The principle and method of measuring coffee concentration refractometer what is the appropriate coffee concentration?

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There are many ways to measure the concentration of coffee extraction, from the troublesome drying method, to the inaccurate conductivity meter or hydrometer, then to the conversion of sugar meter, and finally to VST's refractometer digital refractometer; from then on, it is generally recognized that this is the fastest and most accurate measuring equipment. Even after a few years, the PAL-COFFEE refractometer launched by ATAGO in Japan is designed according to the same concept.

The concentration is used to convert the extraction rate of coffee. In general, the soluble matter of coffee beans accounts for 30%, and the other 70% is insoluble fiber. According to the survey conducted by Earnest Lockhart in the 1960s, for Americans, the coffee extraction rate of 1.15 to 1.35% and 185.22% (179.21% in the words of VST founder Vince Fedele) would be the best flavor range, while the European preference concentration would be higher. Get the extraction rate, you can establish a set of coffee brewing standards, in addition to qualitative adjectives, but also have quantitative data for reference.

The hardware of the VST refractometer is designed and manufactured by MISCO and sold with self-developed software. The basic structure is as shown below, through the light source, prism, photosensors, using the change of the concentration of the liquid on the prism, resulting in the difference of refraction angle, to convert its concentration.

The wavelength of light also affects the angle of refraction, which is the principle of dispersion. For example, the picture of the album The dark side of the moon shows that when light passes through different media, the refraction angle of red light is the smallest and that of purple light is the largest. If the refractometer uses such a combined light source, the data read will have a great error; at present, it is known that sodium light is the simplest, and its wavelength composition is only two: 589.0 nm and 589.6 nm, which is very close, so it can be regarded as a monochromatic light source, so the influence of dispersion will be reduced to a minimum, and the data will be accurate and reliable. This is why there is a yellow light when measuring concentrations, regardless of VST or ATAGO.

I have been using this refractometer for several years. Recently, I reread the instruction manual. The main points are as follows:

1. There is at least 0.03% measurement accuracy in the range of 15 degrees Celsius to 30 degrees Celsius.

two。 It needs to be corrected when the room temperature change is more than 1 degree (in theory, but it's really troublesome, and it doesn't seem to make much difference)

3. The sample temperature should be consistent with the prism temperature.

4. If the wavelength of the light source is different, the TDS value read will be different. The wavelength is inversely proportional to TDS. (VST/ATAGO has used yellow light, don't worry.)

5. Measurement steps: coffee mixing evenly-> sampling-> waiting for 60 seconds to cool-> dripping coffee on the mirror-> waiting for 30 seconds to make the temperature consistent-> reading value

The point is that the temperature of the coffee sample and the prism must be the same, otherwise it will also affect the accuracy of the data; the initial use is often ignored because of impatience. I have both the VST II and the PAL-COFFEE, but if PAL-COFFEE buys the BRIX version, it must be converted by 0.7947 to TDS. After the measurement and comparison in the morning, there still seems to be some error.

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Coffee beans: Emerald Manor sapphire 15g, little Fuji ghost tooth scale 2.5

Water: 250g, injection temperature 89 degrees

Use smart filter glass version: steam for 30 seconds, soak for 3 minutes

VST TDS: 1.25%

ATAGO Brix: 1.60%

There is a foreign comparative report A Refractometer Comparison, which mentioned that the concentration value of VST II is higher, but VST III and ATAGO have the same result, so it may be more accurate to deduct some values when using VST II.

In addition, the above sugar meter or coffee concentration meter measures the refractive index of the solution, not the true sweetness or concentration. Occasionally see people on the Internet will misunderstand, there is no need to explain at this time, ask the other side to soak a cup of salt water to measure, you can also get a very high value, it can be proved that this is not sweet at all.

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