瑞士干奶酪里为什么有很多小洞

 Gassy bacteria are behind all Swiss holed cheese. In order to make cheese, you need the help of bacteria. Starter cultures containing bacteria are added to milk, where they create lactic¹ acid, essential for producing cheese. Various types of bacteria can be used to make cheese, and some cheeses require several different bacteria to give them a particular flavor.

Propionibacter shermani is one of the three types of bacteria used to make Swiss cheese, and it's responsible for the cheese's distinctive² holes. Once P. shermani is added to the cheese mixture and warmed, bubbles of carbon dioxide form. These bubbles become holes in the final product. Cheesemakers can control the size of the holes by changing the acidity³, temperature, and curing time of the mixture. Incidentally, those holes are technically⁴ called "eyes," and the proper Swiss name for the cheese is Emmentaler (also spelled Emmental or Emmenthaler).

Swiss cheese has been in the news recently because the U.S. Department of Agriculture (USDA) created new guidelines that regulate the hole size of domestically produced Swiss cheese. The USDA reduced the standard size of the holes by half because new cheese-slicing machinery⁵ got caught on larger holes. The Swiss weren't pleased by the revised guidelines and insist that Emmentaler must have large holes. Considering how iconic those eyes are, we think they have a good point.

1 lactic   

adj.乳汁的

参考例句：

• Now they wear rubber fingers treated with lactic acid.现在他们带上了用乳酸处理过的橡皮指套。
• Lactic acid is an important organic acid of industrial importance.乳酸是一种具有重要工业价值的有机酸。

2 distinctive   

adj.特别的，有特色的，与众不同的

参考例句：

• She has a very distinctive way of walking.她走路的样子与别人很不相同。
• This bird has several distinctive features.这个鸟具有几种突出的特征。

3 acidity   

n.酸度，酸性

参考例句：

• This plant prefers alkaline soil,though it will readily tolerate some acidity.这种植物在酸性土壤中也能生存，但硷性土壤更加适宜。
• Gastric acidity would not prevent the organism from passing into the gut.胃的酸度不能防止细菌进入肠道。

4 technically   

adv.专门地，技术上地

参考例句：

• Technically it is the most advanced equipment ever.从技术上说，这是最先进的设备。
• The tomato is technically a fruit,although it is eaten as a vegetable.严格地说，西红柿是一种水果，尽管它是当作蔬菜吃的。

5 machinery   

n.(总称)机械，机器；机构

参考例句：

• Has the machinery been put up ready for the broadcast?广播器材安装完毕了吗？
• Machinery ought to be well maintained all the time.机器应该随时注意维护。