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:

酸类：酸应算是我们挺容易感知的气味了，当酒中酸类物质含量超过某个阀值时，你就会闻到那微酸气味。酸有呈香、助香和缓冲平衡等作用, 尤其是挥发性酸类。

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.

酯类：酯类是一类具有芳香性气味的化合物, 多数呈现果香。它是白酒中重要的芳香物质, 主要起呈香作用, 可以在不同程度上增加酒的香气, 并可决定香气的品质。

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.

醇类：我们都知道，白酒的主体为“乙醇”。但这其它醇类，则多以呈味为主，不过也有呈香作用。比如我们描述药香型酒常说浓郁的醇香, 愉悦的药香, 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.

醛酮类：于说醛酮类，含这类物质多的要数酱香酒了，像醛类中的乙缩醛对保持酒香的均匀持久性就有一定的作用，我们常说酱香酒易储藏，部分原因也在这儿。

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显的, 即使在酒 中存量很少, 但呈香作用很大, 如百万分之一、甚千万分之 一的情况下, 也能使人感受到香气。除此之外，还有含硫化合物、吡嗪类和呋喃类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.

说到这，你可能要问了，这些呈香物质是怎么来的呢。它们一般有三个来源：

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

是原材料中带入。像高粱就可分解为丁香酸，进而增加白酒的芳香。我们常说“好喝不过高粱酒”，那些名优酒中多以高粱为原料，正是这个道理。

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.

其次是在发酵过程中的产物。比如多数醛酮类化合物就是微生物的代谢产物，而多种酯类物质则是通过生化作用的合成而产生香气，像分子量小的酯类放香较大,可散发出各自特殊的芳香;而分子量大的酯类往往香气较小, 但香气幽雅。

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.

另外一种便是醇、酯、醛、酮等化合物在发酵、蒸馏或漫长的贮存过程中相互间引发的化学变化后生成的物质。如白酒在贮存过程中, 酒中的醇类可以被氧化为醛类，其中乙醛再与乙醇进行缩合作用可生成乙缩醛, 产生柔和的芳香。

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.