of cleaning for both. It seems there has been some garbage quality Carboys entering the market as of late...and I had two of them. Never again...I recently ordered two more plastic Bubbler Carboys...and will be putting my glass in the garage. The only glass I will continue to use is the glass BIG mouth...
I only use my plastic when I am out of glass carboys or use it for primary, It has more room and i can use 10 gall bucket for primery,6 gal for secondary and 5 gal for 3rd racking. that way i avoid topping up.
Regarding estrogen and PET:
Thank you for the write up, I've been going back and forth on both options from the moment I saw them advertised on NB. It was nice to see the options available on the plastic version. I have always fermented in glass carboys, but I will be picking up a few plastic BMBs to use as my new primaries.
I just got 2 of the PET BMB's for 10 Gal batches, and so far I love them. Also I love the ability to top crop without a turkey baster.
I didn't realize the glass version has such a restrictive lid. Seems like it would be easy for them to find someone to manufacture them. I work at a place that builds plastic molds and I am positive that a small injection mold would not be very expensive to build.
I could see myself machining a lid or two out of food grade plastic for my own use. It would not be cost effective to mill them in bulk, compared to molding them (I'm guessing a single cavity mold could operate with about a 30 second cycle time and could be run unattended for hours.)
I need to set up a reminder to clean up my tools in the garage and get my blonde ale in the plastic bubbler for a trial run.
Is there any chance these don't old smells like a bucket? I've only tried plastic a few times and hated every bit of it. Couldn't see anything and worse, it held smells for ever, literally forever. I had a bucket smell like a fresh ipa a brewed for months after washing 3 times in pbw. It's used for grains now... I had another I tried a mead in. It has smelled like strawberries for over a year after it being retired as a fermenter. I use it to mix up nutrients and water hop plants now. After a year, it still smells like that mead.
First I bought the glass one. I loved everything about it but the weight. Then I saw the plastic version and jumped right on it. BUT I can't get the plastic BMB to seal good. It is driving me nuts to the point of me ordering another glass one.
Does anyone elses have a rough mold point at the punted bottom?
Thank you for the review.
I also wanted to comment on the estrogen leaking from plastic comments.
There are very few studies that demonstrate this and most of them are not reliable repeatable or they are on such a small scale (small sample size) and poorly designed that they should not be taken seriously at this point until more evidence suggests this to be a possible method of hormone contamination.
What is likely happening is that as our analytical methods improve and we are able to detect stuff in smaller and smaller concentrations, we are going to be able to find what ever we are looking for. If you look hard enough you will find whatever you're looking for in such a small concentration. For example one of those studies cited concentrations in the nanograms per liter concentration that is less then one part per billion! I believe what is going on is that these compounds are being detected in the water in which the samples are made. That is definitely something to be concerned with as our water sources , especially those that are treated and or pumped from aquifers are contaminated by human waste both fecal and urinary that is as a result of widespread oral contraceptive use...now that is a big problem and something I have studied.
I don't want to be dismissive of these claims but we can't rush to judgment and I was surprised to see the lack of disagreement when one person asserted this premise. There are many things to be fearful of for example microwaving or re-heating your meal in the Styrofoam container it came in, too many things to worry about but at this point in time estrogen coming from plastic is not one of them. You'll get more estrogenic compounds from soy milk and soy products but again, not in enough concentration to likely cause a ligand response and for example demasculinate a boy who drinks soy milk exclusively(that said I dont let my kids have soy milk!).
So sorry for the rant and I apologize for most or any typos if you come across them as this was mainly transcribed by Siri :)