The aroma of Baijiu refers to an odor component that people inhale after smelling Baijiu with their sense of smell. It is a volatile aroma releasing substance molecule that diffuses in the air and enters the human nasal cavity to stimulate the olfactory organs. Through the transmission and organization of neural information, it produces a sense of fragrance, namely aroma. And these fragrant substances refer to some trace substances, which are usually divided into these five categories:

酸類：酸應算是我們挺容易感知的氣味了，當酒中酸類物質含量超過某個閥值時，你就會聞到那微酸氣味。酸有呈香、助香和緩沖平衡等作用, 尤其是揮發性酸類。

Acids: Acids should be a scent that we can easily perceive. When the acid content in wine exceeds a certain threshold, you will smell the slightly acidic odor. Acids have functions such as aroma formation, aroma aid, and buffering balance, especially volatile acids.

酯類：酯類是一類具有芳香性氣味的化合物, 多數呈現果香。它是白酒中重要的芳香物質, 主要起呈香作用, 可以在不同程度上增加酒的香氣, 并可決定香氣的品質。

Esters: Esters are a type of compound with an aromatic odor, most of which present a fruity aroma. It is an important aromatic substance in Baijiu, mainly playing the role of aroma, which can increase the aroma of liquor to varying degrees and determine the quality of aroma.

醇類：我們都知道，白酒的主體為“乙醇”。但這其它醇類，則多以呈味為主，不過也有呈香作用。比如我們描述藥香型酒常說濃郁的醇香, 愉悅的藥香, 兼有酯香。

Alcohols: As we all know, the main body of Baijiu is "ethanol". But these other alcohols are mostly flavored, but they also have a fragrant effect. For example, when describing medicinal flavored liquor, we often say that it has a rich and mellow aroma, a pleasant medicinal aroma, and a combination of ester aroma.

醛酮類：于說醛酮類，含這類物質多的要數醬香酒了，像醛類中的乙縮醛對保持酒香的均勻持久性就有一定的作用，我們常說醬香酒易儲藏，部分原因也在這兒。

Aldehydes and ketones: As for aldehydes and ketones, there are many such substances in sauce flavored liquor. Acetal in aldehydes plays a certain role in maintaining the uniformity and persistence of the liquor's aroma. We often say that sauce flavored liquor is easy to store, and some of the reasons are also here.

芳香族化合物：它在酒中的呈香作用是明顯的, 即使在酒 中存量很少, 但呈香作用很大, 如百萬分之一、甚千萬分之 一的情況下, 也能使人感受到香氣。除此之外，還有含硫化合物、吡嗪類和呋喃類也有一定的呈香作用。

Aromatic compounds: Their aroma forming effect in wine is obvious, even if they are rarely present in the wine, their aroma forming effect is significant, such as in the case of parts per million or even parts per million, which can make people feel the aroma. In addition, sulfur-containing compounds, pyrazines, and furans also have certain aromatic effects.

說到這，你可能要問了，這些呈香物質是怎么來的呢。它們一般有三個來源：

Speaking of this, you may have to ask, how did these fragrant substances come from. They generally come from three sources:

是原材料中帶入。像高粱就可分解為丁香酸，進而增加白酒的芳香。我們常說“好喝不過高粱酒”，那些名優酒中多以高粱為原料，正是這個道理。

Firstly, it is brought in from the raw materials. Sorghum, for example, can be decomposed into syringa acid, thus increasing the aroma of Baijiu. We often say that "sorghum wine is better than sorghum wine", and among those famous and high-quality wines, sorghum is often used as the raw material, which is precisely why.

其次是在發酵過程中的產物。比如多數醛酮類化合物就是微生物的代謝產物，而多種酯類物質則是通過生化作用的合成而產生香氣，像分子量小的酯類放香較大,可散發出各自特殊的芳香;而分子量大的酯類往往香氣較小, 但香氣幽雅。

The second is the products produced during the fermentation process. For example, most aldehydes and ketones are metabolites of microorganisms, while various esters are synthesized through biochemical reactions to produce aroma. Esters with small molecular weights, such as those with larger aroma, can emit their own unique fragrances; Esters with high molecular weight often have a smaller aroma but a more elegant aroma.

另外一種便是醇、酯、醛、酮等化合物在發酵、蒸餾或漫長的貯存過程中相互間引發的化學變化后生成的物質。如白酒在貯存過程中, 酒中的醇類可以被氧化為醛類，其中乙醛再與乙醇進行縮合作用可生成乙縮醛, 產生柔和的芳香。

Another type is the chemical changes caused by compounds such as alcohols, esters, aldehydes, ketones, etc. during fermentation, distillation, or long storage processes. For example, during the storage of Baijiu, the alcohols in the liquor can be oxidized to aldehydes, in which acetaldehyde can be condensed with ethanol to form acetal to produce soft fragrance.