There are so, so many different types of cheese out there, but there’s one type you want when it comes to grilled cheese — the kind that’s nice and stretchy.

世界上有很多很多不同種類的起司，但是談到烤起司三明治，就非得用會牽絲的那種。

So then, how does chemistry get you that perfect, gooey grilled cheese?

那麼要怎麼用化學解釋那完美的牽絲、濃稠烤起司呢？

Time for a primer on cheese.

來談談起司的入門知識。

The first step of cheese making is to form curds out of milk.

製作起司的第一步就是讓牛奶形成凝乳。

Milk is 90% water, plus a mix of casein and whey proteins, lactose, calcium, and fats.

牛奶有 90％ 是水，加上一些酪蛋白和乳清蛋白質、乳糖、鈣質和脂肪。

Casein proteins float around in milk in tiny molecular clumps called micelles that refuse to stick together because they have same charge on the outside.

酪蛋白在牛奶中以膠束，一種微小的分子團形式漂浮著，因為外圍有相同電荷的關係而彼此排斥、不相碰。

These micelles hold around 2/3rds of the calcium in milk, and believe it or not, calcium is the key to the perfect grilled cheese.

膠束帶著牛奶中 2/3 的鈣質，而且信不信由你， 鈣質就是完美烤起司的關鍵。

To form curds, bacteria and enzymes are added to milk to make it coagulate, or go from a liquid to a solid or semisolid state.

要形成凝乳，需要在牛奶中加入細菌和酶使其凝固，或由液態轉為固態或半固態。

The bacteria converts lactose into lactic acid to drop the pH, which eliminates the charge of the casein micelles to help them stick together.

細菌將乳糖轉變為乳酸以降低 pH 值，減低酪蛋白膠束的電荷使他們易於結合。

Enzymes called rennet are used to speed up the process.

一種叫凝乳酶的酵素能加速這個過程。

Once the curds are formed, the whey and excess moisture is drained, and the little clumps can then be heated, bathed in salt water, and pressed together to meet the specifications of different types of cheeses.

凝乳形成後，便會瀝乾乳清以及多餘的水分，而那些碎凝乳塊就會經過加熱、泡鹽水以及壓合在一起而形成不同種類的起司。

Once pressed, the cheese is left to age from days to years depending on the style.

經過壓合後，起司會依據不同的種類熟成數日至數年。

The longer the cheese sits, the more lactose is converted into lactic acid, and the lower the pH; the lower the pH, the sharper the cheese.

熟成越久，越多乳糖轉成乳酸，pH 值也越降越低，pH 值越低，起司就越「濃烈」。

Remember that folks, because with grilled cheese, that pH level has a huge effect on the calcium found inside, and in turn, the texture when heated.

記好啊各位，pH 值對鈣質有很大的影響，並進而改變烤起司加熱後的質地。

If protein is the structural backbone of cheese, then calcium is the rebar that reinforces the backbone.

如果說蛋白質是起司的結構性骨幹，那麼鈣質就是增加骨幹強度的鋼筋。

It’s what grips all of the casein molecules together to form the micelles.

鈣質能將所有酪蛋白分子都抓在一起形成膠束。

Melty, stretchy cheeses have casein proteins that can break away and go with the flow and what that takes is a lower pH which lets the calcium ditch its job of holding all the casein together.

融化、牽絲的起司中的酪蛋白要擺脫束縛、自然流動，就需要低 pH 值的環境讓鈣質能夠將酪蛋白都聚集在一起。

That means more proteins break out of their cages to interact with the fats and moisture in the cheese, to make everything flow together as one big, lovely, gooey mess.

這讓更多蛋白質在掙脫時能夠與脂肪和水分相互作用，讓起司得以流動形成大量、美好、濃稠的混亂。

But if the pH is too low the cheese will release all of its oils when heated, leaving a curdly, clumpy disaster.

但是如果 pH 值過低，起司便會在加熱時釋放所有的脂肪，形成凝固、塊狀的悲劇。

The secret to getting the perfect cheese for a grilled cheese sandwich is to find one with the right pH to perfectly balance out the calcium and protein structure.

要製作烤起司三明治的完美起司的關鍵就是找到能夠平衡鈣質與蛋白質結構的酸度。

Cheeses with a pH range between 5.3 and 5.5 are right on the money, and here’s a handful of perfect examples.

pH 值在 5.3-5.5 之間的起司是最棒的狀態，有許多完美的實例都是如此。

OK, so here’s a Reactions Grilled Cheese Pro tip: If you’re in the cheese aisle confused about all the different types of cheddar, go with the mild one. It’s gonna have the texture you’re looking for, unlike its broken down, sharp older siblings.

來講些 Reactions 的專業烤起司技巧：如果你在買起司時不知道該選哪種切達起司，選味道溫和一點的吧！它會有你想要的口感，不像它其他分解、濃烈的陳年兄弟。

Oh, and what about those perfect yellow squares of processed American cheese?

那麼那些有美麗的黃色、加工過的方形美式起司呢？

This type of cheese is made by melting together two or more different cheeses like Colby and Cheddar, and adding an emulsifier such as sodium or potassium phosphate, which limits the amount of calcium holding everything together, all the while increasing the pH, sometimes up to 5.8.

這種起司是由兩種以上不同的起司融化後混合在一起，例如柯爾比乾酪和切達起司，並加入乳化劑，例如磷酸鈉或磷酸鉀，限制能夠將所有東西集結在一起的鈣質的數量同時提高 pH 值，有時候甚至高到 5.8。

This makes for a highly meltable cheese product with an exceptionally mild flavor.

這能做出容易融化且味道非常溫和的起司產品。

OK, folks, so now you get the picture so get the darn cheese already.

好的各位，你現在大概懂了，所以快去買些起司吧！

If any of you out there have any food-related questions, post them down in the comments for us but if you’re hungry for more food chem, check out this video on "The Chemistry of Pizza."

如果你們還有任何有關食物的問題，在下面的留言處向我們發問，而如果你還對更多食物的化學原理有興趣，來瞧瞧這部關於「披薩的化學原理」的影片吧！

Today’s episode was inspired by an absolutely amazing book called "The Kitchen as Laboratory", check out the first chapter by Jennifer Kimmel, "The Chemistry of a Grilled Cheese Sandwich".

今天這部影片是受到一本很棒的書的啟發，書名是「廚房如實驗室」，去看看 Jennifer Kimmel 所寫的第一章，「關於烤起司三明治的化學原理」。

A link’s down in the description, go get yourself a copy! Thumbs up, subscribe, and we’ll see you again soon.

下面說明欄中有連結，去買一本來看吧！ 按讚、訂閱，我們下次再見！