1
00:00:00,120 --> 00:00:02,035
Why does coffee
bubble when you pour?

2
00:00:02,035 --> 00:00:04,260
Watch the first splash of hot water.

3
00:00:04,260 --> 00:00:06,980
The grounds swell,
and little bubbles rise.

4
00:00:06,980 --> 00:00:08,480
That's the coffee bloom.

5
00:00:08,480 --> 00:00:11,480
To understand it, look
inside a roasted bean.

6
00:00:11,480 --> 00:00:13,830
Roasting creates carbon dioxide,

7
00:00:13,830 --> 00:00:16,855
and some stays trapped in
the bean's porous structure.

8
00:00:16,855 --> 00:00:18,580
Our cutaway shows that gas sitting

9
00:00:18,580 --> 00:00:21,180
in tiny spaces inside the coffee.

10
00:00:21,180 --> 00:00:23,780
Some gas gradually
escapes after roasting,

11
00:00:23,780 --> 00:00:26,105
before it ever meets brewing water.

12
00:00:26,105 --> 00:00:27,875
Grinding speeds up that release,

13
00:00:27,875 --> 00:00:30,325
but some gas can
remain in the grounds.

14
00:00:30,325 --> 00:00:32,200
Now return to our dripper.

15
00:00:32,200 --> 00:00:34,125
As the hot water wets the grounds,

16
00:00:34,125 --> 00:00:36,100
that trapped gas escapes.

17
00:00:36,100 --> 00:00:40,125
The bubbles make something hidden
inside the coffee visible at the surface.

18
00:00:40,125 --> 00:00:42,825
But a bigger bloom isn't
a better-coffee score.

19
00:00:42,825 --> 00:00:45,410
Roast, freshness, grind, and storage

20
00:00:45,410 --> 00:00:47,310
can all change what you see.

21
00:00:47,310 --> 00:00:50,660
A small bloom doesn't
automatically mean bad coffee.

22
00:00:50,660 --> 00:00:51,935
So those bubbles?

23
00:00:51,935 --> 00:00:53,710
A little gas from roasting,

24
00:00:53,710 --> 00:00:56,175
escaping as your coffee brews.