發酵處理如何影響咖啡風味?

 

2015年世界咖啡師大賽冠軍Sasa使用一種創新發酵處理,稱為水洗二氧化碳浸漬法,兩年後他有了自己的莊園而因此更投入在發酵處理的技術上。
事實上,在176月的布達佩斯世界大賽上,Sasa針對控制發酵處理帶來的風味、品質以及價格穩定性做了場演講,他也同意提供演講的部分資料給我們。
更多資訊請參考Come True Coffee官網
 
 
發酵處理後帶有內果皮的咖啡,來源:Ka’u Specialty Coffee
 


為什麼我們要討論發酵?

Sasa提到我們對發酵了解有限,但它卻非常重要。
他在會場提到:「我飛到世界各國品嘗咖啡,並且與超過五十個農民實驗咖啡處理流程,我也在我自己的農場實驗,發現在過往的傳統處理法上有太多不穩定的因素,而當中最不穩定的就是發酵帶來的影響」。
他提到事實上,有些例子顯示發酵如何提升或降低咖啡的品質甚至達到八分的差異。當大多數精品咖啡分數被定義在80-92分(滿分100)時,八分就會是一個驚人的差異。
 
 
Sasa實驗的冰處理咖啡,杯測分數為87.5分,來源:Sasa Sestic
 

什麼是發酵?

簡單來說,發酵是糖和澱粉分解成酸或酒精的過程,讓我們更深入探討,Sasa說酵母以及菌種對發酵是很重要的。
酵母發酵,稱為釀酒酵母,「這是一種天然野生的酵母,也被發現於葡萄、可可豆和其他水果中。目前應用在釀酒、可可豆處理以及咖啡處理上。」
而菌種則是乳酸菌。
在咖啡的天然發酵過程中,發生了不同的生物分解程序,酵母菌和細菌產生的酶開始分解果膠層中的醣。醣會分解脂質、蛋白質和酸,轉化成醇酸,這會改變咖啡豆的氣味、顏色、酸鹼值以及果膠層的成分。
Sasa還說世界上有很多不同的發酵方法,但主要分為乾式發酵以及濕式發酵兩種。
 
 
2017在匈牙利會場Sasa秀出的發酵成分圖
 

乾式發酵與其風味

「我們把果肉去除後就將帶有內果皮的咖啡放置在發酵槽中,發酵助長了咖啡的甜味、巧克力以及水果風味」,但發酵有一個挑戰就是溫度的控制。既然溫度可以影響發酵程度,同樣的也會負面的影響過程的穩定性及其風味。
 
溫度在乾式發酵帶來的影響,來源:Sasa Sestic
 
上圖虛線左邊的示意圖,代表我們將咖啡以均溫16度發酵24小時,咖啡嚐起來很棒而且風味感受平衡度佳。
而上圖的右側,則代表以26度的溫度發酵24小時,可以看到標記的粉紅色區塊,這會在發酵太長時發生,醇性酸會主導發酵,會導致過多的醋酸、乾燥感以及金屬般的味道。
 
 

濕式發酵及其風味

你可能聽過有人描述濕式發酵為雙重水洗、雙重發酵、肯亞式水洗等等,這在東非國家很常見,著名於乾淨清澈的風味特性,但Sasa形容這種處理方式增添了杯中風味。
「當我們去除果肉後,將帶內果皮的咖啡放入水中,水會幫助延長發酵時間,形成咖啡更柔和的醇厚度、豐富酸質以及更優雅的風味特性。」
 
在衣索比亞產地檢查計畫建置的發酵槽,來源:Project Origin
 
當然這不代表這種處理沒有挑戰性,Sasa提到溫度以及水質一樣會影響結果。
Sasa:「幾年前,我跟薩爾瓦多的Santa Rosa的莊園主Raul Riviera一起做實驗,我們使用雨水而不是用泉水發酵,雨水會從咖啡果實中吸收許多水果風味成分及糖分,結果導致杯測分數降低了五分,這咖啡嘗起來平淡且沒有鮮明的風味。用來發酵的水其影響還有很多要研究的地方。」
 
 
上圖左側為浸泡30小時泉水的咖啡果實,ph值為7.5 / TDS 180
上圖右側為浸泡30小時雨水的咖啡果實,ph值為6.5 / TDS 30
來源:Sasa Sestic
 

更多數據造就更好的咖啡

Sasa在咖啡處理法的實驗上為其中一個領頭者,從他新穎的冰處理法(這個直到他出書之前都會是商業機密)直到著名的水洗二氧化碳浸漬處理。
由於咖啡業中相關研究非常少,Sasa以葡萄酒及啤酒釀造技術著手研究。Sasa:「Clonakilla酒廠的老闆Tim Kirk幫我很多忙並帶給我不少激勵,他的酒廠在我的家鄉坎培拉」。
「當我第一次拜訪Tim時,我對他的設備配置印象深刻,他非常清楚雨水會落在葡萄園的哪個地方,他也很清楚風的溫度以及會如何影響葡萄酒的風味。這實在很吸引人。我從沒見過有人如此了解氣候,還有氣候如何影響產品」。
 
 
Clonakilla酒廠的Tim Krk解釋發酵葡萄酒時的變因,來源:Sasa Sestic
 
但形容Tim對天氣瞭若指掌並不貼切,因為他甚至能控制天氣。
Tim可以控制發酵時環境的溫度及濕度,他說只要控制不同的溫度和時間,他就可以讓葡萄酒達到不同的風味層次」。
「他使用雙層絕緣不鏽鋼容器,增加發酵的清澈程度。他會監控並記錄酸鹼值、酒精與二氧化碳濃度,以確保有達到他期望的釀造結果」。
這種依數據驅動的操作方式,讓Sasa改變了他處理咖啡的方式。
 
Clonakilla酒廠的不鏽鋼發酵槽,來源:Sasa Sestic
 

發酵實驗

「想像一杯風味很棒、特性鮮明的水洗與日曬咖啡。我想要創造一種處理技術,可以發揮咖啡香氣、風味並在酸質、甜味上有良好的平衡。然後更重要的是,我想要創造讓這個技術在農場端是可被複製的,就像Tim處理他的葡萄酒一樣。」
以下是Sasa的處理流程:

 

Step 1

首先在不鏽鋼桶中去除果皮及果肉,「使用不鏽鋼是因為我們可以處理出更乾淨風味的咖啡,此外我們可以依照空間溫度的不同將容器移動位置;我們也可以密封這些桶子。」
 

Step 2

接下來將桶子移到室內,在室內溫度更容易掌控,但Sasa還在收集這部分會如何影響咖啡處理的數據。然而,他已經觀察出一些有價值的結論:「如果想要得到豐富的酸質,應該要用較低溫(4-8°C)發酵。若要得到更多甜味,就要用較高溫發酵(18-20°C)」。
 
發酵程序前在不鏽鋼桶中的咖啡果實,來源:Ka’u Specialty Coffee
 

Step 3

接下來將桶子密封。「就我的經驗,這個階段會發展較多香氣,增添花香到咖啡中」。
 

Step 4

最後,也是最重要的步驟,將二氧化碳注入。「之所以會選擇注入二氧化碳,是因為只要沒有了氧氣,將會降低果膠層糖分的分解程度,酸鹼值改變的幅度也會大幅降低,這代表我們可以減少酒精類酸質的產生」。
「二氧化碳可以在22度下延長發酵時間至三天,甚至可以在較長時間低溫狀態下,不會發展出乾澀感和醋酸的刺激酸味-這常會在三天的乾式發酵中發生」。
Sasa想要像Tim一樣掌握每個環節的數據,「我們也會測量並記錄發酵過程的酸鹼值、二氧化碳濃度以及溫度,然後每次都可以複製這些發酵條件。」
 
二氧化碳浸漬法:注入二氧化碳,排出氧氣。來源:Sasa Sestic
 

持續改善方法

Sasa並不滿足於他的冠軍頭銜:他督促自己找到更多方法,改善透過發酵帶來的咖啡風味。「去年,我喝到巴拿馬Morgon莊園Jamison的咖啡,太好喝了。但我想要更多甜感、更深層的風味、更多花香調性,所以在幾杯黃湯下肚後,我們決定來進行二氧化碳浸漬處理法。」
但這個跟以往操作過的二氧化碳浸漬法不一樣,「我們決定用較高的溫度20°C發酵以促進咖啡甜感,並延長二氧化碳浸漬發酵的時間到65小時,促進風味的豐富度更多的發展。」結果我們得到更多甜感,更佳的質地、更清晰的風味特性。「最終咖啡的杯測分數提升了2.5分。」Sasa說道。
 
 
發酵監控曲線,來自Sasa Sestic2017在匈牙利會場的演講資料
 
 
透過這種處理法,他帶來讓人期待的風味,並且他們提供更多機會讓消費者、咖啡師、咖啡比賽選手拿到好咖啡,還有生產者可以穩定的得到好的賣價。
「以我的觀點來看,我相信沒有所謂完美的咖啡品種,也沒有完美的處理法。然而,如果我們可以了解不同咖啡品種其潛在的風味特性,以及其優缺點,並且透過二氧化碳浸漬法或其他可控制的發酵方法來處理,我們可以強化這些咖啡的優點並修飾掉缺點。當我們在發酵這個環節得到好的處理數據時,我們就可以複製出這個美好的風味了」。
 
Original source:

 

 
 
 
In 2015, Sasa Sestic won the World Barista Championship with a coffee that had been washed carbonic macerated, an innovative fermentation method. Two years later, he has his own farms and is consequently even more interested in fermentation.
In fact, last month, he spoke at Re;co in Budapest on the impact of controlling fermentation on flavour development, coffee quality, and price sustainability. He agreed to provide us with some information about his presentation.
coffee beansDried coffee in parchment after fermentation. Credit: Ka’u Specialty Coffee

WHY DO WE NEED TO TALK ABOUT FERMENTATION?

One thing that Sasa is firm about is that we know so little about fermentation – but it’s so important.
At Re;co, he said, “While travelling all over the world, tasting coffees and experimenting with processing with over 50 producers, and also on my farms, I realised that there are a lot of inconsistencies in traditional processing techniques. And most of these inconsistencies are coming from fermentation.”
In fact, he explains, “[Fermentation] is where we have increased, and also decreased, the quality of coffee, in some instances, by eight points.” When most specialty coffees cup somewhere between 80 and 92 points out of 100, eight points is a phenomenal difference.
coffee fermentationSasa’s experimental ice processed coffee which cupped at 87.5 points. Credit: Sasa Sestic

WHAT IS FERMENTATION?

Simply put, fermentation is when sugars and starches are broken down and become acids or alcohol.
Let’s look at this in a little more detail. Sasa tells me that yeast and bacteria are important for fermentation to occur.
The yeast, he tells me, is called Sacromises cerevisiae. “This is a microorganism and it is a natural, wild yeast that is also found in grapes, cacao beans, and other fruits. It’s present in winemaking, cacao bean processing, and also coffee processing.”
As for the bacteria, it’s called Lacto bacillus.
“During natural fermentation in coffee, there are different biological processes that occur in which enzymes produced by the yeast and bacteria start breaking down the sugars in the mucilage,” Sasa explains.
“So, the sugar degrades its lipids, proteins, and acids, and converts them into alcohol acidic acids. This changes its smell, colour, pH, and the composition of the mucilage.”
He also tells me that there are different types of fermentation around the world, but two in particular deserve attention: dry and wet fermentation.
fermentation
The ingredients for fermentation, a slide from Sasa Sestic’s 2017 Re;co presentation.

DRY FERMENTATION & FLAVOUR PROFILES

“This is where we pulp and place the parchment in concrete tiled pools,” Sasa says. “This fermentation will help encourage sweet, chocolate and fruity characters out of coffee.”
But it comes with a challenge: controlling temperatures. Since temperature affects the rate of fermentation, Sasa explains that it can negatively affect consistency and flavour.
fermentationEffects of temperature in dry processing. Credit: Sasa Sestic
“In the picture [above] on the left,” he continues, “we have fermented this coffee for 24 hours at an average temperature of 16°C. This coffee tasted great – nice and balanced.
“In the picture on the right, we also fermented for 24 hours but at 26°C, so 10 degrees more.” He then points out the pink in the bean. “This happens when we spend way too much time fermenting the coffee, and alcohol acidity starts dominating fermentation. It results in notes of  vinegar, and dry and metal characters.”

WET FERMENTATION & FLAVOUR PROFILES

You’ll hear wet fermentation described as double washed, double fermented, Kenyan washed, and more. It’s common to East Africa where it’s known for its cleanliness. But Sasa explains that it adds far more to the cup.
“After we pulp the cherries, we cover the parchment in water. Water will help to extend fermentation time and will result in a softer body, complex acidity, and more refined flavour profile,” he explains.
fermentationHabib of Project Origin inspects unfinished fermentation tanks being built in Ethiopia. Credit: Project Origin
This doesn’t mean there aren’t challenges, of course. Sasa cites inconsistent temperatures and water quality as the main ones.
“A few years ago, I experimented with Raul Riviera from El Salvador, owner of Santa Rosa farm,” he says. “We used rainwater as opposed to spring water for fermentation… The rainwater absorbed a lot more fruit and sugars from the coffee cherries. We decreased our score by 5 points… The coffee simply tasted flat and had no character.”
There is much more to learn about how different types of water affect fermentation, he adds.
fermentationCoffee cherries after 30 hours of immersion in spring water (left), which had a 7.5 pH and TDS of 180, and rainwater (right), which had a pH of 6.5 and TDS of 30. Credit: Sasa Sestic

MORE DATA, BETTER COFFEE

Sasa has been one of several industry leaders experimenting with processing methods, from his new ice processing (the details of which are a closely kept secret until his book on it is published) to his famous carbonic maceration.
With little research to build on in the coffee industry, he looked to wine and beer instead. “One man, in particular, helped me and inspired me,” he says. “His name is Tim Kirk and he’s the owner of Clonakilla Winery, which is a beautiful winery located near Canberra, my home.
“When I visited Tim for the first time, I was so impressed with his set-up. He knows the exact rainfall on his vineyards, as well as the wind temperatures and exactly how this impacts the flavour profile of his wine. I found this fascinating. I had never seen anyone with such a thorough understanding of climate and how it affects their product.”
fermentationTim Kirk of Clonakilla Winery explains variables for fermentation in wine. Credit: Sasa Sestic
But Tim didn’t just understand the impact of climate – he controlled it.
“Tim controls the temperature and humidity of the environment for fermentation. He explained to me that with different temperatures and also times he can achieve different flavour complexities in his wine.
“He uses double-insulated stainless containers to increase the clarity of fermentation. The pH, alcohol and carbon dioxide are monitored and recorded to ensure he achieves the consistency he desires.”
It’s this data-driven approach that drove Sasa to change how he processed coffee.
fermentationThe stainless containers used in Clonakilla Winery. Credit: Sasa Sestic

EXPERIMENTING WITH FERMENTATION

“Imagine the best attributes of washed and natural process coffees in one cup, with amplified terror and varietal characteristics,” Sasa says.
“I wanted to create a technique where we can enhance aroma, flavour… tailor the taste balance of acidity and sweetness. And also, even more importantly, I wanted to create a process that we can replicate at farm level every single time, just like Tim does with his wines.”
Here is his process:

Step 1

He begins by pulping the cherries in a stainless steel container. “The reason we use stainless is because we can create a cleaner taste profile,” he adds. “Also, an added benefit is that we can move the containers between different rooms with different temperatures; also, we can completely seal these containers.”

Step 2

The next step is to move the containers indoors, where the temperature is easier to control. He is still collecting more data to further understand the impact of this.
However, he has already gained some valuable insights: “If we wish to have a complex acidity, we should ferment at a lower temperature, 4–8°C. For more sweetness, use a higher temperature, 18–20°C.”
coffee cherriesCoffee cherries in stainless steel tank before fermentation begins. Credit: Ka’u Specialty Coffee

Step 3

Next, the container should be sealed. “In my experience, this develops more aromatics and adds more floral notes to the coffee,” Sasa explains.

Step 4

Finally, he injects carbon dioxide: a crucial step. “The reason why I have decided to flush carbon dioxide is because, without oxygen, we slow down the breaking down of sugars from the mucilage dramatically. The pH also drops at a lot slower pace, which means we encourage  less alcohol acidity.
“Carbon dioxide helps me to extend fermentation by up to 3 days at 22°C, and even longer at lower temperatures, without getting dryness and a vinegar taste – which is normally the case with three days of dry fermentation.”
Just like Tim, Sasa is determined to measure everything. “We also measure and record the pH, carbon dioxide, temperature of fermentation… and we can replicate the profile every time.”
fermentationCarbonic maceration: carbon dioxide enters the tank, oxygen exits. Credit: Sasa Sestic

CONTINUOUS IMPROVEMENTS

Sasa is not content to rest on his laurels: he is driven to find even more ways to improve coffee flavours through fermentation.
“Last year, I tasted coffee from Jamison Savage in Panama Morgan estate and the coffee was beautiful. But I wanted more sweetness, and more depth, and even more floral characters. So after few bottles of wine, we decided to do carbonic maceration process.”
But this wasn’t going to be the same carbonic maceration process as before. “We decided to do carbonic maceration process at a higher temperature, 20°C, to encourage sweetness. And we extended [the duration of] carbonic maceration fermentation all the way up to 65 hours to encourage more flavour complexities.”
The result? More sweetness, more texture, and a more distinct flavour profile. “We improved the coffee by 2.5 points,” Sasa says.
fermentation“Fermentation Monitoring Curve”, a slide from Sasa Sestic’s 2017 Re;co presentation.
He is left excited by the flavours of the carbonic macerated coffees, and the opportunities they offer – to consumers, to baristas and competitors, and to producers who, he believes, can receive consistently good prices this way.
“Personally, I believe that there is no perfect coffee varietal, and there is no perfect process,” Sasa says. “However, if we can better understand the potential for flavour complexities in different varietals,  their strengths and weaknesses, and with carbonic maceration process or other controlled fermentations, we can try to highlight these strengths and improve weaknesses.  And once we have the perfect recipe [for fermentation], we can replicate this flavour profile.”