什麼是二乙醯以及它如何影響啤酒?

Diethyl is a diketone molecule and one of the most popular and controversial seasonings in the world. Diacetyl has a distinct buttery flavor. It's what makes margarine taste like butter. This is why low-fat microwave popcorn tastes buttery. Even many dairies around the world use diacetyl judiciously. In the process of making fermented cream, the cream is inoculated with lactobacilli, which are released - right! Diethyl alcohol. The diacetyl produced during the culture process is a powerful flavor enhancer, making butter even more delicious.

Although diethyl is a natural product of fermentation, it is undesirable and even considered a defect in many types of beer. Ales and porters often contain small amounts of diacetyl, but beer usually does not contain any diacetyl.

Why is diacetyl so controversial?

Diethyl is a controversial flavoring agent because it is believed that inhaling high concentrations of diethyl over time can cause an irreversible lung disease called bronchiolitis obliterans. Colloquially known as popcorn worker's lung. There is no cure for this condition except for a lung transplant, and the success rate of this procedure is low.

Popcorn factory workers contracted the disease, and at least one person also contracted the disease after regularly eating microwave popcorn every day.

Therefore, while diethyl is generally considered safe when consumed in moderation, it appears to be unsafe when inhaled. As a result, many popcorn companies have removed diacetyl from their products. Some countries, such as the UK and EU countries, have banned the use of diacetyl as a flavoring in products such as e-cigarette liquids. For example, Platinum e-liquid from V2 Cigs UK does not contain diacetyl.

What effect does diacetyl have on beer?

People can taste very small amounts of diacetyl. For example, in California Chardonnay wines, the fermentation process often promotes the formation of diacetyl, which can be tasted in concentrations as low as 0.2 parts per million. In stronger-flavored wines such as Cabernet Sauvignon, the diacetyl concentration needs to be much higher (about 2.8 ppm) for people to taste it.

The reason some wineries encourage the formation of diethyl alcohol in Chardonnay is that it imparts the buttery flavor and mouthfeel that many believe is unique to the variety.

In beer, you can taste diethyl in concentrations as low as 0.1 ppm. Diacetyl gives the beer a creamy flavor; some may also interpret it as a butterscotch flavor. Additionally, diacetyl gives beer a slippery or greasy mouthfeel. Some people find that diacetyl makes beer appear fuller.

As mentioned above, some types of beer, such as ales and stouts, often contain small amounts of diacetyl. In beer, diethyl is generally undesirable - if the concentration of diacetyl is high enough, it is considered a flavor defect in any type of beer, as it is likely to be present due to bacterial contamination.

You will quickly learn that diacetyl can be present in beer due to improper sanitation during the brewing or bottling process. This is one reason why people sometimes react so strongly when they taste it in beer. Today, however, some small breweries are experimenting with diacetyl as a means of creating interesting new flavors. As a result, people began to think about diethyl alcohol with a more open mind.

Why is diacetyl present in beer?

Diacetyl is present in beer for two reasons. The first reason is because the yeast used in the brewing process introduces diacetyl during the fermentation process. Some yeast strains introduce more diethyl than others, but no matter which strain is used, diethyl will be present in the fermented beer. If you're a homebrewer, you can control the diacetyl introduced by fermentation in your product using techniques we'll explain later.

Another reason for the presence of diacetyl in beer - and in this case it is always considered a defect - is due to poor hygiene. Pediococcus and Lactobacillus cultures are lactic acid bacteria strains that can thrive in anaerobic and alcoholic environments, and low heat will not kill them. These bacteria produce diethyl as they multiply, and when this happens in beer, it creates a flavor that tastes like spoiled butter.

Since lactic acid bacteria can survive in alcohol without oxygen, they can continue to multiply in beer that has already been bottled. Bacterial contamination can cause pressure to build up inside the bottle, causing the beer to sour within just a few months of bottling.

How to Control Diacetyl in Homemade Beer

If you are a homebrewer, controlling the diacetyl content in your beer is a challenge you must deal with. Here are some tips to help you prevent diacetyl from ruining a batch of beer.

  • Sterilize your equipment and bottles carefully. As mentioned above, bacterial contamination can ruin beer after bottling. Proper sanitation is the only way to prevent this from happening.
  • Keep bottled beer cold. α-Acetyl lactic acid is a precursor to diethyl, which is converted to diethyl in bottled beer stored under warm conditions.
  • Introduce diethyl rest during fermentation. You can accomplish this by completing fermentation at a slightly higher temperature, then lowering the temperature again as the beer approaches its final gravity. Alternatively, you can simply wait. Instead of turning the beer upside down when it reaches its final gravity, leave the yeast in the mixture for a week. During the diethyl rest, the yeast consumes any diethyl present in the beer. When consuming diethyl, yeast produces acetoin and 2,3-butanediol—neither of which significantly affects the flavor of the final product.

Once you've removed the yeast from your beer, there's no longer any way to remove diacetyl from the product - so if you want to make sure your beer is diacetyl-free, the diacetyl residue left over from the brewing process critical stage.

During the diacetyl break, you can test the diacetyl content of your beer by simply taking a sample. Take two samples and place one in the refrigerator. Heat the second sample to approximately 140 degrees Fahrenheit and hold for 20 minutes. Place the second sample in the refrigerator. When the samples have cooled, drink them all. If you can taste butter in the heated sample, the yeast needs more time to consume the diacetyl in the beer.

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