It's real, it's debilitating, but your shrink will tell you it's all in your head.
mitch236 Said:
Since my setup underextracts no matter how I try to manipulate it comes down to one of two issues: Either my water has too low TDS (it is 50 ppm) Or my machine's pump pressure is too low (it is currently set just below 9 bar by the integral pressure gauge which could be wrong)
At one point my pump pressure was too high (by about 2-2.5 bar). When I got the pressure down, the extraction yield went up by 2%.
Also, I've found that in a VST basket, using a 58.4mm flat tamper gives about 0.5% higher yield than a 58.0mm flat tamper.
My experience indicates that low yields may be caused by multiple factors. The refractometer allows you to test each factor more-or-less in isolation. The effect of experimenting with each brew parameter individually may not be tasteable, but it may easily be seen with the instrument. Then, when you put all the optimizations together, you can end up with a big improvement in your brew. Optimizing each brew parameter without the refractometer would be very difficult and take ten times as long.
mitch236 Said:
I'll know the answer to the pressure issue tomorrow morning. The water TDS issue will be dealt with in a few weeks.
50ppm does sound quite low for brewing coffee/espresso.
mitch236 Said:
Bottom line: If you can easily afford one, get it. Yes, I've heard the complaints about the filters being expensive but in the grand scheme a dollar isn't really much money.
The cost of filters is annoying but an unfortunate necessity when measuring metal-filtered coffee (espresso, french press, Coava Kone, etc). The filters are not necessary with paper filtered coffee.
You'll feel better by thinking of the coffee you save every year by extracting at 19% instead of 15-16%. It adds up.
Posted Fri Mar 9, 2012, 7:45pm Subject: Re: coffee refractometer
Curiouser and curiouser...
Well known recipe for me, 22g coffee:230g water, I went a touch smaller on the grind. JUST off boil - as in 210°F when stirred once, and 3:15 steep.
Filtered twice for fines (very low, less than 0.1 g), and got a wet puck of 49.3g, and 199.6g of coffee. Just as expected, with a respectable 4.5g of loss (not surprising, evap in the first few minutes is a good chunk of this, actual measured brew water was 231.4g).
Expecting 2.20% strength - smells right. Looks right. Actual measured is 1.95% (1.93-1.96).
Back-calculating is 3.89g TDS, or 17.7% extraction. Low? 3 minute contact time on a fine grind with boiling hot water? Fishy to me.
We'll see. Yep, I zeroed with distilled water. I may have to get the calibrating solution (another $50) to make sure the span is correct.
Puck and the beverage is in the oven. I've done this brew several times, and the dried coffee is almost always 17.1 to 17.7g, and the times I've dehydrated the beverage have always been over 4.0g.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Fri Mar 9, 2012, 8:01pm Subject: Re: coffee refractometer
Very useful, though - repeatability is remarkable. It looks like a DC offset if this is off. Just tried a 2nd cup, 3:30 steep time, finer yet grind.
203g coffee produced, 1.94% strength. Multiple measurements 1.93-1.95%. But that 17.9% extraction? It SURE DON'T taste like it. Sipped a little, then diluted 190g of the coffee (still at 1.94% strength) to 300g total. This tastes strong for brewed coffee, I estimate close to 1.35%, but the VST says only 1.19-1.22%.
So, the VST seems to be measuring dilution fairly correctly (as far as the accuracy goes).
190g @ 1.94% => 3.686g TDS
Add water to 300g
300g @ 1.20% => 3.600g TDS (pretty close)
Or, maybe mine particular unit just has an offset or percentage off.
Dry, darn you! Dry!!! LOL
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Have you tried repeatability when making multiple measurements of the same coffee interspersed with measurements of water? It may be doing some sort of averaging. In fact, I've just checked the VST website and it explicitly states that it automatically averages multiple readings.
Looking forward to seeing your dehydration results.
Posted Sat Mar 10, 2012, 6:16am Subject: Re: coffee refractometer
Netphilosopher Said:
Expecting 2.20% strength - smells right. Looks right. Actual measured is 1.95% (1.93-1.96).
Back-calculating is 3.89g TDS, or 17.7% extraction. Low? 3 minute contact time on a fine grind with boiling hot water? Fishy to me.
We'll see. Yep, I zeroed with distilled water. I may have to get the calibrating solution (another $50) to make sure the span is correct.
Puck and the beverage is in the oven. I've done this brew several times, and the dried coffee is almost always 17.1 to 17.7g, and the times I've dehydrated the beverage have always been over 4.0g.
The Aeropress filters pass a significant amount of fines. Your evaporation technique counts these fines as dissolved solids, whereas the refract does not. If you could filter your beverage with a sub-micron filter, and then evaporate, I suspect your result would be more in line with the refractometer.
It would be interesting if you could use your current brewing technique to get your extraction yield, as measured with the VST, up around 19%. Then how does it taste?
The current center point for taste preference is assumed to be 19%, with a plus/minus factor of 1% or 2%. You are actually not that far off at 17.7%, but you just might prefer the beverage at a somewhat higher extraction yield.
I recently heard a story that is relevant. Bear in mind that I got the story 2nd or 3rd hand, but I have no reason to suspect it's untrue.
A certain former Barista World Champion, known for his excellent coffee roasting, was visiting another former Barista World Champion. The municipal water at the first guy's location is known to be very low in TDS, whereas the second guy's is relatively average. When the first guy tasted his own espresso blend at the second guy's shop, he was shocked, saying, "I've never had my own blend tasting so good!" They looked at a bunch of factors (grinder, espresso machine, etc) but concluded that the water was the reason.
Hey Mitch, one more thing. I assume your Linea is plumbed in. Well, you could buy a bunch of Cirqua formula packets and temporarily run your machine off a jug using this formula water. That's what I did with my Speedster when I was investigating extraction parameters.
Only caveats are: (1) you have to readjust the pump bypass to compensate for zero incoming pressure rather than your current incoming pressure (2) ideally you'd want to drain brew boiler first so incoming formula water isn't diluted with low-TDS water
Anyway, it would be a low-cost method for evaluating your present water supply.
An even easier thing to do would be to buy the packets and compare Aeropress (or any other brew method) coffees made with your 50 TDS water vs formula water. If your water really is a problem, both your taste buds and the refract will tell you.
Andy, putting two and two together with your earlier comment in this thread about extraction envy with the K10 vs. Robur, was this 0.5% difference from the tamper size the explanation for the 0.5% delta that you had originally attributed to the grinders?
One of your posts last fall on this difference triggered a virtual stampede on 58.4mm tampers - so I was half expecting that the K10/Robur mention here might cause thousands of Roburs to suddenly appear on eBay and Craig's List in the past few days, with a corresponding worldwide shortage of K10s. On this thread, however, it caused nary a ripple (though I can only imagine what might have resulted had it been posted on H-B...)
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