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科学美国人60秒: 啤酒发酵跳跃式前进

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Beer Fermentation Hops Along

啤酒发酵跳跃式前进

The Allagash Brewing Company, in Maine, makes a lot of "bottle-conditioned" beers—brews that get their carbonation by fermenting a second time, in the bottle, as yeast belch out CO2. "And because they do bottle conditioning they're meticulous about monitoring package pressures. It's a way for them to follow the progression of this re-fermentation in the bottle." Thomas Shellhammer is a brewing scientist at Oregon State University. Who freely acknowledges: "It's a fun job. Science and beer."

缅因州的阿拉加什酿酒公司生产许多“瓶装”啤酒,它们通过在瓶中二次发酵获得碳酸,因为酵母会喷出二氧化碳。因为他们做的是瓶子调节,所以他们对包装压力的监测非常细致。对他们来说,这是一种跟踪瓶中再发酵过程的方法。Thomas Shellhammer是俄勒冈州立大学的酿酒科学家。他坦率地承认:“这是一份有趣的工作。科学和啤酒。”

At any rate, not long ago, Allagash noticed some very high pressures in some of their bottles. Not quite exploding. But alarming enough for them to give Shellhammer a call.

不管怎么说,不久以前,阿拉加什注意到他们的一些瓶子里有些压力很大。不爆炸。但这足以让他们提高警觉给Shellhammer打电话了。

What he and his colleague Kaylyn Kirkpatrick found was that hops—the bittering agent in beers—might be to blame. Because the aromatic flowers contain enzymes that can chew up starch. Typically, when hop flowers are added during the initial cooking of the fermentable brew, those key enzymes are denatured. And thus the flowers' only role is as a flavoring agent.

他和他的同事Kaylyn Kirkpatrick发现啤酒花——啤酒中的苦味剂——可能是罪魁祸首。因为芳香的花朵含有可以消化淀粉的酶。通常,当啤酒花在可发酵啤酒的最初烹饪过程中添加时,那些关键酶就会变性。因此,花的唯一作用就是调味剂。

But as the demand for hoppy beers has grown, brewers have been looking for other tricks to get those juicy, fruity, herbal aromas into beers. So they've been what’s called "dry-hopping" beers—dumping loads of hops into the beer during or after fermentation, rather than during the initial boil.

但随着啤酒花啤酒需求的增长,酿酒商们一直在寻找其他的方法来将这些多汁、果香、香草味融入啤酒中。这就是所谓的“干跳”啤酒——在发酵过程中或发酵后,而不是在最初的煮沸过程中,往啤酒里倾倒大量的啤酒花。

"There's an upward limit to how much hops you'd want to put in the kettle because the beers just get unpalatably bitter. But if a brewer focuses on dry hopping they can put very large amounts of hops into beer to create intense hoppy flavors."

“你想往水壶里放多少啤酒花是有上限的,因为啤酒会变得难以下咽。”但如果啤酒酿造者专注于干跳,他们可以在啤酒中加入大量啤酒花,以产生强烈的啤酒花味道。

Problem is, adding hops late doesn't deactivate their starch-attacking enzymes. And they're able to break down starches the yeasts weren't able to attack, unleashing even more sugar into the brew. And if yeast are still hanging out, as in Allagash's bottle-conditioned beers, that kickstarts additional fermentation. And that boosts alcohol by volume and carbon dioxide concentration—to potentially explosive levels.

问题是,晚加入啤酒花并不会破坏它们的淀粉攻击酶。它们能够分解淀粉酵母不能攻击,释放出更多的糖到酿造液中。如果酵母仍然存在,就像阿拉加什的瓶装啤酒一样,就会启动额外的发酵过程。这就使酒精的体积和二氧化碳浓度上升到潜在的爆炸性水平。

"Basically the hops are taking something that's considered by brewers to be unfermentable, and breaking them down to the point where they can actually re-ferment, or become fermentable, or potentially contribute to sweetness, as beer ages."

“啤酒花基本上就是把啤酒酿造者认为是不可发酵的东西,分解成可以重新发酵的部分,或者可以发酵的部分,或者可以增加甜度的部分,随着啤酒的老化。”

The full detective story is in the Journal of Agricultural and Food Chemistry. [Kaylyn R. Kirkpatrick and Thomas H. Shellhammer, Evidence of Dextrin Hydrolyzing Enzymes in Cascade Hops (Humulus lupulus)]

完整的侦探故事刊登在《农业与食品化学杂志》上。

And, in case you're wondering, Shellhammer's palate does align with his academic interests: "I'm kind of intrigued by the hazy, juicy IPA thing that's going on right now. I'm also a fan of sort of traditional old school IPAs." He’s the rare professor whose students use IPAs to raise their GPAs.

如果你想知道,Shellhammer的口味和他的学术兴趣是一致的:“我对现在正在进行的朦胧而有趣的IPA很感兴趣。我也是传统老式IPAs的粉丝。他是少有的教授,他的学生使用IPAs来提高他们的gpa。

Beer Fermentation Hops Along

The Allagash Brewing Company, in Maine, makes a lot of "bottle-conditioned" beers—brews that get their carbonation by fermenting a second time, in the bottle, as yeast belch out CO2. "And because they do bottle conditioning they're meticulous about monitoring package pressures. It's a way for them to follow the progression of this re-fermentation in the bottle." Thomas Shellhammer is a brewing scientist at Oregon State University. Who freely acknowledges: "It's a fun job. Science and beer."

At any rate, not long ago, Allagash noticed some very high pressures in some of their bottles. Not quite exploding. But alarming enough for them to give Shellhammer a call.

What he and his colleague Kaylyn Kirkpatrick found was that hops—the bittering agent in beers—might be to blame. Because the aromatic flowers contain enzymes that can chew up starch. Typically, when hop flowers are added during the initial cooking of the fermentable brew, those key enzymes are denatured. And thus the flowers' only role is as a flavoring agent.

But as the demand for hoppy beers has grown, brewers have been looking for other tricks to get those juicy, fruity, herbal aromas into beers. So they've been what’s called "dry-hopping" beers—dumping loads of hops into the beer during or after fermentation, rather than during the initial boil.

"There's an upward limit to how much hops you'd want to put in the kettle because the beers just get unpalatably bitter. But if a brewer focuses on dry hopping they can put very large amounts of hops into beer to create intense hoppy flavors."

Problem is, adding hops late doesn't deactivate their starch-attacking enzymes. And they're able to break down starches the yeasts weren't able to attack, unleashing even more sugar into the brew. And if yeast are still hanging out, as in Allagash's bottle-conditioned beers, that kickstarts additional fermentation. And that boosts alcohol by volume and carbon dioxide concentration—to potentially explosive levels.

"Basically the hops are taking something that's considered by brewers to be unfermentable, and breaking them down to the point where they can actually re-ferment, or become fermentable, or potentially contribute to sweetness, as beer ages."

The full detective story is in the Journal of Agricultural and Food Chemistry. [Kaylyn R. Kirkpatrick and Thomas H. Shellhammer, Evidence of Dextrin Hydrolyzing Enzymes in Cascade Hops (Humulus lupulus)]

And, in case you're wondering, Shellhammer's palate does align with his academic interests: "I'm kind of intrigued by the hazy, juicy IPA thing that's going on right now. I'm also a fan of sort of traditional old school IPAs." He’s the rare professor whose students use IPAs to raise their GPAs.


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