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Sep 6, 2012 02:46 PM

Can someone explain to me the science behind cafe sua da, and why they use individual filters?

I've been drinking the coffee for decades, now I want to know the science behind it.

I hear from many n00b cafe sua da drinkers that they find it "incredibly strong". Is this directly related to the filter? If so, why?

In addition, would using an aeropress provide a different flavor profile?

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  1. I'm no expert in Vietnamese coffee, so I apologize in advance if I get this wrong.

    The filter for cafe sua da should do a couple things. For one, it determines the extraction time - how long the water takes to drip into the cup. And this is one of the major determinants of the coffee's strength and body. Note that the fineness of the grind, temperature of the water, and ratio of coffee to water also all play significant roles in strength.

    One other thing it MIGHT do - it might allow a certain degree of coffee particulate matter into the final cup. This hypothetically would add body, much like a french press. But I'm not really sure if the idealized Vietnamese coffee contains much of this fine particulate coffee or not, to be honest. You can get a decent amount of body from just a very strong brew mixed with condensed milk.

    The Aeropress can easily create coffee of the same strength as cafe sua da with excellent flavor. Because of its paper filters, it may have difficulty creating a really thick body. But I'm not sure that extra body is really needed anyway. Here's a link:

    2 Replies
    1. re: cowboyardee

      " For one, it determines the extraction time - how long the water takes to drip into the cup."

      Wouldn't this also relate to how packed the coffee is? This is directly related to user interaction, so 2 cups of cafe sua da COULD taste completely different based on how tightly packed the phin is.

      I believe baristas refer to this as "tamping", and being able to do this consistently is (AFAIK) one quality of a skilled barista. I have never known ANY vietnamese sandwich shop to care this much, so am I way off base here?

      1. re: ns1

        Yes. Also whether the coffee is dampened before the main extraction. Pre-dampened coffee yields a stronger cup in any drip style of brewing because, like a more tightly packed container, it lengthens extraction.

        The Aeropress actually has the ability to largely sidestep the packing factor if you brew inverted, btw.

    2. I'm not a fan of this style, but part of its 'strong' taste is that it's generally made with robusta beans (Vietnam coffee being almost exclusively robusta) which are almost always french roasted (because a lighter roasted robusta tastes like rubber).

      I think the other part (the 'science') is that the brewer doesn't provide any headspace. Without room to expand, I would think that you'd get mostly underextracted coffee coming out.

      Best illustration is if you were making espresso and overdosed on a standard basket to the point where you'd see a deep imprint from the screw in the diffusion screen. When you try to brew the espresso that way, the initial burst of water pressure slams the grounds against the screen, effectively slowing the amount of additional water than can penetrate. This results in nothing coming out of the spouts for 10-15 seconds and then only a slow drip - no stream. The resulting shot is inky, viscous and sour.

      The Aeropress makes sense, plus you could grind finer because of the paper filter (although a metal screen filter is available). It would be wrong, however, to characterize the resulting coffee as "espresso" as that requires significantly more psi of pressure. But the Aeropress is much easier to clean. I'm surprised the article's author thought baristas would hate the Aeropress. Au contraire, they love it. There's even a World Aeropress Championship, in which many of the world's best baristas participate.

      6 Replies
      1. re: Panini Guy

        What is "this style"? Old school vietnamese phin?

        What I'm trying to do is merge old school and new school together. I got a local roaster so I'm gonna try to do cafe sua da using all their dark roasts. If I can't get something superior to Trung Nguyen next step is to ask them to roast it suuuuuuuuper dark. I just can't a cafe sua da in this town the way I would drink it (strong as hell). All I taste around here is condensed milk.

        I don't call the by-product of the aeropress espresso...I call it very good coffee (no matter what their pamphlets say)

        1. re: ns1

          Yes, the phin with screw-down filter.

          I'm going to ramble here a bit in hopes that this make sense on the "science" aspect.

          After reading more on this, a couple of things to note. Traditional drip coffee uses a 16.5:1 coffee to water ratio. It looks like for a standard 7oz CSD that ratio is 14:1, thus more concentrated. Regular drip also tastes best at a solubles concentration of around 1300 TDS and extraction (solubles yield) of 19-21%. I have no idea what the extraction is for CSD but I imagine the TDS is much higher - like 1600 TDS or so with a lower yield of maybe 13-15%. It would be usefulto measure a "well-made specimen" of CSD for a baseline.

          If I remember correctly, the Aeropress scoop of coarsely ground coffee is 12.5g while a tablespoon is 14.3 grams, thus you'd use only a hair over 6oz of water per Aeropress scoop to get the concentration right. However, because you're using the inverted method, you're doing a 'full immersion' brew, like a french press or Clever dripper. So you will not be able to duplicate the phin methodology, which is a passthrough brewer - essentially an espresso machine without the pressure.

          Because of its design, a phin simulatenously overextracts and underextracts the coffee. The first couple of ounces will be highly concentrated, the last couple not so much. Any full immersion method (press, Clever, Aeropress) will be more consistent front-to-back, maybe a little less on the Aeropress because there is some pressure involved to move the water through the puck. If you've ever 'separated shots' on an espresso machine using the Schecter method (six shot glasses on a board, capturing about 4g output in each) you'd see dramatic variations of color, thickness (TDS) and crema on each. The phin appears to brew the same way, except without the crema.

          I'm also thinking CO2 may have a role, but that's hard to prove without a lab. In most other brew methods there is a bloom that occurs from water initially hitting the grounds. CO2 is released from the beans and escapes through air, even in an inverted Aeropress. In the phin, the CO2 would have to escape through the water sitting on top of the screw-down lid. I think - but it's just an assumption - that the trapped CO2 in the coffee bed prevents full extraction of some solubles that may otherwise provide 'balance', leading to the 'strong' taste.

          Probably the only way to truly simulate a CSD brewer with an Aeropress would be to use the non-inverted method and have a second disk that fit snugly inside the tube atop the grounds, but could be pressed down along with the water. In any case, I think using the standard Aeropress method (not inverted) with a finer grind that slows down absorption and pass-through would get you closer to a CSD than what you're doing.

          I am also wondering if you can come close using a finely ground coffee in a Neapolitan (flip) brewer.

          1. re: Panini Guy

            Thanks, these are the types of posts I was looking for!

        2. re: Panini Guy

          I now use a Coava/Acme stainless steel filter in my Aeropress. The flavour and mouthfeel is closer now to French Press than if I use paper filters. It is slightly more acid and you can feel the fine grinds which give French Press that body.

          And yes - baristas here in my city love Aeropress though I do still know a number of coffee-geeks who frown upon it.

          1. re: fmed

            do you grind your beans with the french press settings w/ the metal filter?

            1. re: ns1

              I grind it finer than that. ("10"-ish on my Baratza).

        3. It's the same principle behind the French press, with a slight variation based on the Vietnamese phin filter.

          A French press brings the water into extended contact with the ground coffee, and even after the grounds are pressed down a fine sediment of coffee remains. This gives a slightly thicker taste and feel to coffee brewed this way which some love but others find distasteful compared to the thinner liquid of drip coffee.

          The traditional phin filter however is a bit different in that it is much slower – part of the charm of Ca Sua Da – and it creates a rounder mouthfeel. This is due to the long contact the beans have with the water.

          The aeropress like a French press would be different because you have less contact time with the beans.

          3 Replies
          1. re: ipsedixit

            "The aeropress like a French press would be different because you have less contact time with the beans."

            Is this true if I brew inverted and let it sit there for 10 minutes?

            1. re: ns1

              That I do not know. Sorry.

              Get a phin filter. They're cheap and very cool.

              1. re: ipsedixit

                I have one. I quit drinking CSD for a few years (after drinking them for a decade), now I'm making my return. Taking it to the next level!

                double blind taste tests are in order.

          2. Doing my own reason why drinkers may claim CSD makes them "wired" is the fact that Vietnam mainly grows robusta beans, which contains more caffeine than arabica beans (2.7% vs 1.5%). The robusta also has a more bitter finish compared to arabica beans, which make it a better fit for CSD.

            Unfortunately, my roaster does not have robusta beans :(

            3 Replies
            1. re: ns1

              The sweetened condensed milk dampens the flavors the coffee, and robusta stands up that better than arabica.

              1. re: paulj

                Agree. I find that condense milk tends to obliterate any nuances in any bean. The robusta roasts in a typical Vietnamese canned coffee brand (eg Trung Nguyen) tend to have stronger flavours and a coarser profile. And I do get much more wired drinking CSD - probably a combination to the higher caffeine content and that fistfull of sugar that condensed milk provides.

              2. re: ns1

                Funny, I find I get less wired drinking CSD than I do other coffees (espresso or drip styles) or caffeinated tea. Also seems to be kinder on my tummy for some reason. Good luck with the experiments. I'm lazy and just use the phin filter (did not know that's what it was called till reading this thread), Trung Nguyen brand ground coffee and Longevity brand condensed milk. Now I'm craving one!

              3. Okay followup question. What determines the strength of the brew, how "packed in" the coffee is (a by product of pressure via screw filter or manually pressing down via gravity filter), or the ratio of coffee/water?

                Pressure = over/under extract, Amt of water = how concentrated it is? Is that right?

                Also, for anyone curious enough, for this Little Saigon ExPat Cafe Du Monde offers the flavors that I grew up with. Trung Nguyen offers a very strong chocolate flavored coffee.

                TN is very, very different and hard for me to adjust to. This is probably due to consuming thousands of CSD's in little saigon in my late teens/early 20's.

                10 Replies
                1. re: ns1

                  Sorry if you answered this elsewhere, but if so I didn't see it: how are you brewing your coffee? With the Aeropress or the phin filter?

                  As I mentioned above, I'm not familiar enough with a phin filter to tell you anything all that technical about it. But if you're trying to futz with your results from an Aeropress, I could probably help.

                  1. re: cowboyardee

                    Using the phin right now but I will gladly take the answer for the aeropress.

                    1. re: ns1

                      First off, some review of terminology. I apologize in advance if you already know this stuff.

                      The 'strength' of a cup of coffee refers to how concentrated the solution (the drinkable coffee) is. This is pretty straightforward - you take a sip of very concentrated, dark, intensely flavored coffee and say 'wow, that's strong.'

                      The 'extraction' on the other hand - that refers to what percentage of the beans are actually dissolved in the water. In practice, this means that coffee can simultaneously be very weak, but also very over-extracted - for example, grind a single coffee bean extremely fine, pour a gallon of boiling water over it, stir for 5 minutes, and then filter.

                      Likewise, coffee can be very strong but under-extracted. If you go by the directions of the Aeropress, that's what you'll get. You're not extracting a high percentage of the bean solids, but the ratio of coffee to water is so high that you're getting a very strong brew. This has an effect on the flavor you get - strong but under-extracted coffee tends to be very bold but nutty and lacks both bitterness and some nuance.

                      If you're trying to get even stronger coffee from an Aeropress, how you should go about it depends on exactly what effect you're going for. Happily, the Aeropress is capable of quite a bit of variation in the effects it can manage. If you want more bitterness and complexity, you might go for a higher extraction. This can be accomplished in a few ways. The easiest is just to brew with hotter water than the directions call for. Preheating the system can also help. Stirring more vigorously or grinding more finely (to a point) or brewing for a longer time can have a similar effect, and if you brew at or near the lower temperatures the Aeropress recommends, you can get a little more complexity without much bitterness by messing around with these variables.

                      Beyond that, you'll tend to get a higher extraction by using a lower ratio of coffee to water, all other things being equal (inverted brewing can help here). But if you do this, you'll need to mess with other variables to achieve the same strength. Likewise, increasing the coffee to water ratio will tend to lead to a stronger brew, but you'll have to mess with other variables to get the same extraction.

                      If you're pulling concentrated shots from the aeropress, how packed the coffee is doesn't make quite as much of a difference as you might expect - the coffee to water ratio is so high that you won't have a whole lot dripping through the filter prematurely either way. But if you're brewing non-inverted with lower ratio of coffee to water, then pre-dampening the coffee or packing it tightly can make more of a difference. Inverted, the packing doesn't have a huge effect either.

                      The pressure you use on the plunger probably does have some effect on the final brew strength, but it can be harder to predict than messing with other variables. I'd suggest that you stick with a plunge that takes 20-30 seconds and try to work with other variables if you want different results.

                      In the end, it all depends on exactly what effect you're going for. If you find your results aren't quite what you wanted and can describe the difference in effect, I might be able to brainstorm a method or two to try to get results more to your liking.

                      1. re: cowboyardee

                        Thanks, that helps a lot actually. You can see my brew method in my reply to Panini Guy below.

                        I like my coffee strong because it is immediately iced.

                        My "final" question is what's the difference between using more water while extracting (ie what I do below, which is 2x30s grinds and filling up the aeropress to the top with water, using the "4" setting with an inverted brew), vs the method the aeropress recommends (which would be using significantly less water while extracting due to using the "2" or "3" setting, and then adding water?

                        When using the aeropress method, the amount of coffee i actually get from the press seems sooo small.

                        1. re: ns1

                          Basically as follows:

                          More coffee bean, less water = lower extraction, higher strength

                          More water, less coffee bean = higher extraction, lower strength

                          Stirring more, using hotter water, using a finer grind, increasing brewing time, insulating the aeropress, preheating the aeropress = higher extraction AND higher strength

                          The directions the aeropress call for a high ratio of coffee to water, somewhat low temperature, short extraction time - all of which leads to stronger but underextracted coffee. Nutty, flavorful, lacking bitterness and some top notes and subtlety. Your method leads to coffee that is probably weaker but more extracted. Not quite as strongly flavored but more complex. You could get stronger coffee out of your method by using more coffee grounds without otherwise changing your method - that's where I'd start my experiments if I were you and looking to get a stronger brew. Then I'd fine tune.

                          1. re: cowboyardee

                            thanks, appreciate it. I actually decreased my coffee/water ratio because I didn't notice a difference - I used to run 2x45s grinds using the same method.

                            I'll give it another whirl drinking it straight black to see if my coffee tastebuds have matured at all.

                            One note...

                            "More coffee bean, less water = lower extraction, higher strength"

                            The aeropress calls for adding water AFTER pressing, wouldn't this dilute the finished product? Thus making the aeropress method lower extraction + lower strength? (IIRC they call this an "american style coffee")

                            1. re: ns1

                              "The aeropress calls for adding water AFTER pressing, wouldn't this dilute the finished product? Thus making the aeropress method lower extraction + lower strength? (IIRC they call this an "american style coffee")"
                              It does dilute the finished product - obviously, the concentrate is a lot stronger before water is added to it. Technically speaking, this doesn't change the extraction % - you've gotten the same amount from the beans whether or not water is added to the solution afterward. But the extraction was low in the first place.

                              Thing is, the directions for the call for so much coffee that the result of a fully diluted aeropress 'Americano' winds up being normal to a bit strong compared to other brewing methods, but is also under-extracted.

                  2. re: ns1

                    There's no simple way to answer that. It depends on which variables you maintain consistently brew to brew. Let's say you have an ounce of coffee (~28g) to brew in a press pot. If you put in 16oz of 200F H2O and press after 4 minutes, you're going to end up with a cup that's pretty close to an ideal extraction for that coffee. But you could also add 15oz water and pour out the brewed coffee without pressing to lessen extraction. Or you could add 17oz of water and agitate throughout the process to increase extraction before pressing. Those three cups won't be identical, but probably pretty close in taste and body.

                    Dose, grind size, contact time, amount of water, water temperature, pressure... all have bearing on the final cup.

                    I don't have experience with the phin to really understand the process. But, if you're familiar with the concept of a 'ristetto' shot of espresso (concentrated short pull), there are several ways to 'fake' that output. Traditionally (Italian) the ristretto is a 7 gram single shot where the water flow is cut short so that the coffee bed underextracts (significant coffee flavor components left in the puck) leading to less volume in the cup but a more concentrated intensity.

                    You could also reach a "ristretto-style" shot by overdosing a portafilter with the same grind size and a standard amount of water, or fining the grind (Turkish grind) with a standard amount of water.

                    The screw-down phin isn't like any other brew method I'm aware of. Since everything I've read on it maintains a medium-coarse grind should be used along with a specific amount of water per coffee dose (~14:1 ratio), the result will always be underextracted. However, I have to think that something about the inability for the coffee to expand is also at play in the quality of extraction, along with the use of robusta coffee (or in the case of Cafe DuMonde, robusta plus chicory).

                    There is a lot of information on extraction here: although they don't discuss phin brewing. Still, the scientific concepts would apply to any brew method.

                    1. re: Panini Guy

                      Thanks, very interesting. I don't follow the instructions that were originally given to me by the aeropress at all...

                      2x30s grinds on the grinder @ finest setting. I leave the Aeropress on the "4" setting, put all the grinds in, and fill with water to the top using the inverse brew method. I agitate for the first 30-60 seconds to make sure the water is doing it's thing (I imagine this is exactly like a chemex up to this point). Then I let it sit there...for 4-15 minutes. Then press out.

                      Sooooo what am I doing to my coffee? Most items are perfectly consistent day in and day out (always 2x30s grinds, water at same temp, aeropress on same settings). The only variable is how long I let the coffee sit before I press - sometimes it's 5 minutes sometimes it's 15...

                      Anyway I'll check out the coffeeresearch site; I've been less than enamored with coffeegeek.

                      1. re: ns1

                        One of the weaknesses of the aeropress is that it loses temperature quickly. Longer extractions hit the point of diminishing returns comparatively quickly. That said, you can fudge the aeropress to get even more dramatic results from a longer brewing time by preheating the system thoroughly and insulating the outside of the brewer with foam - a large cut up styrofoam cup will do the trick.