The Science of Cold Brew (McGill OSS)

2 minute read

A few weeks ago I finally had enough of the cold brew trend and decided to see what all the hype was about. I followed this recipe (because $5 at Starbucks is just too much for me), and was surprised to find cold brew wonderfully smooth, sweet and mild. I love coffee, and though I drink it with milk and sugar, I’ve never especially been bothered by the bitterness or acidity of traditionally brewed coffee. None the less, cold brew is quite amazing, and it left me wondering what the chemistry behind it was. 

It turns out that hot water (about 93 ℃ in most drip coffee makers ) accelerates the extraction of molecules and chemicals that, once mixed with water, form the coffee we know and love. Once brewed, the coffee continues to react with air and water molecules. This is why coffee goes stale. Heat accelerates these reactions (as it does most), so coffee left on a burner, or in your car, all day goes staler more rapidly. 

In cold brew, however, there is no heat to help extract these molecules and to cause the break down of others. The time the cold brew is left brewing allows the chemicals to be extracted from the coffee grounds much like the heat does, but you do get different amounts of different chemicals, leading to a different taste. Notably, many molecules that taste bitter are not extracted in large amounts in the absence of heat, which explains cold brew’s sweetness. You may have also seen cold brew being sold pre-packaged in stores, a possibility that is afforded to it due to the cold water not accelerating the ‘staling’ process.

So for once it seems like the hype was justified, though I’ll stick to making my cold brew at home. 

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Why do we get caffeine withdrawal headaches?

Originally published here:

Caffeine interacts with a neurotransmitter- adenosine- receptors, inhibiting the functions that adenosine would normally activate- namely, sleepy feelings. One theory behind caffeine withdrawal headaches is that with time your body adjusts to a new base level of caffeine, and creates more adenosine receptors to compensate. This would explain why you stop feelings alert after only 1 cup of coffee in the mornings after a while, and have to start having 2 or 3. It would also explain why your head hurts after skipping that coffee, as suddenly there are so many receptors available for binding that should be occupied by caffeine. While we’re not entirely sure why caffeine withdrawal headaches occur, we can say with certainty that after stopping caffeine intake the brain’s chemistry and electrical activity change. So perhaps your daily espresso is a bit more important than you realize.

The key to cleaning your teapot is chemistry

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Do you ever try to wash a mug only to be confronted by tea stains that just won’t budge? A little bit of chemistry may be just what you need to get your mugs back to white.

Brewed tea, green or black, contains many compounds, including many polyphenols. These are compounds found naturally in tea leaves that have antioxidant properties and contribute to the taste of tea. However, they are also responsible for the stains left in your mugs and teapots.

Polyphenols are a large group of complex molecules that are structurally similar in that they all contain simpler components known as phenols. Tannins are a class of polyphenols that provide tea with its characteristic hue, and are responsible for those annoying stains. Being largely impervious to scrubbing, how can these stains be removed?

A little bit of chemistry.

Black tea has a pH of 4.9, meaning that it is slightly acidic. While tannins encompass a wide variety of compounds, they all tend to be slightly acidic. As such, to remove them from the sides of your mug, you need to neutralize them with a base. the most readily available of which tends to be baking soda.

Just make a paste of baking soda and water, rub it onto your stained crockery, leave it for 20 minutes or so, and then wipe it off with a sponge. It certainly worked wonders on my now much-cleaner teapot.