The most magical stage of brewing.


Beer can be brewed in a few hours, and most are alcoholic within a few days, so why do we need to wait another week or month or even a few years before we can drink it? 

There are four stages to take a beer from raw ingredients to ready to drink and the first is the actual brewing, and whether it’s a pint of lager, a can of IPA, a cask ale or a bottle of saison, the basic brewing process of mixing grain and warm water to produce sweet wort then boiling that with hops is essentially the same, just with different specific ingredient combinations and volumes, and almost all beers can be made in half a day. It’s everything which happens after the brewing that makes the real difference. And that’s because of the yeast. 

When the yeast gets involved it changes a bitter-sweet non-alcohol liquid into a glass of beer, but that process involves limitless variables, with every beer needing different times, temperatures and even vessels – steel conditioning tanks, wooden barrels, bottles – to produce the best-tasting final version of itself. 

It begins with fermentation, as the yeast converts the wort’s sugars into alcohol and carbon dioxide, while at the same time releasing numerous other compounds which can contribute (positively or negatively) to aroma and flavour – things like diacetyl (buttery, oily), acetaldehyde (apple-like) and sulphur (eggy), plus esters (like banana or pear) and phenols (peppery, cloves). Most fermentations take place between 7ºC and 24ºC, and take three to eight days, and after it’s finished when we have the amount of alcohol that the brewers were aiming for, but the beer’s not even halfway to being ready to drink.

Following this – and often overlapping with the final days of fermentation – is a maturation period. This is where the main flavour development takes place and it’ll happen between 5ºC and 25ºC. One very important part of this involves the brewers manipulating the environment in the tank to encourage the yeast to reabsorb or convert some of the negative compounds in the beer, primarily diacetyl. 

Diacetyl is a buttery compound which is produced during all fermentations. The yeast will leave it behind while it’s busy consuming all the grain sugars, but near the end of the fermentation process, as the yeast is slowing down, the brewers can increase the tank temperature and the yeast will liven up again and reabsorb any diacetyl and convert it into a flavourless compound, a step in the brewing known as a ‘diacetyl rest’. Diacetyl is only appropriate in very small amounts in certain beer styles, and in most beers you don’t want any to be present. 

Also during the maturation stage, beer can be dry-hopped, and we expect some of the residual yeast in the tank to gradually be dropping through the beer to leave it looking clearer. 

Finally the beer is conditioned or lagered until it’s ready to be drunk and during this time all of the desired characteristics in the beer should be achieved. The yeast is still active here and it’s helping to produce carbonation, it’s still mopping up negative flavours and pushing forward the good ones, but it’s also working its way out of the beer by dropping to the bottom of the vessel. This conditioning can happen in tank, cask or bottle, and it could take a couple of days or a couple of years, and it will take place at varying temperatures, with most beers conditioning at 0ºC, although some beers will never get cooler than around 10ºC. As you can see, there’s no simple, single way to make beer and each style goes through many different variables.

“Great-tasting beer is a combination of a lot of things, like the quality of the hops, the wort boiling, the fermentation…” says Alex Troncoso of Lost and Grounded Brewers, but for their lagers, making them cold and slow is most important: “It simply makes a difference to the final beer: to the cleanness, the roundness, the palate structure – it’s just all the little things that take something from good to great.” 

Lagers typically ferment colder and slower than a regular ale, so it’ll be at 7-12ºC for 6-8 days instead an ale fermentation which will be 15ºC-25ºC for 2-5 days – the colder temperature naturally slows everything down, including diacetyl production and also its reabsorption. Then the beer will go through a maturation stage of around a week, including a diacetyl rest (at around 14ºC), and then it’s cooled to 0ºC for its extended conditioning or lagering period. Most great lagers will spend at least two weeks and up to six weeks cold conditioning (giving a total production time of four to eight weeks), during which time the beer is getting gradually cleaner, clearer, smoother and crisper. “When you don’t do the lagering properly, everything’s just a bit more spiky and not in its place,” says Troncoso.

Most great lagers will spend at least two weeks and up to six weeks cold conditioning

Jeremy Swainson, head brewer at Utopian Brewery, explains that “the technical reasons why you would lager is that in a classic lager fermentation you need a certain amount of time for diacetyl to be reduced. Then you also need a good amount of time for natural sedimentation to occur, so the yeast and polyphenol and protein bonds are settling out to the bottom,” meaning properties which can cause instability – physical and visual, like chill haze – in the beer are dropped from suspension, leaving a brighter beer. It’s also “for CO2 to be absorbed into the beer,” which gives you the final carbonation. 

Time mellows and sharpens the flavour of great lagers. So what if the beers were lagered for another month, will it continue to get better? The simple answer is: “Longer is not better,” says Swainson. The key phase of flavour development for most modern breweries comes in the fermentation and then the maturation time before it gets lagered or conditioned. But, he adds: “Any issues you get during fermentation aren’t necessarily going to be cleaned during lagering and if you put a beer that’s filled with diacetyl and acetaldehyde into lagering at 0ºC, it’s really not going to clean itself up.”

Where most lagers take over a month to make, most ales can be made in half that time thanks to the warmer temperatures which speeds all the processes up.

For Deya Brewing, the average time it takes to produce Steady Rolling Man, their hazy pale ale, is 14 days, at which point “that beer there is ready to drink straight away,” says Theo Freyne, the brewery’s founder.

It’s a four-day fermentation starting at around 19ºC and ultimately free-rising in temperature to 23ºC (fermentation in exothermic) where it’s held for two days for a diacetyl rest. Then the temperature is gradually lowered as the maturation continues, then the beer will be dry-hopped on day eight before it continues to cool over a few more days all the way down to 0ºC, where it’ll cold condition until it’s ready. Here the conditioning time allows the yeast cell count to drop (the beer might be hazy but shouldn’t be thick with yeast), the carbonation is increasing naturally (but can also be adjusted by the brewers), and the hop flavours are beginning to bloom.

Deya have increased their range of lagers and their Tappy Pils neatly demonstrates the difference between an ale and lager: Tappy starts fermenting at 8ºC then, after a week, it works its way up to around 14ºC for a diacetyl rest, which lasts twice as long as the ale diacetyl rest, then the temperature slowly drops to 0ºC where it will condition or lager for a full six weeks, where the beer will become almost bright and haze-free, and the flavours “will round out, and the beer’s going to benefit by becoming cleaner and more easy to drink,” says Freyne.

That refining of the flavour is crucial to a good lager, while an IPA wants to be more impactful, though the well-hopped beers still need to be properly conditioned, and compared to Deya’s pale ales, their IPAs and DIPAs take longer to ferment and then need more time to cold condition. “You can get a DIPA out in two weeks,” says Freyne, “but from our experience it’s going to be quite jagged, with a not very rounded profile, a bit aggressive, and green… We’re trying to make it so that they’re ready to go when people get them in their hands.” 

When a customer – whether a pub, bottle shop or you or I – buys a beer, we typically expect it to be ready to drink, but there’s one exception to that: cask ale.

Cask ale is the ultimate fresh beer, which is made to be brewed quickly and drunk quickly at its optimum freshness (before it fades fast with oxidation). The traditional temperatures and timings of a classic cask ale involve a warm fermentation of 15-20ºC for 3-4 days, then a few more days for some maturation in the brewery (sometimes in a maturation tank separate from the fermenter), where the yeast is clearing up any negative compounds (here apple-like acetaldehyde is often as prevalent as diacetyl), the flavour is rounding out, and the yeast is naturally settling (modern brewers may give the beer a bit longer in tank, especially if it’s dry-hopped), then unfiltered beer is filled into the cask and it’s sent to the pub where the cask will be left in the pub’s cool cellar (10-15ºC) for a week to undergo its conditioning period. 

Inside the cask are some additional sugars which the residual yeast consumes during a secondary fermentation, producing the gentle carbonation of a well-conditioned cask ale. Also in the cask are finings, which will draw the yeast to the bottom of the cask and leave a clear beer. The conditioning time for cask ales is what makes it a special drink, and when properly cared for by the pub, cask ales will reach a perfect yet short-lived freshness. 

While cask ale can be controlled relatively predictably, and is made fast to be drunk quickly, some beers are almost impossible to control or predict and can take months or years until they’re ready.

“There’s no textbook on how to do things, it’s sort of find your own path,” explains Mark Tranter, founder of Burning Sky Brewery who specialise in Belgian-style beers of mixed-fermentation. His flagship beer is Saison Provision and it’s fermented warm with a saison yeast strain (Belgian strains often ferment above 20ºC to encourage more fruity esters and spicy phenols to be given out by the yeast), which takes a few days. The beer then goes into large oak foudres which hold 2,500 litres of beer, where it’ll undergo its maturation at ambient temperatures for three to six months. What’s special here is that the foudre has its own unique microflora of different yeasts and bacteria (hence the ‘mixed-fermentation’) and they work differently from regular beer yeast and continue to ferment and evolve the beer over a longer period, with all sorts of unusual flavours working their way in and out of the beer until the brewers are happy with how it tastes. 

There’s a lot of magic... I quite like the romantic mystery

“It’s ready when we taste them and decide they’re ready,” says Tranter. “There is no way of gauging it other than the human palate.” So what’s going on inside the foudre? “I don’t know,” says Tranter. “There’s a lot of magic... I quite like the romantic mystery.”

When the beer has finished its maturation, it will be bottled and then conditioned in those bottles, where yeast and residual sugar will continue to ferment and produce carbon dioxide which is absorbed into the beer and gives it a lively effervescence.

Brewers need to make good wort, but it’s when they hand the beer over to the yeast and try to guide it through fermentation, maturation and conditioning that the beer can go from good to great – or go down the drain. You could drink a beer after four days but you’d be drinking something flat, cloudy and warm with a range of unpleasant flavours and aromas. 

Great beer – no matter the style – needs time to mature and then to condition into the perfect version of itself. And it’s always worth the wait to get great beer.

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