What Does Turbidity Measure? Units and Scales in Beer
For decades, turbidity has been a bad word. Any sort of haze has been seen as a defect, a sign of contamination, and a curse on a batch of beer. Fortunately, craft brewers have brought the wonders of haze, or turbidity, back to the forefront, and some would even say they have compounded the issue.
Turbidity is now highly sought after across the globe in some beers, and many brewers are experimenting with their own hazy beers.
What It Turbidity?
Turbidity in beer is the visual impression a beer drinker gets long before taking that first sip. A filtered beer is perfectly clear, not cloudy at all, and has no haze. Beer with turbidity can be cloudy, murky, and almost completely opaque.
Why?
Beer is a complex mixture of hundreds of micronutrients, from proteins and nucleic acids to polysaccharides and lipids. It is the proteins, together with polyphenols, that form haze in beer. Carbohydrates in beer can also contribute to haze formation.
Turbidity has always been present in beer, and before the industrial revolution and the rise of commercial production of beer, haze was never seen as a bad thing or something to be avoided. It was naturally assumed that beer would be hazy.
Turbidity in Ancient Ales
Indeed, for centuries, ales served as a primary source of nutrition for families, from children to adults, and acted as both an important grain and protein as well as a beverage to maintain hydration. Ale was drunk at every meal, usually had a lower alcohol by volume percentage, and was thicker and hazier. Turbidity was welcome.
The Industrial Revolution Demands Clarity
Then, when corporations commandeered the beer industry, clarity became the name of the game.
Beer companies began filtering haze out of beer, and even introducing filter aids into beer to make the beverage not only crystal clear upon pouring but also perfectly clear on the shelf as well.
As with most things, supply created a demand, and soon beer drinkers frowned on any beer that had a hint of haze.
What Does Turbidity Measure?
Today, when we talk about turbidity, we are discussing the concentration of suspended particles in beer. We measure the incident light as it scatters at right angles in the brew.
You can now use laboratory equipment called a turbidity meter to measure “formazin turbidity units” or FTUs, to get an accurate measure of just how turbid your beer is. Typically, a turbidity meter should be small enough to carry around with you, measuring turbidity in your batches as you go.
Turbidity and Clarity Standards
Because we live in a day and age of reference points and standards, so that we may compare and contrast all things, of course we now have standards and scales for both turbidity and clarity.
When it comes to clarity in beer, we measure based on five levels.
- Brilliant <35 FTU
- Almost Brilliant 36 –69 FTU
- Slightly Hazy 69 – 138 FTU
- Hazy 138 – 276 FTU
- Very Hazy >276 FTU
Some clear beers can be much lower than 35 FTU, even down to under 10 FTU, as you will usually see with major beer corporations. However, it is a mistake to think that all golden or lighter beers are clear, as we have seen with hefeweizens and blonde ales, which can be quite turbid, rising up above the 70 FTU range.
And when it comes to haze, measuring over the 250 FTU range, we are usually discussing the issue of hops. But other factors can contribute to haze as well, including various ingredients included, the mashing regimen, yeast selection, and the cellar program.
Chill Haze
There is also chill haze to consider. This turbidity in beer occurs only when the beer is ice cold. Chill haze is caused by particles, namely the polyphenols and polypeptides that are considerably lighter weight, that are only visible when the beer is cold. As the beverage heats up, the hydrogen bonds are disrupted, and the beer seems to magically clarify.
This chill haze is only a problem for brewers concerned with issues of clarity. If clarity is sought after, you can choose from among various methods of clarification.
Methods of Clarification
Again, you do not have to clarify your beer. You can simply market your beer as on the hazier side and eschew a lot of extra filtration work or additives in your beer. Indeed, you could work the angle of having a pure, more organic beer on the market. There is certainly a niche for that.
If you insist on clarity, there are three primary approaches.
Fining
Fining beer for clarification involves adding materials like gelatin or isinglass with an electrostatic charge to combine with the yeast. Any solid particles will then settle out of the beer.
Filtration
Filtration involves passing the beer through a sheet made of cellulose or other types of screens to filter out yeast cells and proteinaceous material. Most filtration processes require at least two rounds, the first through a larger screen and the second through a much smaller, tighter screen, to ensure clarity.
Centrifugation
Centrifugation will usually not clear out all haze, but just enough to make the beer acceptable to the public and ready for consumption. This might be a good option for brewers interested in slowly stepping into the haze market.
In the end, high turbidity merely means a hazier, thicker mouthful of beer. It has nothing to do with contamination or defect.
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