Wednesday, September 29, 2010

The French Press Shake

Agitation in French press extraction seems to be largely unexplored. We tried some serious agitation in the press this week, and enjoyed some very tasty results with our Koke. In addition to significantly increased extraction, the coffee tasted noticeably cleaner than even via the traditional Coffee Catcher method.

For the record, here's the process we used:

1. If you tend to use a finer French press grind, coarsen it up a few notches. On our Virtuosos, we found 27/26 led to over-extraction, and 31 was about right.

2. Use a half dose in an 8 or 12 cup press, in order to leave room for aggressive agitation.

3. Throw in a Coffee Catcher, pour and let brew stand for 3 minutes.

4. At 3:00, begin shaking the press vigorously in a consistent, circular motion. You should see a substantial whirlpool effect.

5. Shake continuously until about 3:45, and press at 4:00. Pour out right away.

So, would 4 minutes of continuous agitation inevitably over-extract? What about agitating during the first minute, instead of the final minute? There's room for more experiments here...

Monday, September 27, 2010

The Coffee Catcher Pull

I realized I hadn't yet written a single description of the Coffee Catcher Pull technique (a.k.a. the French Pull). This technique is referenced in a recent Seattle Weekly review, in an older Why Not? Coffee post, and in a previous post on this blog.

Here's how it works. You can see a video of the pull itself starting at 1:10.

1. Place the Coffee Catcher into your press, aligning the catches with the spout, and add coffee and hot water as normal. If you're using an 8 or 12 cup press, brew a half press of coffee. Otherwise, you will not be able to hook into the disc through the hot coffee!

2. Shake, submerge or stir in the coffee bloom according to your preferences.

3. After about 3 minutes and 30 seconds, gently insert the hook into both catches of the disc. This may take a few seconds. At about 4 minutes, pull the Coffee Catcher up through the brew and remove the cake.

4. Wipe the lips of the carafe with a tissue, and drop the plunger to trap any stray floaties.

5. Pour and enjoy!

Coffee Catcher FAQ

This post is long over-due! Here are the top questions we get about the Coffee Catcher. We'll update this post periodically with new questions, or info on new brewing methods (see #3 below).

1. Q: Where can I get a Coffee Catcher?
    A: Right here. Unless you live in Seattle, we are not yet in a store near you. If you do live in Seattle, you can pick up a Coffee Catcher at Trabant or at Visions Espresso.

2. Q: What is the Coffee Catcher made of?
    A: All parts are made of 100% stainless steel.

3. Q: What does the Coffee Catcher do?
    A: Two things. First, the Coffee Catcher collects grounds for easy removal after brewing. Second, the Coffee Catcher seems to filter suspended fines out of the brew in such a way that the resulting coffee tastes cleaner and has a longer cup life. Yup, that claim sounds far-fetched. We didn't believe it either at first. Posts exploring the filtration effect herehere and here.

4. Q: How do you use the Coffee Catcher?
    A: We originally designed the Coffee Catcher to be placed in the bottom of the press before adding coffee. After brewing and pressing, hook into the disc to remove the Coffee Catcher. Original video  here.
    That said, it turns out the Coffee Catcher offers intriguing possibilities for other brew methods. See experiments with coffee siphon pots, the Coffee Catcher pull technique (referenced in 5th paragraph here), and the Double Coffee Catcher technique (videos here and here), and a technique called multi-bed brewing (blog posts here and here). We expect to discover still other ways to use the Coffee Catcher in the near future. Stay tuned...

5. Q: How do I clean my Coffee Catcher?
    A: Daily, clean in three steps:
         1. After removing the coffee puck, use the hook to scrape the puck into the trash, the compost, or over your plants.
         2. Then give the disc a rinse under the faucet.
         3. Next time you brew, insert the Coffee Catcher and add a little hot water to pre-warm your press. Shake the press gently to agitate any stray fines caught between the Coffee Catcher discs into the water. Dump the water into the sink and brew in your pre-warmed press.

          Occasionally, do a thorough cleaning:
          1. Gently unscrew and disassemble your Coffee Catcher using a flathead screwdriver. We recommend disassembling directly into a bowl.
          2. Cover parts with hot water and a dash of Cafiza powder (eco-friendly phosphate free powder here)
          3. Soak for 15 minutes, rinse in cold water and reassemble when dry. To condition the metal, you can soak the assembled Coffee Catcher in water for an hour afterwards.

6. Q: I see wrinkles around the edge of my Coffee Catcher mesh. Does it still work?
    A: Yep! First, the steel discs themselves provide sufficient structure to lift and compress your coffee grounds into a cake. Second, our taste tests tell us that suspended fines trapped by the Coffee Catcher stay trapped regardless of wrinkle appearance or arrangement, perhaps because falling french press fines plug any gaps caused by wrinkles very early in the brew cycle.

7. Q: Why is the Coffee Catcher a disc instead of a cup shape?
    A: Preferences for coffee amounts used in brewing vary, and doses may even change slightly depending on roast or type of bean. We designed the Coffee Catcher as a disc in order to trap any amount of coffee: half presses, full presses, even double-dose presses (see iced coffee post here). Also, a disc shape means the Coffee Catcher will not interfere with the French press plunger action.

8. Q: Does one of the Coffee Catcher sizes fit my press?
    A: Probably, since we designed the Coffee Catcher to fit the most popular French press models. That said, let us know if you have a size that doesn't fit, as we're already working to add more sizes to the line-up.

French Press Fines

This post is a loose follow-up to the cliffhanger at the end of my long and headache-inducing post on the chemistry of French press foam.

After concluding that French press foam might act as a sort of chemical scrubber for coffee fines (insolubles), I was eager to start comparing different methods for removing fines from the brew.

While I stand firmly with those who hold the palate as the final judge of coffee quality, the palate is inevitably subjective. I set out to measure suspended French press fines concentrations objectively -- and [SPOILER ALERT] probably failed to do so.

I prepared coffee in five different ways. First, I prepared coffee traditionally, brewing in a French press for 4 minutes and shaking in the coffee bloom at 3 minutes. After that, I tried the Wendelboe / Hoffman technique, the Coffee Catcher press technique, the Coffee Catcher pull (referenced here and here), and the double Coffee Catcher technique (videos here and here).

Referencing a video at The Other Black Stuff, I decided to pour the prepared coffee in each case through a clean paper filter and weigh the results using a gram scale.
The remaining residue looked pretty scary!
After weighing the filters, I found the following (per approx. 900 ml of liquid coffee):

Traditional - 3.1g
Wendelboe/Hoffman - 2.7g (-13%) (56 g solids removed)
Coffee Catcher Press - 3.0g (-3%)
Coffee Catcher Pull - 2.8g (-10%) (103 g solids removed)
Double Coffee Catcher - 2.3g (-26%) (134 g solids removed)

Did these numbers surprise me? Yes and no. Yes, in the sense that the results are not necessarily correlated to my palate's perceived cleanliness of flavor (which I assume is a direct correlation to suspended insolubles). My palate tells me all four variants are cleaner than the traditional press, but I would have rated the Coffee Catcher Press method as substantially cleaner than the number would indicate.

However, I wasn't surprised if the results reflect heavier, non-suspended particulates. This, I think is the "mud" that sinks quickly out of the brew, and I suspect it is not related as closely to perceived cleanliness. I noted that the three methods that involved the removal of large particulates easily beat the other two methods. Also, the only double-removal method tested removed far more weight than other methods. It's worth noting that the Coffee Catcher Pull measurement is skewed slightly by experimenter error: the disc slipped slightly part way up the carafe and leaked an unknown amount of solids back into the brew.

Is any of this significant? I'm still working on that one. I set up the test hoping to test differences within tolerances of a tenth of a gram. I was careful to test as large a volume of coffee as possible in order to exaggerate per ml differences. My statistics knowledge is rusty, but preliminary results indicate that these results are not necessarily significant (i.e. differences in weights could be chance alone). My instincts disagree with this assessment, and I'll post more as I discover more.

Finally, I'm circling back to square one. How do I measure suspended French press solids? This experiment shows that they appear to be too light and/or too small to be measured via paper filters. As an example, notice the tiny residuals that leaked through the paper filters on the drying plate. A smear like this leaked through the drying filters in each case. Perhaps these are the particulates I'm hunting for.
A dry smear of particles too small to be trapped by the filter. Are these the elusive suspended solids?

Friday, September 17, 2010

The Chemistry of French Press Foam

I used to think that foam at the top of a French press was a matter of personal preference: some drinkers prefer foam's texture and astringency, while others insist it clouds the palate and inhibits flavor clarity. What does it matter? It turns out that the presence or absence of foam during the brew cycle may affect the final flavor of the brewed coffee itself.

Here's why:

Coffee beans hold deposits of fatty acids (lipids) that are released during extraction into the brew. Lipids are all hydrophobic, so in the press you'll notice them separating themselves from the water and gathering in small pools of oil at the top of your cup. 

Certain lipids also have special chemistry that makes coffee foam possible. Sterols make up only about 2.2% of the total lipids in the bean, but they are amphiphilic, which is a fancy way of saying the sterol molecule has one end that likes water (water soluble) and one end that hates water (water insoluble).

A sterol is a physically flat molecule with an hydroxyl (HO above) group bonded to four ring structures of carbon known collectively as cholestane. Chemically, sterols are part of the steroid family and are related to hormones like testosterone and estrogen. One of the sterols in coffee is cholesterol.
Amphiphilic chemicals are a must for forming bubbles, as their opposite ends allow them to line up and form bubble walls that are insoluble on the outside and soluble on the inside. As carbon dioxide bubbles form during brewing, amphiphilic sterols effectively give water-hating oils a place to hide - within the walls of forming bubbles. 

Here's the kicker. Extracted coffee oils collect against the super fine coffee grounds that are suspended in the water. Some of those fines then get trapped inside bubbles as a part of the foam structure on the top of brewed coffee. In other words, the foam on top of a press likely acts as a chemical scrubber, stripping away fines suspended in passing convection currents and holding them in the foam structure itself.

Does any of this make a tastable difference? Yes. Expert baristas Tim Wendelboe and James Hoffman have popularized a French press variant in which foam is scooped from the surface prior to pressing the coffee. Video here. The resulting brew does taste significantly cleaner and less muddy.

Photo by Alex Negranza of Why Not? Coffee

To my knowledge, no detailed chemical explanation of the Wendelboe/Hoffman variant has been proposed before. One physical explanation has been suggested: saturated coffee grounds at the top of the press over-extract when forceably moved through the brewed coffee by the plunger. The theory goes that the Wendelboe/Hoffman technique removes these grounds and thus avoids over-extraction.

On close examination, I don't think that explanation holds up. While physical agitation does increase extraction rates, both traditional methods and the Wendelboe/Hoffman brewing variant involve gentle but significant agitation when the crust or bloom is stirred in (known as the break). After the break, relatively few grounds are left floating at the top of the brew and pressing is a gentle process in both cases. In other words, most particle agitation -- and thus over-extraction -- would occur in both methods. Furthermore, over-extraction alone does not explain the significantly cleaner mouthfeel yielded by the Wendelboe/Hoffman variant. It seems like the only significant difference between the two methods is the treatment of the foam after the break.

To me, French press foam chemistry provides a much more satisfying and robust explanation for the significant cleaning effect of the Wendleboe/Hoffman brewing method. By removing foam before pressing, fines that would otherwise be agitated out of the foam and into the brew during pressing (press with foam, and look at the difference in foam color and structure before and after pressing. Where did the brown color go?) are safely removed from the brew and from your cup.

So how does the Coffee Catcher - a physical fines filtration system at the bottom of the press - compare or contrast with the chemical scrubbing process that I've suggested lies behind the Wendleboe/Hoffman technique? I've been tasting both and thinking hard about both - and the results are for another blog post!

This post depended heavily on a number of sources, particularly James Hoffman's excellent 2006 post on coffee chemistry.

Here are a few further reading links:
Sterols article at Wikipedia
Sterols and their Conjugates, at the Lipids Library (useful for understanding esters of sterols)
Cholestane stub at Wikipedia
Discussion of the Wendelboe/Hoffman technique at
Chemistry of Soap at (soap is also amphiphilic)

Finally, one interesting theoretical question for extra credit: esters of sterols make up another 3.2% of coffee lipids. Esters, in my very limited understanding, tend to be inert. If so, does the brewing process break down these esters, releasing free sterols that form foams? If not, do esters of sterols contribute to bubble formation regardless?

Wednesday, September 1, 2010

Five French Press Faux Pas

I love that rhyming title! The French press is a relatively undemanding coffee brewing process. It's hard to screw it up. That said, there are a few sure-fire ways to extract bitter coffee from your press.

Here are my top five:

1. Leaving coffee to sit in the carafe after the plunger is pressed down. Coffee will keep brewing through the screen, resulting in a bitter and over-extracted second cup.

2. Brewing with boiling water. You'll burn your coffee. It won't taste good. Don't do it. To be safe, let boiled water rest for about a minute before brewing. Advanced brewers may wish to tweak brewing temperature by adjusting the height and thickness of the poured water column. Pouring higher and thinner cools your water faster, and vice versa.

3. Over-brewing. The French press is forgiving, but it's patience is not infinite. Over-extraction will occur if you let the coffee sit. A good rule of thumb is to aim for three to four minutes contact time between grounds and water.

Some tired drinkers over-brew in a misguided attempt to jack up caffeine content. Proper brewing extracts the vast majority of the caffeine in the bean so brewing super-long only makes your coffee taste bad. If some morning (or evening) you do need an extra jolt, simply increase your grounds-to-water ratio at the start of the process. Dark roasts, by the way, do not contain more caffeine than light roasts. Since roasting does not destroy caffeine, the jolt per bean remains the same.

4. Using too little coffee. Home-made coffee bought from a local roaster costs less than a dollar per cup, so don't skimp on the coffee! Most presses ship with little black scoops that hold seven to eight grams of coffee at a time. Use about eight scoops for a 32 oz press, or four scoops to make a half press. A low coffee-to-water ratio yields an over-extracted, bitter cup -- even at a regular four minute brew time!

5. The microwave. Never re-heat coffee! It tastes terrible and savings are negligible. Instead of making a large batch of coffee in the morning, take a mini coffee break and brew by the cup. Your coffee will be tasty every time, and the mini breaks will help to keep your head clear as well.

Friends Don't Let Friends Reheat Coffee!