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BIAB question

Hello all,

I need some opinions on BIAB. Here is the reason. I understand the process of it and I was telling one of my friends about it because I thought it would be a nice easy way for him to break into all grain brewing. I told him I bought some, what I seem to remember was, polyester to use as the “bag”. Right there my friend flipped out on me. He told me that polyester contains carcinogens and is extremely dangerous at higher temperatures like in a boil. I told him he is full of you know what as I have read dozens and dozens and dozens of postings about BIAB and not one single time has anything about ANY dangers come up. Now I know when it comes to home brewing and I know you are all as safe as humanly possible. You guys have been brewing for decades and he has never brewed once. So I ask in all honesty does he have any kind of a claim? Any scientific proof either way? Let me know some thoughts. Thank you.


This page lists several components of polyester as carcinogenic, but doesn’t have any info about polyester itself. And let me point out that you won’t (hopefully!) be boiling the grain in the bag. Theoretically, it won’t get much hotter than about 160F.

Use nylon paint-strainer bags and have no worries at mash temps. I recently taught a friend the method and she’s making really good beer with it - only need a big kettle and 2-3 5-gal bags and you’re good to go.

I think it depends on what type of polyester it is as well. Those turkey roasting bags are made from polyester, and withstand temps much higher than boiling. Just make sure it is designed for brewing temps and it should be perfectly OK. Sometimes people confuse toxic chemicals used to manufacture a product with the product itself.

I’ve always heard to use nylon

[quote=“Iceman6409”]Hello all,
He told me that polyester contains carcinogens and is extremely dangerous at higher temperatures like in a boil.

First, a “poly” “ester” is many ester molecules in a chain. It is a generic term; polyesters can be composed of different types. Polyethylene terephthalate (PET) is a polyester and is commonly used in the food & beverage industry.

PET may release acetaldehyde which is a listed toxic, during thermal decomposition, but that is usually during in the neighborhood of 400 deg F, needed to melt plastic (even then, the amount of off-gas is very small).

Hey Shadetree are you suggesting to use a few paint bags? My scenario would be this for him. 9 gallon kettle. Add x amount of water and bring to desired mash temp. Let’s say 170 or whatever. Then you would essentially divide the grain bill into a few paint bags and drop into the water? I kind of like that idea to be honest. Does anyone else do it this way or see any issues in a BIAB method like this?

Up to 5# per 5-gallon paintbag works well for me - room enough to stir the grain and keeps the weight in the 10# range when you lift them out of the kettle to drain.

So you put 2-3 of these bags is a rectangular cooler? Do you tie them?

Do you mash, lift, drain, sparge, lift, drain?

[edit]I guess you don’t tie them if you stir them, so how do you keep it all together?

Doing this in a kettle, not a cooler, in order to keep it as simple as possible, but it would work in a cooler if you didn’t want to convert it with a manifold). I clamp the bags closed, then shut the lid with the clamp hanging outside, wrap the kettle with blankets. Since the idea is to do this with only one vessel, there is no sparging, just lift the grain out and allow it to drain a little. Efficiency is in the 60-70% range. But if you were using a cooler, you could heat some water in the kettle and dunk the grain bags, stir, and remove for a sparge, then drain the cooler to the kettle.

And this is pretty much how you do all your batches? If so, I am encouraged as that is how I do my partial mashes, just a a little bigger scale.

I use MIAB for anything less than a 5-gal batch and use a 9-gal kettle, but not for anything larger - much easier to use a cooler mashtun rather than messing with multiple bags of grain.

What material do you use? The paint bags? You put a couple of paint bags in a mash tun?

See post #3 above…

Why has this thread gone past Denny’s post? There’s NO boiling of bag in BIAB. End of discussion. :wink: Geeeze.


All due respect Stormy but my friend is flipping out because he believes that there are carcinogens in the polyester that I may or may not have used to mash in. The fact is I can’t remember for sure what material I have but it never got boiled. I only used it once in a picnic cooler mash tun.

So my only question that I am trying to find out is IF there are carcinogens in polyester and if so when would they become dangerous. So far it appears that there is not much danger at all until a temperature of about 400F according to a previous post. Obviously if that is true then there is no issue, except to my friend of course who at the age of 38 decided to have a colonoscopy because he was convinced he had cancer. How he “knew” he had cancer is a big mystery to me but he is also a HUGE conspiracy theorist too. So all in all all I care about is finding out if there is any danger to using polyester bags for BIAB. If someone could tell me definitively yes or no that would be hugely appreciated. And thank you all for the good information to this point :slight_smile:

You probably need to ask scientists instead of homebrewers.

I would just skip the BIAB and build Denny’s cooler mash tun. I just dug out a cooler we never used and spent maybe 15$ and I was batch sparging in not time. Check out his web site.

A search of Pub Med does not bring up any studies showing the release of carcinogens from Polyester (and it looks like quite a few people use polyester mesh for BIAB).
The most relevant papers seem to be these;
( the only time significant amounts of toxins were released from fabrics was when they were burned, and acrylic was worse than polyester due to the formation of cyanide during burning.
( Polypropylene and several other materials have been used as surgical implants for things like hernia repair, etc for many years and there are no reports of increased cancer risk in patients with polypropylene implants.

I think your friend is being paranoid, and if he really believes this stuff, you are probably not going to convince him otherwise. I guess you won’t have to worry about him drinking all your beer though. :wink:

Buy a package of nylon paintbags and tell him you figured it out, then show him the packaging and be done with it. :wink:

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