Welcome to The Science of Coffee.
I’m Renee and today we are going to be talking about the difference between hot brewed coffee and cold brewed coffee.
Why do they taste different and why it’s happening.
Because remember, coffee is chemistry.  
Let’s dig in.
Coffee’s actually made up of a lot of different compounds.
Including sugars and oils and aromatic compounds.
And these compounds naturally oxidize or break down, but adding heat is going to speed up that process.
So the first thing you notice when you brew hot coffee, is all this kind of steam that’s coming out. 
And if you lean in, you get a really good idea of that aroma of the coffee.
This is because that heat is increasing the rate that those aromatic compounds are breaking down.
And this is going to give hot coffee a really good balance between the acid and the sugars that are both found in there.
Cold brew is using twice the amount of coffee and brewing it in the fridge or cold temperatures. 
So this will actually slow down that process of oxidation or breaking down those compounds.
And it will give it a different flavor.
So let’s compare.
So this is the hot brewed coffee.
Nice balance of acidity and sweetness, really good rounded feel and kind of dry on the finish.
Now let's go to the cold brew version.
I noticed immediately that the aroma is different — smells so much sweeter. 
And the flavor is different as well. I get a little bit less acidity and a lot of sweetness and kind of a smooth texture in this compared to the hot.
Let’s talk about why that’s happening.
The rate of oxidation in cold brew coffee is much slower.
All the different compounds will oxidize at different rates but sugars take longer.
And so when you pick up your cup of cold brew coffee you’ll have a lot more residual sugar in ratio to the acid.  
The result is a cold brewed cup of coffee with sugar as the forefront of the flavor.
Whereas the hot cup of coffee is going to have both the balance of that sugar and acidity.
So the process is the same. Oxidation.
The rate is just different, and that’s chemistry.
