# Water with Aeropress experiment



## Earlepap (Jan 8, 2012)

A while ago I conducted a somewhat slapdash experiment comparing bottled mineral water to London tap water. I pretty much drew no conclusions but the variables were all over the place so any I might've made wouldn't have been too useful.

Today I thought I'd repeat the experiment but get as close to scientific accuracy as is possible with the basic gear most of us have.

I made three cups of coffee, back to back. Of course it would be great to taste side by side, but then the temperatures would be all over the place.

- 1 cup London tap water, 1 cup Brita Maxtra filter (brand new cartridge) and 1 cup Volvic bottled water (considered the best mineral water for coffee it seems).

- I used an Aeropress which of the brew methods available to me, is the most repeatable/consistent.

- 15g dose of Has Bean Nicaragua Limoncillo Washed roasted 25/05 (cupping notes - toffee apple), ground to a coarseness slightly finer than I'd use for a V60. I chose this fine as the Vario is not as consistent a grind the coarser it gets.

- 750ml of water taken to boil each time, and left cool for 30 seconds.

- 200ml poured into inverted Aeropress, stirred 4 times, left to steep for one minute, stirred twice, then plunged through one rinsed filter over 30 seconds until hiss begins.

I've no TDS meter or refractometer so results were based purely on taste alone and compared mentally to the best Aeropress' I have tasted using beans of equal quality and prepared with Uber boiler and grinder.

Tap water:

Visible milky 'slick' on top of the cup when tipped towards light. In taste slightly muddy and muted. Certainly get some apple acidity and toffee sweetness but not much. Medium body and mouth feel. A touch of bitterness on the after taste.

Brita filtered water:

Less visible impurity in cup, but still a small amount. The acidity and fresh fruity notes are far more obvious. Sweetness however seems to have nearly vanished, and there is less body. No bitterness.

Volvic water:

Little to no visible defects, any apparent are probably from kettle scale (though I descaled less than a week ago). Again the acidity is far more accentuated, but even less sweetness and body. Tastes 'thin' and frankly one dimensional.

Unfortunately at this point I burn my tongue and can no longer taste much so have to call it a day.

Conclusions (conjecture?):

Each brew was under extracted. However this was a test of water quality and it's effect on the cup so I don't think the experiment was entirely useless. From tap to Volvic the cup did become far cleaner tasting overall, and the fruity acidic notes were more apparent. From the first cup of tap water brew, I thought it might actually be over extracted due to the bitter touch. It seems however that this bitterness was coming from whatever crap is in the hard as nails East-End London tap water. Having said that the tap water was by far the sweetest and most full bodied of the cups making it arguably had the most balanced. In truth if I had tasted each side by side, I would have probably chosen the tap water as my favourite, despite lacking the clarity of the other cups.

This is not to say I'll be only using unfiltered water from now on - on the contrary. It's widely and understandably considered that filter water is best, but it's interesting to see the massive impact water quality can have on a brew, and how confused it can make everything. Tomorrow - should my tongue regain the ability to taste - I'll repeat the experiment with different brew parameters. I think the grind and dose are fine, so I'll probably up the steep time. Since I was able to burn my tongue I think perhaps the water temperature was too high as well - maybe scalding the coffee, muting the flavours? - so I'll do another set with the kettle left off the boil for longer. That's if I have enough coffee left.

I'd be interested to know the results anyone with an IMM sub and a refractometer (looking at you Mike) have following the same parameters as me. If anyone has bothered to read all of this, I hope it's not been a complete waste of time. One last thing: proof of how buggered my taste was from the tongue scalding, came after the experiment where I ate some particularly stinky washed rind cheese on bread, but could've been munching sawdust on Rivita for all I knew.


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## MikeHag (Mar 13, 2011)

This is great, Rowan. Love it. I have been intending to do all kinds of similar things recently, with various different bottled waters, but haven't had the time. Anyway, I guess my main thoughts are as follows:

1. Brita filters. If I understand their technology correctly, then I think we should all be cautious of using them for coffee. The seem to use ion exchange, which basically takes the water TDS down by replacing positively charged ions (mainly calcium) with negatively charged ones (sodium). The problem with this is that the sodium binds with the bicarbonate already in the water, and the sodium bicarb adversely affects the extraction, making the coffee astringent and bitter. That's the theory, but I haven't tested it myself under controlled brewing conditions.

2. It's possible that you're getting bitterness from the brew water being hot. I used to find the Aeropress bitter until I went down to 80C. I just mention it because it's a parameter.

3. Apples and oranges. Because the three waters are chemically different, they will extract different solubles at different rates. Therefore, if you follow exactly the same brewing process with all three waters, you will end up with a different TDS and Extraction Yield in the cup, and therefore each will taste different due to the extraction, rather than due to the water itself. To compare apples and apples you would most likely need to use a different grind for each different type of water, so you achieved the same extraction. Fair enough though... without any way to measure the extraction it's tough to create an environment where you can compare apples and apples, and the experiment is definitely worthwhile.

4. Tasting temperature. I'd say definitely leave it until the coffee is around 65C max before drinking, otherwise all you taste is hot, and once the tongue has been slightly scalded it doesn't work. Just my view.

I am surprised by your tasting results... volvic should indeed taste the better of the three. But like I say, maybe the volvic brew was underextracted and the tap water wasn't. That would surprise me though, as the tap water in London has high TDS so if one of them was going to be underextracted I'd have thought it would be that one. I've had my doubts about volvic for a little while anyway. It has a bicarbonate level of 258mg/L (if that website is still accurate), whereas the SCAA 'ideal' is only 40mg/L, and no more than 100, so 258mg/L of bicarb (alkilinity) will neutralise all those aromatic acids in the bean, theoretically killing off the nice aromas and flavours and leaving a fairly bland coffee. Try Highland Spring. It has better chemical stats.

I'd say try again with a finer grind and see if you get the same results. My Aeropress grind is finer than my single cup pourover grind. Inbetween that and espresso. It needs a 15-20 press to reach the bottom due to the resistance of the grinds. With a different extraction caused by a finer grind you may completely change your water preference.

Nice one


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## garydyke1 (Mar 9, 2011)

I wonder if using Volvic instead of my regular Brita tap water is the cause of horrid tasting espresso with Unkle Funka, Volvic should be good for espresso with a ph7 and bang on TDS. Its doing my head in, lol


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## JamesG (Mar 29, 2012)

Perhaps the lower tds = hungrier water rule is an over-simplification. Maybe water is pickier about what it dissolves, trying to reach/keep some kind of equilibrium.


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## MikeHag (Mar 13, 2011)

JamesG said:


> Perhaps the lower tds = hungrier water rule is an over-simplification. Maybe water is pickier about what it dissolves, trying to reach/keep some kind of equilibrium.


Exactly. I think there's a general kinda blurry understanding that all that water washes coffee particles from the grinds... i.e. purely a physical action... but there is also a chemical action going on, and the water chemistry dictates which of the (approx) 1000 different compounds in the beans it will will dissolve. Looking at TDS alone is very simplistic. We can look even closer (i.e. break TDS down into its calcium element, which has a significant impact on extraction and flavour), or go broader and look at other constituents of the water... pH, as Gary mentions. Also chlorine, which is a disaster for coffee if it is present in the water... sodium... alkilinity...

There's no getting around it. These things do affect extraction and taste. But because they are tough to get our heads around, they are almost universally ignored in the vain hope that they won't matter. As baristas we spend so much time on effort on so many areas, and I'm sure we would spend more time and effort on water if someone made it easier to understand. The Water Quality Handbook has helped me, but it isn't an easy read. Personally I think the SCAE should conduct its own up-to-date experiments regarding the effect of water quality, and publish the results along with a new book explaining it all in an easy to read manner.


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## Earlepap (Jan 8, 2012)

MikeHag said:


> Apples and oranges.


Bugger!

Interesting feedback Mike, cheers. I'll try again with some Highland Spring and definitely lower the temperature. Roughly how long off-boil would you say it takes to get water sat in the kettle down to 80c? I do have an electric thermometer, but I calibrated it myself and therefore don't really trust it one bit, but it's worth a look I suppose. As for the temperature when tasting, I'll definitely let it cool more since I don't want any more tongue scalding.


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## MikeHag (Mar 13, 2011)

I just did a test. It took over 3 mins of fairly active swirling to reduce the temp from boiling to 80C... that was 1 litre.

So I then worked out that if you add 200ml of cold water to 1L, it reduces to approx 80C... much quicker.


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## JamesG (Mar 29, 2012)

MikeHag said:


> Personally I think the SCAE should conduct its own up-to-date experiments regarding the effect of water quality, and publish the results along with a new book explaining it all in an easy to read manner.


I agree. We appear to have lots of hypothesis on coffee but no one (publicly) is designing experiments to prove them.


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