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On bitterness 

 Speaking of all categories of alcohol, beer is the only one that would focus on bitterness. Bitterness in beer is analogous to acidity in wine, which is responsible for the overall balance and the backbone of the beverage. Wines with poor acidity are bland and uninteresting, while beers without bitterness are boring. Lack of bitterness makes the beer tastes sweet and clumsy. In addition, bitterness relieves thickness or greasy feeling in oily food/ heavy sauce and cleans your palate. Therefore, we should learn to appreciate the bitterness of a beer: is it rounded or rough; is it clean or ambiguous; is it short or long? 

The source of bitterness 

The bitter taste in beer mainly come from the “alpha acids” in the hops. It has a low solubility except you boil it to dissolve in the wort. The bitterness increases with quantity of hops added and the boiling time. The quality of the bitterness is attributed to the choice of hops. In fact, alpha acids is a general term. It is the iso-cohumulone in the acid which brought a relatively rough texture. The proportion of alpha acid in various hops leads to different quality of the bitterness. Besides, hops are different from the aromas which will also affect your perception of bitterness! 

The measure of bitterness - IBU 

You may have heard of IBU (International Bitterness Units). It is a measure of alpha acid concentration in the beer. The higher the value, the bitter it is! The evaluation of IBU should be carried out in the laboratory, and most declared values of beers are estimated by the brewer when they design the recipe. IBU has a close relationship with the beer style. Craft beer generally falls between the value of 20-40, while some strong IPA may range 40-100! It is believed that the saturation point of IBU was around 120. However the craft beer industry likes to challenge by producing a beer with IBU 1000! Nevertheless, studies have found that it is indistinguishable by human when it goes beyond IBU 100. In that sense, the costly IBU 1000 beer is nothing more than just a gimmick. 

Other factors that affect bitterness 

In addition to hops, there are other elements in the beer which gives limited and indirect bitterness by altering your perception of bitter taste. For example, sweetness, derived from the residual sugar after fermentation, can mask the bitterness. Roasted malt gives coffee, chocolate and other bitter-like aromas, may further boasts the bitterness. In addition, water quality, alcohol level, body are also some of the factors contributing to the bitterness but not reflected in the IBU. As a consequence, IBU is only a reference value for drinkers while the style and how the brewers enhance the balance of bitterness are the key attributes you should consider. 

The Enemies of Bitterness 

Finally, you have to know that oxidization is the key enemy of bitterness. Amongst all the flavors in a beer, bitterness comes first to fade away following the aromas of hops (i.e. aromas of fresh fruit). A study claimed that over twenty percent of the bitterness dissipates within eight months after bottling. Be noticed that it presumes a storing environment in a room temperature in Western countries! Therefore in Hong Kong, particularly summer time, we should drink craft beer as fresh as possible. 



綜觀各種酒類,會注重苦味的,只有啤酒。苦,在啤酒裡,就跟酸度在葡萄酒裡的角色一樣,負責了整體的平衡及骨幹。酸度不足的葡萄酒,平淡無奇; 苦味不夠的啤酒,單一乏味。可以想像,如果啤酒少了苦味,整體會偏甜膩口,怎會令人回味?另外,在食物配搭方面,苦味可以緩和由濃厚醬重或油份食物所衍生的肥膩感,再度喚起你的味蕾。所以說,在品嘗啤酒時,苦味會是一個欣賞的維度: 是圓潤、還是粗糙;是潔淨清新、還是拖泥帶水; 是瞬間即逝、還是餘韻悠長... 



啤酒苦味的主要來自啤酒花的α 酸 (alpha acids), 它本身的可溶性很低,需要經過煮沸(boiling) 才可以溶進麥汁裡。在煮沸的過程中,啤酒花投放數量越多,煮沸時間越長,苦味也就越濃,持續得越久。至於苦味的質量,是圓潤還是粗糙的,有部份是歸因於使用酒花的品種。其實,α酸是一個統稱, 其中iso-cohumulone 所帶出的苦味就比較粗糙, 而不同品種的酒花,會有不同α 酸的組成比重, 所以產生的苦味也會有所分別。再說,不同品種的酒花所釋放的香氣也各有不同,這也會影響你對苦味的感覺呢! 

苦味的度量 – IBU 

你可能聽過IBU (International Bitterness Units)。它是量度α 酸在啤酒裡的濃度,即是說,數值越高, 苦味越濃!要實際量度啤酒的IBU 需要在實驗室進行,所以一般宣稱的數值大都是釀酒師在配方設計時的估算值。IBU 跟酒款有很大關係,不同風格會有不同的數值範圍,精釀啤酒一般在20-40 之間;不過,出名苦味強勁的IPA 類,它的範圍可以到40-100 !一般認為,IBU 的飽和點在120 左右。但是精釀界就是喜歡挑戰,真的有出產過IBU1000 的啤酒!但是,有研究指出,在IBU到達100之後, 大部份人的味蕾是分別不出來的... 所以1000 IBU 的啤酒,除了告訴你它是不惜工本外( 酒花成本是挺高的),可能只是噱頭了吧。


除了酒花外,啤酒裡還有其他東西,雖然不會直接供應苦味( 或供應得非常的少),但也會影響你對苦味的感覺。最明顯的是甜度,來自發酵後剩餘的殘糖;甜度越高,苦味感覺起來就比較輕。另外烘烤類麥芽,它本身已經帶微苦,加上它散發出來的咖啡、巧克力等香氣,就令你更加有苦味的感覺。其他的還有水質、酒精度、酒體等等。但是,以上因素都不反映在IBU 裡,所以對飲家來說,IBU 也只可以是一個參考值,重點還是你喜不喜歡苦味型的啤酒風格,以及釀酒師在增強苦味時怎樣去拿捏各種味道之間的平衡。


最後,你要知道,苦味的大敵是氧化。在眾多味道元素裡,繼酒花的香氣( 即如新鮮水果類的香氣) 之後,最快走丟的就是苦味。研究說,多於兩成的苦味會在裝瓶八個月內消散。但是,它說的是在西方國家的室溫!所以,在香港的夏天、如果在沒有冷存的情況下... 精釀啤酒還是新鮮喝的好!