Brewing Coffee (a Framework) updated 2/8/10

The Chemistry of Coffee Brewing...

When you brew coffee, hot water acts as a solvent, washing the soluble solids out of the coffee grinds and into the brew. If you dissolve table salt in water, you have a soluble solid. Brew methods that use paper filters have only the soluble solids in the cup. Some brew methods also allow insoluble solids to enter the brew. French Press, Espresso or Turkish Coffee are three methods that will have insoluble particulates suspended in the liquid. Insoluble solids will precipitate out of the brew over time, if you don't disturb the liquid. Hence your mug of French Press coffee might taste gritty nearing the end, and there is muddy residue in the bottom of the cup. Suspended solids add a sense of body to the cup, but can also add bittering tastes. Insoluble solids are bonded with the water molecules, and will not separate over time.

There are five main factors that control brewing results. First is the brew recipe, the ratio of water-to-coffee. More on that below. Second is the particle size of the coffee: finer grind means more surface area of the bean is exposed to the water. Third is the temperature of the water, ideally between 198-204 f, since water is a better solvent at near-boiling temperature. The fourth factor is contact time, how long the water and coffee are in contact with each other. And lastly is agitation, since stirring the coffee-water infusion increases extraction rate of soluble solids. Other factors influence the brew, but these are the main ones.

Most people find that when 20% of soluble solids are extracted from the coffee grounds, the brew has the best flavors. Too much extraction (too fine grind, too long brew time, too hot water, too much coffee in the recipe) and the brew is bitter. On the other hand, under-extraction results in a thin, weak cup. Simply using more coffee grinds cannot fix other brew problems: If you use 20 grams coffee and 350 ML of water and 4 minutes steep time to achieve 20% extraction (it should), using 40 grams coffee with a contact time of 1 minute to compensate will not result in a better cup.

Knowing these simple theories might help you troubleshoot that next bitter, weak, or a flat tasting cup. Here are a few general tips too:

1. Rinse all paper filters with hot water to wash away loose paper fibers that will give an off taste in the cup, especially when brewing small amounts.

2. Preheat your brew device, your French Press, Filtercone, etc. You can do both by simply heating extra hot water, and washing/preheating in one step.

3. Keep brewing equipment clean! Old sediments easily make for rancid flavors in the cup. A good rule of thumb is if you smell an odor from your coffee making equipment, clean it. If you cannot remember the last time you cleaned your brewer, clean it.

Here are some ideal coffee/water/time ratios for different brewing methods:

Amt of Coffee
Amt of water   by weight Infusion Time
Drip Brewing #1 drip filtercone 5 oz (150ml) 8 grams 2:30
#2 drip filtercone 10 oz (300ml) 16 gr 2:30
Clever Coffee Dripper 12 oz (360mL) 22 gr 4:00
#4 filter 20 oz (590 ml) 32 gr 2:30
Chemex 6 cup 30 oz (890 ml) 48.5 gr 2:30
Chemex 8 cup 40 oz (1180 ml) 64.5 gr 2:30
Chemex 13 cup 50 oz (1480 ml)  80.7 gr 2:30
*Tip: For drip cone methods, wet the grounds and let them "bloom" for 30 seconds, then pour slowly for 2 minutes
French Press :
 4T 16 oz (470 ml) 25.8 gr 4 to 6  min
8T 32 oz (950 ml) 51.7 gr 4 to 6  min
12T 48 oz (1420 ml) 77.5 gr 4 to 6  min
*Tip: Plunge after infusion time, then wait four minutes and pour slowly
Vacuum pot:
5 c Yama 20 oz (590 ml) 32 gr 45 seconds
Cona C 25 oz (740 ml) 40.3 gr 45 seconds
8c Yama/Cona D 32 oz (950 ml) 51.7 gr 45 seconds
*Tip: Infusion time measured once water is up in the coffee.There is a range of techniques - from adding hot water to the bottom bowl to letting the water rise to the top and then adding the coffee.  So you may want to check out a variety of techniques and find the one that works for you.
1/2 pot 8 cup 17 oz (503 mL) 26 gr 3 min
1/2 pot 10 cup 21 oz (621 mL) 38 gr 3 min
8 cup 34 oz (1000 ml) 57 gr 5 min
10 cup 42 oz (1240ml) 75 gr 5 min
*Tip: We close the drip stop switch on the brew basket, wait for the brew basket to fill, stir and then let it flow.

Water temperature for all brewing is 195 to 205 degrees. Typically this means water just off the boil.

On weighing ground coffee: It is much more accurate to measure roasted coffee by weight, since dark roasted coffee takes up more room than light roast. A "standard coffee scoop" (which in reality can vary widely) ought to be equal to two level Tblsp. Which would be 8 to 9 grams of dark roast, or 10 to 11 grams of light roast coffee.

The ideal brewing practice is: