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Netphilosopher
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Joined: 14 Jan 2011
Posts: 1,602
Location: USA
Expertise: Just starting

Posted Tue Jun 26, 2012, 10:05am
Subject: Compare and Contrast
 

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jpender
Senior Member
jpender
Joined: 11 Jul 2011
Posts: 694
Location: California
Expertise: I like coffee

Grinder: OE LIDO
Vac Pot: S/S Moka Pot
Drip: Aeropress
Posted Tue Jun 26, 2012, 7:08pm
Subject: Re: Compare and Contrast: Strength and Brew Method
 

Netphilosopher Said:

I think that the pressing while hot allows more oils to get through the coffee.  Based on past observation, these oils can be quite bitter when isolated (like in centrifuging) and tasted alone.  I call them oils, but they are probably somewhere between waxy lipids and lipids that are sort of fluid at 45F.  

I suspect that pressing the brew when cold keeps much of these oils in the grounds (well, maybe a LOT of them, based on the increased mass of the spent grounds).  I also find that these "oils" when mixed hot do have a tendency to push the pH down in a solution (I've got only an indication, my cheap pH meter is pretty flakey) if you mix them into hot distilled water.

Posted June 26, 2012 link

A typical refrigerator is at a temperature pretty close to the melting point of coffee oil. But there isn't enough oil in coffee to account for even half the difference in the masses of the wet grounds. So most of that difference must be due to absorbed water.

I have a question: How does the presence of oil affect refractometer readings?
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Netphilosopher
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Posted Wed Jun 27, 2012, 7:43am
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Netphilosopher
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Posted Wed Jun 27, 2012, 8:05am
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jpender
Senior Member
jpender
Joined: 11 Jul 2011
Posts: 694
Location: California
Expertise: I like coffee

Grinder: OE LIDO
Vac Pot: S/S Moka Pot
Drip: Aeropress
Posted Wed Jun 27, 2012, 2:15pm
Subject: Re: Compare and Contrast: Strength and Brew Method
 

Netphilosopher Said:

Not sure - I thought that many triglycerides are around 60-80F crystallization temp or so?  I agree, though, if there is semi-solid triglycerides or other oils I think this will act as a physical impediment to the coffee cake, but not a significant contributor to total mass.  The press force and rate is definitely slower - see my following post.

Posted June 27, 2012 link

From what I understand the melting points of triglycerides vary widely depending on a number of factors. Many common vegetable oils have low melting points. Coffee oil is primarily linoleic acid, the same as in safflower oil which freezes below 0C. Coffee is composed of more than one type of fat so you'd expect the melting "point" to be over a range of temperatures. Despite this one researcher (Calligaris, 2009) reported measuring a well-defined melt/crystallization point (6.5C) for coffee oil.

Netphilosopher Said:

As far as I can tell, oil, at least the amount in coffee, does not seem to affect the actual refractometer readings.  I base this on 20minute centrifuged samples of coffee at maximum rate (I think somewhere around 2500 g's or so, 4000RPM medical 15ml centrifuge), where there is a clear lipid layer at the top of the sample, and I check the strength (cooled) and find it the same as just-pressed hot coffee.    In the stuff I've collected with ~180 ml of centrifuged coffee, I think it was well less than a gram in total (that took quite a while, as I only have 6 X 15ml tube centrifuge, so two rounds of spinning, separating, collecting, re-spinning with hot distilled water, etc.).

Posted June 27, 2012 link

How did you determine what this liquid was?

I believe the oil has a higher refractive index, but there might not be enough of it for your refractometer to detect. Or maybe it isn't dispersed evenly, I don't know.

Do you have an estimate for how much oil makes it into the cup when you press hot through your AP? In one study, coffee filtered through paper contained 7mg of oil per 150ml of coffee, coffee filtered through a metal screen contained 50mg per 150ml, and Turkish and espresso contained 60-160mg per 150ml. This isn't enough material to affect the wet grounds mass noticibly, but it could be affecting taste and aroma. Then again there might be more than one thing going on here.

Netphilosopher Said:

Off to the store to buy me some.... Everclear.  LOL

Posted June 27, 2012 link

:-)
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Netphilosopher
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Posted Wed Jun 27, 2012, 2:38pm
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jpender
Senior Member
jpender
Joined: 11 Jul 2011
Posts: 694
Location: California
Expertise: I like coffee

Grinder: OE LIDO
Vac Pot: S/S Moka Pot
Drip: Aeropress
Posted Wed Jun 27, 2012, 3:35pm
Subject: Re: Compare and Contrast: Strength and Brew Method
 

Netphilosopher Said:

I thought that Lockhart stated that analysis of coffee (pre and post roasting) had estimates of ~13% fat from his flavor research for the military?  That would be on the order of 2600mg / 20g coffee POSSIBLE in my case, but obviously not all of it is going to be extracted.

Posted June 27, 2012 link

Yes, that's right. Illy puts it at about 15% for arabica. But how soluble is it? It's clearly possible to extract it all; they did that to determine content. But they didn't do it by steeping it in hot water for a few minutes.

Netphilosopher Said:

Aren't the studies you reference more concerned with just the kahweol and cafestol components?

Posted June 27, 2012 link

The first one isn't. The second (Ratnayake WM, 1993) where they measured lipids in the cup does discuss the health concerns of coffee and elevated cholesterol. But they measured the total lipids, not just some components. One thing worth noting is that for paper filtered coffee they used a brew ratio of 30g dry coffee to 1 liter of boiling water, so adjust the numbers upward by a factor of at least two. Illy puts the typical lipid content of espresso about three times higher than what they reported. But the amount of oil is still relatively small compared to the bulk of the grounds.

Netphilosopher Said:

I didn't think I was getting so much that I could actually measure it with a scale - I am suggesting that some portion of the lipids or fatty acids are increasing the filtering effect of the coffee grounds.

Posted June 27, 2012 link

Maybe. But what else changes in the grounds when they're hot vs. cold?
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Netphilosopher
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Posted Thu Jun 28, 2012, 4:36am
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jpender
Senior Member
jpender
Joined: 11 Jul 2011
Posts: 694
Location: California
Expertise: I like coffee

Grinder: OE LIDO
Vac Pot: S/S Moka Pot
Drip: Aeropress
Posted Thu Jun 28, 2012, 10:36am
Subject: Re: Compare and Contrast: Strength and Brew Method
 

Netphilosopher Said:

Well, maybe the reason they absorb oils with paper filtered is that paper-filtered coffee is gravity-percolated, not forced.  (and all of the coffee in every analysis of cafestol and kahweol I've seen that is paper filtered has been gravity-percolated).  Maybe it's not the magic of the paper, it's the retention of lipids with gravity-percolation in the grounds.

Posted June 28, 2012 link

I thought that one of the reasons people use non-paper filters for the Aeropress is to obtain more oils in the cup?

Netphilosopher Said:

I see absorption for gravity perc methods vary from 1.65 to 2.3.  This includes Chemex (limited sample, but consistent), Hario, CCD, my B&D ancient coffeemaker (12 cup with a woefully undersized basket), and the Melitta BCM-4C.

Espresso, absorption varies (based on weighing wet puck with ~20% extraction normal strength presses, 8g : 30g produced around low 5% strength) but is in the low 1's (I use an average of 1.05).

Of course, Boiled coffee decoction and Press Pot aren't valid measures of absorption, IMHO.  These methods are coarsely filtered or not filtered at all, and contain significant amounts of perfectly valid coffee in the soaking wet grounds.  If I do a normal French Press on my Bodum Press, (56.25g coffee:950g Brew Water), the "absorption" is technically around 3.3!  Keep in mind the wet grounds at the bottom aren't fully pressed, either.

Posted June 28, 2012 link

What does it mean to say the absorption is "valid"?

Liquid retained is liquid retained and it depends on the brew method more than the coffee itself. For my moka pot I measure between 1.2-1.7 grams of water retained per grams of dry coffee, which is about 1.0-1.5 by your "absorption" measure (wet grounds / dry grounds - 1). But if I actually weigh the wet grounds directly as soon as I can collect them I get a much lower number, more like 0.8-1.2 absorption, because the water is evaporating so quickly. If I could measure it as soon as I poured the coffee it might be different again. So which measure is valid?

Ultimately what matters is the total loss, the liquid that doesn't make it into the cup because the grounds absorb it, it evaporates, spills, or gets trapped in some other part of the brewing device.

Netphilosopher Said:

3% brew ratio???? jeez.  I bet nearly every cup in that study (if using normal contact times) are overextracted.

Posted June 28, 2012 link

Go ahead and try to tell me that all of your coffee experiments taste great. :-)
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Netphilosopher
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Posted Thu Jun 28, 2012, 12:19pm
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