The lazy, hazy days of summer (beers).

Or: Why those tasty, tasty New England IPAs are legit cloudy – mostly.

There has been a surge lately in the number of beers being sold that are, how shall we say it…. less than clear in their visual appearance. For some styles, this is, of course, historically accurate and fully appropriate. Think Bavarian hefeweizen, or Belgian wit.

A nice, traditional hazy beer. (

For most other styles, a hazy beer is considered a fault and a mark of an improperly crafted beer. Of late, it seems that idea is being thrown by the wayside – maybe for the better and maybe not.

So, why has “bright” beer historically been a mark of quality? Why is haze a suggestion of a problem with the brewing process? And, importantly, why might some of the new hazy beers like the New England IPA be able to thumb their nose at the notion of clarity being an indicator of quality and be (mostly) ‘right’ about it?

Well, to find out, let’s talk about the causes of haze in beer. Surprisingly, there aren’t that many. You’ve got basically 3 categories of haze formers:

1) Biologicals: These would be yeast (think hefeweizen again) and bacteria (think infected beer or some barrel aged beers – though the latter should clarify due to the long aging times).

Electron micrograph of typical brewing yeast/ (






An electron micrograph of a common haze-forming spoilage bacteria, Lactobacillus. (








2) Processing materials: This includes fining/clarifying agents, dust, specks of paper/glass/metal from the packaging line.1 That sounds somewhere between unappetizing and flat-out scary! Have no fear, if these are there (which is uncommon, but not unheard of), they are microscopic in size and present no risks when consumed.

Microscopic flecks of label, glass, and aluminum from the packaging line. (Ref 1)

3) Chemicals: A host of compounds naturally present in the brewing process, which include proteins, polyphenols, large unfermentable sugars, and byproducts of yeast metabolism.


This is an unfermentable sugar called ‘maltotetraose’. It can’t pass across the cell membrane, so yeast cannot consume it. It stays in your beer and contributes to body and residual sweetness.


Yeast are only a problem if a brewer uses the wrong strain (such as a hefeweizen yeast in a pilsner) for some unfathomable reason, or if there is another fault in their brewing process that stresses the yeast because of the presence or absence of certain chemical species (too little calcium or too many unfermentable sugars, for example). Infection, as I have mentioned before, is a rare thing in any quality brew operation, so let’s leave the bacteria out of this as well.

Processing materials are very rarely a problem, as modern packaging and filtration equipment is so good, it eliminates this stuff pretty well. When it doesn’t, it generally fails spectacularly. An example might be a leak in a filter that lets the filter media through. Brewers won’t even consider packaging and releasing that beer. OK, well, they might – for a second. But once they stop swearing and/or crying, their better instincts will prevail. So, this category is seldom, if ever, a problem – and certainly not one you would easily detect by eye.

Thus, that leaves us with category 3. Those nefarious ‘chemicals’ (insert scary music here…) that are oft demonized by folks who fear what they cannot pronounce.

What I’d like to do today is take you on a tour of a few of the chemical compounds that arise in the brewing process and talk about why/how they cause haze and why/how that is usually an indicator of problems in the brewing process. This will also explain why new styles like the New England IPA can legitimately claim (most of the time!) that the haze in their beer is not a fault and, instead, is a ‘feature’, as those in the software world like to say when confronted with unanticipated issues in their code.

While I wander through this rogues gallery of compounds, I’ll name them and show you some chemical structures, just because that’s the way I think about them. But, fear not, there will be no test at the end of this, and the names and structures are not that important, so feel free to ignore the structures and rename the compounds anything you’d like that will help you think about what they do.

OK, then, we’re off!

Haze forming Rogue #1: Polyphenols

Phenol = planar 6 carbon ring with a -OH group hanging off it.








Poly = many. Hence, polyphenol. This Latin stuff is not so hard after all!










Polyphenols come from two major places in the brewing process. The first is the husk of the malted barley kernels. These compounds are astringent in nature and are not desired in beer under any circumstances. When they show up, they make the beer have a chalky, drying mouthfeel. If you’ve ever had a beer and at the end of a taste, it feels like your tongue is suddenly sticking to your palate, you’ve just experienced astringency. Or, perhaps you’ve had an unripe banana or left too much of the pith/peel from a banana or orange on the fruit itself? Then you have experienced this.

The polyphenols cause this sensation because they bind to and sequester the proteins in your saliva that lubricate your mouth. Hence, everything gets ‘tacky’ and dry in there.

In the brewing process, if the brewer tries to extract too much sugar from their malt, beats up the husks while milling the grain, or lets the mash pH get too high, polyphenols will be extracted and it will be astringency city. What’s worse, this problem is compounded if acetaldehyde is present in the beer.

Acetaldehyde. Poorly fermented beer result in this stuff which tastes like green apples.








Acetaldehyde is a small molecule that tastes like green apple and occurs if the yeast fermenting the beer were not healthy, not numerous enough, or subjected to temperatures too high or too low during fermentation. The acetaldehyde will react with the polyphenols and amplify the astringency effect of them.2

This is why astringency is considered a fault and why polyphenol-derived haze is often a visual indicator that you’re going to have a rough ride ahead if you sample a beer.

On the other hand, the second place that polyphenols come from is our beloved hops – most specifically those used for aroma. Doubly importantly, the hops used in dry hopping can contribute hugely to the polyphenol content of the beer if there are large amounts and if they are left in the beer for over a week.

The important distinction here, though is that these polyphenols are just cousins of the ones from the grain husks. These polyphenols contribute to the perceived bitterness of a beer and not much to its astringency. (Just as an aside, bitterness is a flavor, astringency is part of mouthfeel.) Hence, big, nasty, sticky dry hopped IPAs are often cloudy because of the hop-derived polyphenols. Usually. However, these are limited to appearing only when the beer is very cold – hence the term ‘chill haze’.

In this context, then, polyphenol-derived haze may not be a ‘fault’ in the brewing process, but may be a feature that comes along with the enormous late additions of hops. It can still indicate problems if the chill haze does not dissipate when the beer warms. That points to dry hopped beers that have been left too long on the hops, which can result in permanent haze from those hope polyhenols. So, this haze usually does not signal a rough ride ahead for the drinker, but rather an aroma and flavor bomb coming your way.

Haze forming Rogue #2: Calcium

(No picture here, sorry. Calcium ions are about as boring ‘looking’ as you can get. It’s just a tiny, submicroscopic sphere.)

Calcium is simply an elemental ion that shows up in beer both because it is in malt at low levels and brewing water at variable levels, depending on how much city water your local brewery uses and how much distilled water (water treated by reverse osmosis, really) they use. Lack of calcium is a haze former because it is an important ion for the process of yeast flocculation. Flocculation is the process by which yeast clump together and drop out of solution at the end of a fermentation. If a beer has too little calcium in it, then that process is interrupted and the yeast tend to stay in solution longer.

Lack of calcium also inhibits proper conversion of starches into sugars during the mash process and impacts yeast health as well. So, low calcium can cause flavor problems like under-attenuated beer (beer that’s overly sweet) and beer that has various off-flavors because the yeast were stressed during fermentation. Again, the signal that this might be a problem in your beer is haze – primarily due to suspended yeast at the end of the fermentation.

Haze forming Rogue #3: Residual sugars

This ties right into the calcium problem. If you have low calcium in the wort you made your beer from, then the final beer will be under-attenuated. If that happens, the sugars left over can bind to the surface of the yeast and interfere with flocculation. Once again, yeast haze!

Now, low calcium can cause residual sugar problems in a beer, but high gravity wort can do this too. Normally there are small amounts of sugars in wort that yeast cannot ferment. These include high molecular weight sugars like the maltotetraose I showed you above, as well as sugars known as ‘pentosans’1 – a fancy way of saying it’s a a member of a class of sugars made with only 5 carbon atoms in it instead of the 6 that are normally there.




Glucose: A normal 6-carbon sugar that is readily metabolized by yeast to make ethanol.





A pentose sugar. Good for making DNA (and haze…). Not so good for making ethanol or allowing yeast to reproduce.




Residual sugars are good. This means your beer has a small amount of sweetness to offset the hop bitterness. It also creates mouthfeel and that malty richness we generally like so much. But if there are too many non-fermentable sugars in there, you get a cloyingly sweet and (often) hazy beer.

That’s one of the reason big, bad, sticky IPAs use so many hops. They offset the sweetness of the non-fermentable sugars and you end up with a well-balanced beer that is even more loaded with beery goodness than your run of the mill lower alcohol beers.

OK – Let’s put this all together and use it to understand why New England IPAs tend to be hazy and why that is actually expected and not indicative of problems in the brewing process.

To do this, let’s look at the things that characterize the style as it is currently defined, since it is still evolving. There are 3 main characteristics that kinda define New England IPAs:

1) Relatively high gravity worts and therefore high(ish) alcohol contents. This is common among most IPAs. This means there are also a larger than normal amount of un-fermentable sugars in there.

2) Lots and lots of aroma hops. Whether added late in the boil or as dry hop additions, these beers are LOADED with aroma. On top of that, they tend to use a lot of “New World” hops that have even higher levels of aroma generating compounds in there that traditional varietals. Many of these aroma compounds are polyphenols.

3) The water used to brew these tends to be very “soft”, therefore having low mineral content. That gives some of that nice rounded mouthfeel that is cahracteristic of a good NE IPA, and it also accentuates the fruitiness of the beer.

So, basically, we hit the total trifecta of things that can be problems with beer, but are also acceptable in certain circumstances: High amounts of hop polyphenols, high amounts of residual sugar (whose sweetness is offset by high amount of hop bitterness), and lower than average levels of calcium.

Presto! You get both polyphenol derived haze and poor yeast flocculation. In both cases, however, the reason for those things means they will occur without producing significant off flavors in the beer. So, that big, juicy, hazy New England IPA will taste delicious, even if it looks cloudy as hell.


Now, one last thing…. Remember at the start of this treatise on haze when I said that New England IPAs were mostly legitimately hazy? Recall I kept putting that qualifier in there? OK, but why?

Well, that would be because sometimes brewers take shortcuts. Since the haze is such a hallmark of the style these days, if your New England IPA isn’t hazy enough, folks might just look down on it and say it won’t be hoppy enough or won’t have the appropriate residual sweetness, or juicyness, or … whatever. And, oddly enough, visual perception affects the way we perceive flavor. So, some brewers who are making clear, but otherwise wonderful and flavorful versions of the New England IPA will ‘cheat’ to make theirs hazy.3 (BTW, the ‘cheat’ term there is not my word. Others, however, have leveled that accusation in public spaces. It’s there to acknowledge that there is a division of opinion on what I am about to tell you.)

How? Get ready for this…. they add flour to their beer late in the boil process. The flour is non-fermentable and barely soluble, so it remains throughout the fermentation process. Hence, they get a thick permanent haze in their beer – despite the fact that it would be clear otherwise.

Photo courtesy David Sommbeer



very hazy IPA indeed. No inference made about how that haze came to be, though.





I’ll not editorialize on whether that’s a good thing or a bad thing. But, I will say, if you crack a New England IPA and it looks just a bit thicker in the haze department than the others you have been drinking, you might wonder…..


1) Turbidity and Haze Formation in Beer –Insights and Overview. Elisabeth Steiner, Thomas Becker and Martina Gastl J. Inst. Brew. 116(4), 360–368, 2010

2) Delcour, Jan A., et al. “The reactions between polyphenols and aldehydes and the influence of acetaldehyde on haze formation in beer.” Journal of the Institute of Brewing 88.4 (1982): 234-243.


Will Deutschman

Will Deutschman

I'm a college professor with expertise in biochemistry who gave up doing 'hardcore' biochemistry for brewing science research a few years back. Now I study yeast metabolism and sugar mobilization in malt. Working with students, we have been able to present our findings at professional conferences like the World Brewing Congress and American Society of Brewing Chemists annual meetings. Introducing students to the science behind beer is one of my favorite things to do in the world.

Outside of my "professional" life, I'm a BJCP certified judge, I bike and ski everywhere at every chance I get, and after a day of that, love chilling on the couch with my 2 dogs and 1 cat.

I also salve my need for intellectual challenge by designing and building fun brewing related projects, the best of which is my 100% solar powered brewing setup. #NerdAlert.
Will Deutschman

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