cold-brewing notes

useful sizes, proportions, temperatures, etc

Overview

These notes are meant to aid cold-brewing efforts.

Early attempts have varied from 'wonderful' to 'mediocre' so this page was made to help track different coffee-making sessions to learn the subtleties of what works, what doesn't.

Cold-brewed coffee isn't well known. It doesn't take long to make and is said to reduce the oils and acid which are in normally brewed coffee. Some people will like it; some people won't. BTW, cold-brewed coffee doesn't have to be served cold. Microwaving it before serving does not reintroduce the now-missing acids, oils, ketones, and amids.

Cold-brewed coffees will occasionally show up at the tastings.

General Technique

  1. put grounds in a container. I use glass containers with a mason jar type lid. I purchased several at Pier 1 Imports for $6 ea. I believe each holds about 1.5 quarts (about 1500 mL).
  2. add appropriate amount of water over grounds. I use 5.9 cups water + 1.2 cups ground coffee. Stir.
  3. I let it brew for 20 to 24 hours. If I think about it, I'll open the jug and stir it every few hours. I haven't seen that this makes a difference.
  4. filter out the grounds. This step needs work as it's slow and labor intensive. Slowly pouring the container's contents onto paper towels in a colinder work more quickly than using #4 filters. But the paper towels don't remove the finest sediment.
  5. microwave the coffee to serving temperature, minimum 135.
  6. serve
Most readers won't need any of the information below - except maybe the links at the very bottom of the page.

A little science, a little art, a lot of mysteries

At normal brewing temperatures (195 and above (?)), the coffee grounds release acids, oils, and several other chemicals. By cold-brewing, these are not released into the final coffee. I've read nothing which defines what temperatures are significant for the various compounds.

Espresso coffee is made by forcing very hot water through a compacted volume of ground coffee. I'm told the temperatures are the same 195-205 of standard brewing but, on reflection, that can't be true. Steam is obviously present in an espresso machine and, at sea level, steam is always over 212 degrees. This suggests that espresso is getting something a bit different from the ground coffee ??

The brewing process is a "chemical extraction", not the more common dissolving of materials into water to make a solution.

I've heard it said that plastic can sometimes alter the material stored in it (so lately I'm using glass).

Possibly important notions

Definitions of things which might matter - plus typical values, reasoning.
ratio (coffee grounds to water, by volume)
eg: "1:5" (meaning 1 volume coffee grounds to 5 water). Some of the cold-brew articles use 1:4 but my 1st attempts were at 1:5 and I've arbitrarily maintained that. (The ncusa link claims they use a 1:16 proportion but several believe they confused quarts and gallons. I made the 1:16 and it looked like colored water.)
concentrations. These 2 claims were for hot-brewed coffee! :

"use 12 grams of coffee for 6.5oz of boiled water" from 
here.

This results in a ratio of 1:5 coffee grounds to water (by volume). "Coffee should be brewed for 4.5-5 minutes using a ratio of 55 grams of ground coffee per liter of filtered water (195-205F). It is convenient to use 2 tablespoons of coffee per 6 ounces of filtered water" from here.
This results in a ratio of 1:6.3 coffee grounds to water (by volume).
water
filtered vs. tap
vessel material
plastic or glass.
vessel size
This is how much the vessel holds. I convert common units to mL (milliLiters)
total volume made
was vessel filled? has air volume?
coffee company
Peet's, Folgers, whatever
coffee roast
Some coffees are only labelled something like "dark roast" without revealing much about what kind of beans were really used. It's important, however, to record whatever the label does say so for later purchases.
coffee grounds
bought as grounds or beans? how finely ground.
initial temp
This is the water temperature when initially mixed with coffee. _Something_ in the brewing method is temperature dependent and this initial temperature may be an overlooked variable.
temperature during brewing
This is your guess about what temperature(s) the cold-brewing coffee experienced during the brewing. There may be a difference if the container was in the 'frig vs sittin on a room temperature kitchen counter.
stirring
The high concentrations of grounds to water, eg 1:5 etc, invariably mean the grounds will all clump together during the brewing. It seems plausible that grounds inside the clump may not contribute as much as those which are more exposed to the water. So carrying the vessel in the trunk of a moving car might mix the grounds and water better.
brew time
how many hours the water and grounds were in contact. 12-24 is recommended in the literature.
final volume
#cups of cold coffee liquid produced after filtering.
dilution
How much did you dilute it, if applicable, before serving. 1:3 would mean you added 3 parts water to each part concentrate.
serving temp
I think this needs should be the same as the temperature made by your hot-brew method which is likely just your coffee maker. Ours makes coffee at 135 degrees.
observations
Anything noteworthy about the brewing process
results
What you and others thought of it, compared if possible to some available standard made the traditional (bot-brewed) method. Consider using the 1-10 scoring values defined as 'Ratings' in: coffeeTasting.html.

Useful numbers

Common temperatures to know, in degrees F:
 58 tap water temp (Jan 2010)
108 hottest water from our tap. (Jan 2010)
135 temp of coffee from our coffee maker.
150 lowest serving temp seen at corporate coffee houses.
175 temp of coffee as served at Peet's. Max temp to avoid Scalding Law (?)
195 temp needed for brewing instant coffees (? from VIA instructions)
202 purists aim for this temp water to pour thru grounds for cuppings.
205 max temp Peet's brews at. (195-205).

Coffee, beans or ground, is sold by weight but you use it by measuring
out volumes. So you'll need to know that 1/2 pound of ground coffee
has a volume of 2.75 cups (measured by me) or:
82.1 grams / cup of ground coffee Be careful when using 'cups'. The modern coffee cup is sometimes much larger than the standard of measure 'cup'. 1 cup = 236 mL // standard liquid measure. 1 quart = 4 cups = 944 mL; 1 liter = 1000 mL = .264 gallons 1 oz = 28.34 grams, 16oz = 1 lb. for normal coffee brewing at 39pw, we use 4.7 cups water to .65 cups of ground coffee. That gives a proportion of 7.2 units of water for each unit of grounds, or 1:7.2 Our normal coffee maker output is around 1100mL, or 4.7 cups. The orange-topped 'Mason jars' can take 1.18 cups grounds and 5.9 cups of water. That gives 1:5. These volumes are 1.27 x the values for our normal coffee maker - but in 1:5, not 1:7.2 The Mason jars, using the 5.9 cups water to begin (and the 1.18 grounds) produces about 4.7 cups of cold coffee after filtering. A better filtering process could extract more from the still wet grounds. Our microwave heats with the following times, temps:
cupsStart
Temp
Ending
Temp
MinutesComments
5.9 58 94 5.0 tap temp
5.9 94 137 3 more  
4.7 63 137 7  
So, it appears that the contents of the large 'Mason jar' should be
heated for about 7 minutes (assuming the mason jar was full and its
temp starts at about 58 degrees).

Issues being studied, conclusions when made

- initial temperature. Do properties vary wwith different temps?
- whether to stir, shake during brewing.
- how to speed up filtering.
- material type of brew container. Is plasttic better?
- do some types of coffees (like Yuban) jusst 'not work' ?
- should we be diluting the results?
- what's the cost of these coffees?

My 'Lab Book', records of past attempts

date:  Jan 15th, or so
ratio:          1:5
water:          cold, filtered thru refrigerator's filter.
vessel mat'l:   thin plastic, a large fizzy water bottle.
vessel size:    1.25 or 1.35 quarts
volume made:    same as what we get from coffee maker, about 1100mL
coffee company: Peet's
coffee roast:   French Roast
coffee grounds: beans, ground with small grinder.
initial temp:   high 50's probably
brewing temp:   room temp (a little over 60 avg)
stirring:       I moved the bottle around occasionally.
brew time:      20 hrs.
final volume:   not measured
dilution:       none.
serving temp:  not recorded but seemed equal to hot-brew 
observations: The walls of the plastic jar caved in over the span of
   a few days while sitting in the 'frig. I don't think the size of 
   the 'dent' was too large to be explained by just the lower 
   temperature.
results:       "WOW, how smooth!". David Hicks and I had the same reaction

date:  Jan 17, 2010, the day before the tasting party.
ratio:          1:5
water:          filtered
vessel mat'l:   glass
vessel size:    1400 mL or 1.27 x the amount made by our coffee maker.
volume made:    full
coffee company: Peet's
coffee roast:   French Roast
coffee grounds: beans ground
initial temp:   water from frig's filter.
brewing temp:   no attention paid. maybe avg of 65.
stirring:       none. grounds had floated to top.
brew time:      24 hrs (?)
final volume:   not measured
dilution:       none.
serving temp:   I microwaved it. probably was 110 ?? people complained that
    it wasn't hot enuf.
observations:   none
results:        disappointing. bland


date:  Jan 20th, 6pm
ratio:          1:5
water:          filtered
vessel mat'l:   glass. same as for party
vessel size: 
volume made:    5.9 cups water + 1.2 cups ground coffee.
coffee company: Seattle's Best.
coffee roast:   French Roast
coffee grounds: beans ground in our little grinder
initial temp:   105, roughly same as hottest tap water.
brewing temp:   mid-60's
stirring:       stirred thoroughly at start.
brew time:      24 hrs
final volume:   4.7 cups
dilution:       none at start. will experiment.
serving temp:   135
observations:   grounds packed together at top of jar when brewing done.
   Stirring semi-vigorously puts a light brown foam atop the dark liquid.
   Light brown like seen on espressos.
results:        yea! very smooth! wonderful! a rating of '8'.

French Market, Jan 21

date Jan 21st, 3pm
ratio 1:5
water filtered
vessel mat'l glass. same as for party
vessel size
volume made 5.9 cups water + 1.2 cups ground coffee.
coffee company French Market
coffee roast Dark Roast, with chicory
coffee grounds was already ground.
initial temp 105, roughly same as hottest tap water.
brewing temp mid-60's
stirring stirred thoroughly at start.
brew time 25 hrs
final volume 4.2 cups
dilution none at start. will experiment.
serving temp 135
observations results

Feb 10,2010

Made 3 jugs, Sumatra, Kenya, and French Roast. No problems with taste etc even though I drank them over the course of a week or so. Very smooth. Had the still typical hassle in filtering. Tried paper towels in a colinder; that worked pretty well but didn't remove the finest grounds.

Links

Here's some background information on cold-brewing:
liquid measurements conversion chart(s) for liquid measurements.
NY Times 1/3 cup medium ground coffee to 1.5 cups water (1:4.5), cover, wait 12 hrs
ineedcoffee 1:4 ratio
Nat. Coffee Assoc. 1 cup grounds to one gallon water (1:16), 12-24 hours, filter. article describes history, oil and acid differences.
Toddy requires special, patented coffee maker.

file: projects/coffee/coldBrewNotes.html,