treston Senior Member Joined: 15 Aug 2006 Posts: 10 Location: Ireland Expertise: Just starting
Posted Mon Jan 7, 2008, 8:59am Subject: Re: Measuring Coffee Strength With A Brix Meter
Another person I showed it to was Randy Pope of the Bunn Technology Center. Randy pulled out his own Brix meter and told me that he’d been using it for eleven years and that it was very accurate. He also shared measurements he’d made to correlate Brix to Total Dissolved Solids as measured with his dehydration instrument. He found that 0.85 x Brix equals the percent Total Dissolved Solids (TDS).
I have done tests on 14 different brews, 7 different brew settings using 2 coffees. I use the SCAA TDS meter and a digital brix meter. I found my own derived number to be 0.83 for one coffee and 0.84 for a second. I also did hydrometer testing, not the SCAA hydrometer whose scale is for coffee, I used a Widder hydrometer in the scale 1.0000-1.0070, they showed the same sort of variations. I have yet to plot them altogether, I was looking for a conversion formula for SG to TDS before, and will get my own figure from these readings. I trust the hydrometer readings most as they are truely dependent on dissolved solids.
If anybody has any conversion factor/formula for SG to TDS please let me know.
The dehydration method is going to have some undissolved solids in it. I am not sure how much undissolved solids will pass through, depends on the filter paper and probably other factors too. I would imagine the brix meter will be unaffected by undissolved solids. I think the electrical conductivity meter (the TDS meter) would be affected by solids, since current will pass through a soaked solid, and I have found variance in testing coffee which has been allowed to rest for weeks, and then stirring it up.
Since many are working to coffee brewing control charts it would be best to use what they originally did. Were they developed around dehyration methods? Is the strength based on hot coffee (which has a lower TDS than cooled coffee due to volume differences). Or were the graphs calculated in another way altogether?
Randy arrived at the figure of 0.85 using dehydration. When I compared against a TDS meter I got 0.83. This would make sense to me since the dehydration method should have some undissolved solids, and therefore when dried it will weigh more than just the dried dissolved solids. But the difference is very small and could have gone the other way too!
These are small discrepancies but factors of error can add up. The coffee should ideally be central in the box anyway, but I would still like to be as exact as possible.
When I make coffee in my Newco OCS-8 I use 48 oz of input water and 2.0 oz of coffee,
This equates to 39.9grams per Litre, where the outer lines on the SCAA "ideal box" are 63.65 and 48.67 grams per litre. Therefore it is never going to be able to be within the "ideal box". As you mention, use more coffee, going to 3oz, which is ~60g/L. Grind, brew times & temperature can be adjusted too. Some places will work with individual portion sized packets, therefore changing the water quantity can be a better option, rather than messing with half packs.
Posted Wed Jun 4, 2008, 11:23am Subject: Re: Measuring Coffee Strength With A Brix Meter
Now days I always dose near 16 to 1 or 6%. I find it easy to get 1.5 brix when using the pour over method for 16 or 32 oz but the auto drip brewers like the NewCo-8 seem to over extract and I have to use less coffee.
edit: I don't use auto's anymore but if I did I guess I would use 3 oz in the NewCo and just grind courser until I got 1.5 brix.
treston Senior Member Joined: 15 Aug 2006 Posts: 10 Location: Ireland Expertise: Just starting
Posted Thu Jun 5, 2008, 2:19am Subject: Re: Measuring Coffee Strength With A Brix Meter
A lot of commercial roasters supplying packets may have adjusted the roast & grind to try and overextract the coffee on purpose. It is trying to squeeze the last bit out of the bean in an attempt to make more money, even though the cost of the coffee bean is a tiny fraction of the cost charged to the customer.
I am not sure what is needed to pass the SCAA "gold cup". The European Coffee Brewing Centre (ECBC) based in Norway have a similar ideal cup range on a chart, but it is 1.3-1.55% TDS and the same 18-22% extraction. This range is higher than the SCAA range to suit the local taste for stronger coffee, the SCAE have a different range again, 1.2-1.45% TDS and 18-22% extraction.
To pass the ECBC test is not just a simple case of getting in the ideal range on the chart. Brew time, grind, temperature, wetting, basket size & depth of coffee bed in basket all have to be within certain ranges. Many machines at factory settings could never pass the ECBC test, many will have longer brew times which are used to overextract the low weight of coffee used, just to up its strength at the expense of quality.
I am not sure if the SCAA has any other criteria like this before a cup is certified, or if it is simply a case of getting in the ideal box.
At the risk of reviving an old thread... There might be some interest in talking about refractometer readings (in Brix) and other measurements in coffee.
I've been using an analog Brix refractometer for a few months. Got it for about 35CAD (about 32USD) from a group order among beer homebrewers. We use these to measure the quantity of sugar in beer wort which, itself, is used to determine the alcohol content of the finished beer. Having read this thread when it first came out, I thought I'd use it with coffee. Which I've been doing ever since I got the meter (February 13). In fact, I've been posting data points on Twitter and other microblogging systems. It's a way to take notes in public. Got some people intrigued. I don't do espresso at home and I haven't made measurements in cafés. The three main devices I use at home are a six-cup Bialetti Moka Express, a generic six-cup moka pot, a two-cup Bialetti Brikka, and an Aerobie AeroPress. Altogether, I have 153 measurements in five months (42 AeroPress, 17 Brikka, 3 moka pot, 91 Moka Express). For every coffee I make, I weigh grounds and water (using a small digital scale), take the coffee temperature (using a digital probe thermometer), measure the Brix. and write down some tasting notes. With moka pots, I also time the brew and I occasionally mist the grounds (2-6 ml). With the AeroPress, I also take the quantity and temperature of the coffee after the brew. Just compiled the results. Haven't really looked at the data in detail. But a few general notes...
Just taking those readings has an impact on my coffee brewing. I pay more attention to the different variables and end up noticing some patterns. Nothing extremely specific, maybe, but my senses are more finely tuned to coffee tasting.
The Brix value is pretty much what one would associate with "brew strength."
The value itself may not be that important as it doesn't necessarily correlate with how good the coffee is.
I'm not extremely clear about the precision but I think it's quite robust as a measurement method.
Some local café owners (at Myriade) have been experimenting with a coffee-specific refractometer and seem happy with the results. More so than with TDS.
In terms of getting the sample to temperature, I usually just leave a few milliliters of coffee in a saucer and I take the reading later on. The darkness of the liquid is often a fairly good (but imprecise) predictor of the approximate Brix reading.
I personally don't think so much about body. But I do notice differences in flavour clarity.
My Brikka can get in espresso territory in terms of Brix (3.0°Bx-5.9°Bx, average of 4.2°Bx, 0.9 std dev).
My Moka Express tends to get around 2°Bx (1.0°Bx-4.1°Bx, average of 2.1°Bx, 0.6 standard dev).
The AeroPress can give a broad variety of results , in terms of both flavour profile and Brix reading (1.6°Bx to 4.2°Bx, average of 2.5°Bx, 0.6 std dev). In fact, that's something I like about the brewing device: it helps me get flavour diversity, even with the same beans. Getting the same flavour profile every time is really not something I find enviable, especially at home. If I wanted consistency in flavour, I'd drink instant coffee.
I tend to add more variables as time goes by. With the AeroPress, for instance, I got started taking the temperature of both the water itself and the mix of water and grounds. There seems to be a decrease of about 6°C, in a matter of seconds.
As for the constant (Brix * K = grounds / brew), I'm not really getting one. With my Moka Express, I get 13.2 to 31.8, average 22.0, standard deviation of 4.1. With the AeroPress, I get 12.8 to 25.9, average of 18.9, standard deviation of 3.9. With Brikka I get 12.0 to 23.7, average of 18.5, standard deviation of 3.2. I probably need a lot more data, but the ranges seem wide enough to necessitate some explanation and make it difficult any comparison between brewing methods. I tried to find a similar constant with the "grounds to water ratio," but I don't seem to get tighter data: AeroPress 15.0 to 30.0, average 22.6, std dev of 3.4 Brikka 16.0 to 31.1, average of 24.0, std dev of 4.4 Moka Express 15.4 to 40.0, average 25.0 std dev of 4.7
Maybe my refractometer just isn't precise enough or something else is inconsistent in my method.
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