连续监测饮料生产中的硫化物异味

在饮料生产过程中，外部气味成分的添加和/或风味平衡的改变会产生"异味 "，这些气味会损害产品的口味，从而降低产品的质量。

就啤酒而言，异味可以在正常的发酵过程中产生，但也可能源于注入的二氧化碳中的杂质。

硫化氢是在发酵过程中产生的，具有代表性的“异味”。为了尽量减少其在生产过程中的产生，要控制发酵条件和酵母菌株的选择。

使用气相色谱法进行实验室气体分析的人工取样通常用于分析异味种类，如果需要对硫化物异味作出更快反应，则需要在线监测硫化物以进行质量控制。

Overview of Carbon Dioxide Production Process

Carbon dioxide (later, CO₂) for food and beverage industry is produced in two different ways. For carbonated soft drinks such as coke, it is produced as by-product of ammonia synthesis process in petrochemical plant. Then, CO₂ is purified in gas manufacturer’s purification plant, and finally sold to beverage manufacturers.

Figure 1: Production process of carbon dioxide as by-product from petrochemical plants

For brewery, carbon dioxide is produced as by-product during the yeast fermentation process. Breweries prevent CO₂ from going into the atmosphere by utilizing the gas for their products.

Figure 2: Production process of carbon dioxide as by-product from fermentation in breweries

The Reason to Measure Sulfide Off-Flavors in Carbon Dioxide

Sulfur, or hydrogen sulfide, is a gas that has a characteristic foul odor of rotten eggs, which can lead to bad smell and bad taste of beverages. CO₂ that is produced from fermentation process in brewery or from ammonia synthesis process in petrochemical plant have small amount of hydrogen sulfide.

For example, brewery (beer manufacturer) have fermentation process in their production line, where beer is manufactured from malt, hop, water and yeast. The yeast creates fermentation, where sugar (dextrose) breaks down into ethanol and CO₂ in the absence of oxygen.

C₆H₁₂O₆ (dextrose) → 2C₂H₅OH (ethanol) + 2CO₂ (carbon dioxide)

In the fermentation process, yeast consumes sugar and expels a large amount of CO₂ which can be “reclaimed” and used for beer. Unfortunately, during fermentation process, it also produces toxic, odorous sulfides which can foam up into the piping and contaminate the reclaimed CO₂. In order to continue using the reclaimed CO₂ byproduct but avoid the contamination of bottled beer with foul-smelling toxins, the reclaimed gas is run through deodorizing process shown in the Figure 3 below. However, sulfide breakthrough can occur if the CO₂ gas did not spend enough time in the scrubber. Employees are sometimes tasked with sniff-testing of the reclaimed CO₂, but this is an unhealthy practice and is very discrete to vigilantly prevent product contamination.

Another practice is batch measurement with gas chromatography conducted in the lab, but it will never give real time data, consequently it might be very hard to find out the contamination problem quickly. Finally, batch measurement is very expensive and contaminated CO₂, which exceeds purity standards is simply sold cheaply or dumped.

Continuous monitoring is a very cost-efficient solution, as it can immediately prevent the use of contaminated CO₂ in bottling beer as well as provide feedback to process control engineers for the processing time of sulfur removal. HORIBA can provide sulfide analyzer in CO₂ base gas as a continuous monitoring solution to prevent sulfide contamination in brewery products.