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The Production Process – Fermentation

發酵過程

Fermentation is the process that transforms the sugary liquid, known as wort, into wash, which is similar to a strong beer with an alcohol content between seven and ten percent.   

Before the wort enters the fermentation vessel, or known as washback in Scotland, it has to be cooled down to approximately 20 degrees Celsius.  Then yeast is added to the wort in the washback, where it breaks down the sugars in the wort, converting them to alcohol and carbon dioxide.  This also generates whisky’s unique flavor compounds.

In fermentation, yeast multiplies as it consumes the sugars and amino acids in the wort.  Initially, fine bubbles are produced; in time, as the process accelerates, white bubbles will cover the entire surface of the washback.  This is the peak of fermentation and indicates that the yeast is producing ever more ethyl alcohol and carbon dioxide.  The temperature rises until reaching approximately 35 degrees Celsius, at which point the yeast stops multiplying.  Having completely consumed the amino acids and sugars in the wort, the yeast now begins to starve. To this point the process has taken roughly 24 hours.  Once it begins to starve, the yeast will perish over a period of 15-16 hours, during which time lactic acid bacteria will increase.  From here, the liquid requires an additional 10-20 hours to mature as the lactic acid bacteria feeds on the remaining sugars that the yeast could not consume, as well as on the amino and fatty acids emitted from the dead yeast.  This process generates both lactic acid and unique flavors.

In a little over 60 hours, the fermentation process is complete.  The resulting fermented liquid is called wash and has an alcohol content of approximately seven to ten percent.  In addition to controlling the starvation and destruction of the yeast, it is also important to properly gauge the maturation period of the wash.  If the maturation period is too short, the resulting liquor will be crude.  By allowing the wash time to mature, lactic acid fermentation will progress and produce a clean liquor.

The wash consists mostly of water, ethyl alcohol, esters and fatty acids.  Additionally, it contains several hundred recognized flavor compounds that are important in whisky.  The unique balance of these compounds produces unique flavors.  That balance is affected by various factors, such as the type of yeast and conditions of fermentation to best suit individual yeasts.

There are two types washback: wooden and stainless steel, where different vessels produce different character and flavors of wash, which ultimately has an influence on the style of the whisky.

Wooden washbacks, which traditionally are made of either Douglas Fir or Oregon Pine wood, tend to produce a liquor with richer flavors compared to stainless steel ones.  On the other hand, stainless steels are advantageous because they make it easy to regulate the fermentation temperature, and to keep the washback clean.  Regardless of material used, malt distillery washbacks have a capacity of approximately 30,000L, whereas the grain distillery ones could be up to 10 times larger!

 

 

發酵是將含糖液體(麥芽汁)轉化為酒醪的過程,類似於酒精含量7%至10%的濃烈啤酒。

在麥芽汁進入發酵容器 (蘇格蘭被稱為發酵桶) 之前,必須冷卻至約攝氏20度。然後將酵母加入麥芽汁中,將麥芽汁中的糖份轉化為酒精 (即乙醇) 和二氧化碳,同時衍生威士忌的獨特風味。

在發酵過程中,酵母消耗麥芽汁中的糖和氨基酸後自我繁殖,隨著酵母的活動加速,其產生出的微小氣泡不斷累積,直至白色的氣泡覆蓋整個表面。這是發酵過程的最高峰,此時酵母產生的乙醇多於二氧化碳,溫度上升至約35攝氏度,此後酵母將停止繁殖。在氨基酸和糖完全消耗盡後,酵母開始進入飢餓狀態,過程至此約需24小時。飢餓的酵母生命只能維持15-16小時,在此期間乳酸菌數目正在增加。麥芽汁需要額外的10-20小時熟成,期間乳酸菌會消耗液體中的剩餘糖份、以及從酵母殘體釋放出的氨基酸和脂肪酸,產生出乳酸和獨特的風味。

發酵過程約在60小時左右完成。所得的液體稱為酒醪,其酒精含量約為7-10%。 除了操控酵母的飢及破壞,測量酒醪的熟成期也很關鍵。熟成時間太短,得到的酒液將變得粗糙。給予足夠時間乳酸發酵才能產生出清澈的酒液。

酒醪主要由水、乙醇、酯化物和脂肪酸組成,還有幾百種味道化合物,在威士忌中產生重要作用。 這些化合物之間的相互作用和平衡產生出獨特的風味。這種平衡受到各種因素影響,例如酵母的類型、適合酵母的發酵環境等。

發酵桶分為木製和不銹鋼桶,不同的容器賦予酒醪不同的性質和口味,影響威士忌的最終風格。

木製發酵桶傳統上由道格拉斯冷杉或俄勒岡松木製成,與不銹鋼相比,它產生的酒液具有更豐富的香味;不銹鋼桶則比較容易調節發酵溫度及保持清潔。 不管使用什麼材料,一般麥芽蒸餾廠的發酵桶容量約為30,000L,而穀物酒廠使用的發酵桶,容量可能是其10倍!