Beer and Pasteurisation - Sheep in Wolf's Clothing Brewery

What’s the first thing you think of when you hear the word “pasteurisation”? Unless you're vegan, it’s probably milk. So now you're thinking about a nice cuppa’ or a flat white that gets you going in the morning. Or maybe some porridge with bananas and honey if you’re one of those healthier people who eat a proper breakfast in the morning.

But those of us in the know, when we hear any talk of pasteurisation, we can only think of one thing. Beer. And why not? The human species’s love affair with beer goes back several millennia. Much of human history has been shaped around this prized and important source of sustenance.

In fact, the reason that lovely white stuff in your fridge doesn’t go sour in a matter of days is mostly due to beer (and wine). It’s also the reason a lot of other processed foods have much longer shelf lives than in the past. 

But these days, smaller and craft breweries like to shout “unfiltered”, “unfined”, and “unpasteurised” from the hilltops of social media and beyond. But what they don’t mention is “undrinkable”. And if you’re not pasteurising your beer, it’s more likely you will have unpredictable and undrinkable results over time. 

Let’s debunk the marketing terms and discuss just what pasteurisation is all about. 

Louis Pasteur and the History of Pasteurisation

We’ve mentioned ol’ Louis before and likely will bring him up again. Louis is the patriarch of pasteurisation as we know it. In many ways, he is the founder of modern beer by his discoveries relating to microbial fermentation and pasteurisation. Not to mention that his research helped lay the foundation for vaccinations. 

Funnily enough, when people are taught about pasteurisation, the topic is commonly related to milk. This is a bit of a misconception. The French chemist was a big lover of beer and wine. He was frustrated that his beloved libations would spoil and become sour over time. 

In 1864, while on a summer holiday in Arbois, Louis hit upon a revelation for the world. He found that heating up local wines for a short time allowed them to be aged without becoming acidic and tart. He then applied this same technique to beer with great success. 

What is Pasteurisation?

Pasteurisation is a process to treat packaged and non packaged food products with relatively mild heat. This is done to kill off microorganisms, preventing spoilage and lengthening the product’s shelf life. 

Typical pasteurisation temperatures range from around 55 ˚C to 75 ˚C. The time the products are held at those temperatures can be 10 seconds to 30 minutes. The temperature and time depend on the equipment being used and the microbial nature of the product. 

To measure the effectiveness of pasteurisation, brewers and other food producers use what is known as pasteurisation units (PU). Pasteur defined 1 PU as the equivalent of holding the food product at 60 ˚C for 1 minute

With pasteurisation, increasing time or temperature quickens the murder of microorganisms.   This means that the same effect can be achieved with a higher temperature or longer amounts of time. If you raise one, the other can be reduced to achieve the same result. Here is a fancy equation that demonstrates this relationship clearly. 

PU = t x 1.393(T-60) 
Where PU = number of pasteurisation units  
t = holding time in minutes  
 T = Holding temperature in °C  

Why Pasteurise?

Modern craft beer these days is commonly “can-conditioned” or refermented in the package. Like traditional real ale, a relatively small amount of yeast is still in suspension at the time of packaging. The yeast continues to chew on residual sugars, and voila! We end up with a nice sparkling and refreshing beverage.

For many more full-flavoured beer styles, this kind of packaging can help leave a maximum amount of haze and flavour (not necessarily the best for a balanced beer). At the end of the day, beauty is in the eye of the beholder.

Regional brewers around the world, including many big craft breweries in America, pasteurise all of their kegs and/or cans. There is much debate about what the actual flavour impact is for the drinker,, both anecdotally and scientifically. Any amount of heat quickens the ageing process of beer. This creates more of that delicious cardboard flavour from trans-2-nonenal that absolutely nobody enjoys. 

And of course many aromatic and other volatile compounds are destroyed in different amounts depending on how many PUs they get hit with. But is that only something brewers and supertasters can pick up? What isn’t up for debate is that pasteurising beer produces a much more stable product. 

Pasteurisation eliminates virtually all microorganisms within the beer from existence. Around 20 PUs leaves roughly 1 in 10 billion microorganisms alive. And at 30 PUs, we’re talking about eye-watering orders of magnitude. Those spoiling bastards don’t stand a chance! 

Brewing is all about good sanitation and hygiene. However, let’s not kid ourselves. It’s not general surgery and we’re not working in a sterile environment. Shit happens. Wild yeasts and anaerobic bacterias can make it into the package and begin creating their own tapestry of gustatory assault. 

Neutralising nearly all microbial activity in the tasty beverage means that there is a much lower chance of further metabolism of any remaining sugars in the beer. This is great for the consumer because it means you are spared from the following:

Unintentional sours- this is really a classic. You begin sipping that juice bomb but it starts to remind you of that orange juice you left out of the fridge for a couple of days. In fact, lesser breweries have tried to pull a fast one on the consumer by selling these products as purposely-soured beers. Take caution when a clean brewery puts out a random and unannounced “sour” beer.

Gushers- it’s always nice to get an unexpected talking point for your day. You get home after a hard day of work, crack open a cold one, and before you know it, your beer is on the ceiling. Most homebrewers are familiar with this lesson, but commercial beers taking off like a NASA booster rocket is becoming all too common.

Bottle bombs- at first it was all fun and games. But now it’s serious. Bottle bombs are no joke! Still fermenting packaged beer can become deadly shrapnel grenades for the unsuspecting drinker. It’s like playing a game of Russian roulette by yourself! Besides a public health hazard, these types of recalls can destroy a brewery’s reputation.

Methods of Pasteurisation

For commercial breweries, there are two main types of pasteurisation. 

Tunnel Pasteurisation

In tunnel pasteurisation, bottled and canned beers are passed through a long and narrow tunnel while hot water is sprayed over the top of each small pack. There will be several chambers to effectively step up the temperature of the beer before cooling it back down again. 

They are moved along on a conveyor belt at a speed to ensure each bottle or can reaches the desired temperature. Typically, tunnel pasteurisation will hold the beer at a peak temperature of 60 ˚C (140 ˚F) for 15-30 minutes. In this process, the package is filled, pasteurised, and then labelled. 

Flash Pasteurisation

Flash pasteurisation is also known as high temperature/ short-time (HTST) pasteurisation because that is what the technique is all about. That is higher temperatures that pasteurise in merely seconds. In commercial breweries, this method is normally achieved by a thermal bypass system where the beer flows one way, and hot or cold water flows the other way. 

Breweries use two or three-stage plate heat exchangers to facilitate this process. Very thin plates allow for instantaneous exchanges of heat between hot water and cold beer before rapidly cooling the product back down. With flash pasteurisation, the beer is typically held at 72 C (161.6 F) for  20-30 seconds. This will place the beer in the 15-25 PU range. This beer is now ready to be transferred to the package.

Tunnel vs Flash Pasteurisation

Tunnel Pasteurisation

Flash Pasteurisation

Stage in the process

After packaging 

Before packaging


Cans and Bottles

Kegs, cans, and bottles

How long at peak temperature?

15-30 minutes

15-30 seconds

Peak Temperature

60 C

72 C or higher


More expensive

Less expensive




Energy use

~40-50% regenerative

~95% regenerative

Contamination risks

None after pasteurisation

The package can be contaminated as well as the cooling portion of the heat exchanger

Negative effect on flavour*



*This is still up for debate in the brewing community

From a quick glance at this simple table, we can see the major pros and cons of each pasteurisation method. Overall, HTST pasteurisation is much more cost-effective, environmentally friendly, and versatile. However, tunnel pasteurisation offers greater peace of mind with superior product stability. 

Regardless of which method a brewery uses, it is up to their packaging and quality teams to determine the needed amount of PUs and to administer them with precision. This is something that each brewery must work out through its own research and experimentation. 

Low-alcohol and No-Alcohol–Why We Pasteurise

We may sound like a broken record, but with low- and no-alcohol brewing everything is more complicated. From creating recipes to packaging the beer, more control and caution must be taken every step of the way.

Earlier this month, we explained much about how to tailor your recipe and brewing process for low-alcohol beer production. If you aren’t familiar with those concepts, you can read more about low-alcohol brewing.

One of the many challenges of low/NA brewing is that these products are much more susceptible to contamination and spoilage than full strength beverages. A recent study by the Institute of Brewing and Distilling (IBD) found that spoilage in draught beer was 2-5 times higher in alcohol-free and low alcohol beers. They recommend that these beers need their own hygienically designed dispense systems, and we agree!

With full-strength beers, spoilage is less of a problem. This is because the yeast (S. cerevisiae) creates a rather hostile environment to non-brewing yeasts. Alcoholic fermentation produces ethanol and carbon dioxide which are toxic to most microorganisms. 

It also helps that hops provide antimicrobial compounds to the beer. These are especially useful at preventing anaerobic bacterias like lactobacillus from taking hold of “finished” beer. 

But herein lies the problem with lower alcohol beers. The lower the fermentation activity, the less spoilage-preventing alcohol and carbon dioxide in solution. And of course, with less malt, the beer is balanced with fewer hops. All added together, weaker and non-alcoholic beers are a recipe for disaster. 

We have learned this lesson on our own through the painful experience of a contaminated and soured Easy Rinder. Don’t worry, that beer has done the way of the dodo. We always take every precaution to prevent any spoilage from happening again. And that’s why we’ve made the decision to pasteurise that beer going forward.

What it means for you is that our beers will have the same great taste every time you try them (well, unless they’ve been sitting around unrefrigerated for months). You don’t have to worry about gushers and live fermented grenades in your hands. And trust us, if we make a sour beer, it’s always on purpose!

What we do know is that beers can taste better for much longer if we pasteurise them. Each member of our team can sleep easily at night knowing that we put out a stable and safe product on the shelf. 

It’s Up to Each Brewery to Decide

So there you have it. Hopefully, we’ve all learned something today. Pasteurisation isn’t for everyone, but it has great benefits. As beer drinkers and brewers, it’s best practice to keep an open mind about all things barley and hop-related. It’s always about quality and taste. So don’t knock ‘til you try it!

Every brewery will need to do what’s best for their beer. For Sheep In Wolf’s Clothing, pasteurisation will be involved in our 0.5% and below range. You can begin your journey with pasteurised craft beer by grabbing one of our starter packs. Cheers!


Nov 21, 2023

I just overheard pasteurisation in beer mentioned at my local. Decided to research a bit and came across your excellent and well written article. Kudos to the author. I have been both informed and entertained.

Feb 25, 2023
Ruwan Liyanagamage

We are a recruitment and consultancy company based in UK and Sri Lanka
One of our clients in Sri Lanka looking for a contract manufacturer in UK to serve UK and EU Markets. Are you willing to consider this offer and we will act as agents for this transaction

Expect your positive response soo

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