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Brix Testing  RSS feed

 
Su Ba
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I found this on the www.ag-usa.net website. It may be of interest to plant growers.

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Brix Readings, and What They Tell Us


Brix – A unit of measure used in the refractometer. When the Brix reading is divided by 2 it will be equal to the percent of crude sucrose in the plant tissue.

Refractometer – A device used to measure the refractive index of plant juices in order to determine the mineral/sugar ratio of the plant cell protoplasm.

Refractive Index of Crop juices are calibrated in percent sucrose or degree Brix.

During the growing season it is possible to check a plant for percent sucrose. A refractometer is easy to use. You will need something like a garlic squeezer for juicing the plant sample. To make a reading, place 2 to 3 drops of the liquid sample on the prism surface, close the cover and point toward any light source. Focus the eyepiece by turning the ring to the right or left. Locate the point on the graduated scale where the light and dark field meet. Read the percent sucrose (solid content on the scale).

The refractometer measures in units called Brix. The Brix equals to percent crude carbohydrate per 100 pounds of juice. The higher the carbohydrate in the plant juice the higher the mineral content of the plant, the oil content of the plant, and the protein quality of the plant.

For example, if you were to have 100 pounds of alfalfa that has a Brix reading of 15 it would mean that there would be 15 pounds of crude carbohydrates if the alfalfa was juiced and dried to 0 percent moisture. By dividing 15 by 2 it tells us that the actual amount of simple sugar would be equal to 7.5 pounds.

Crops with higher refractive index will have a higher sugar content, higher protein content, higher mineral content and a greater specific gravity or density. This adds up to a sweeter tasting, more mineral nutritious feed with lower nitrates and water content and better storage attributes.

Crops with higher Brix will produce more alcohol from fermented sugars and be more resistant to insects, thus resulting in decreased insecticide usage. For insect resistance, maintain a Brix of 12 or higher in the juice of the leaves of most plants. Crops with a higher solids content will have a lower freezing point and therefore be less prone to frost damage.

Brix readings can also indicate soil fertility needs. If soil nutrients are in the best balance and are made available (by microbes) upon demand by plants, readings will be higher.

You will find that when the phosphate levels in the soil are not up to what they should be, the sugar in the plants will vary from the bottom of the plant to the top. In other words, the Brix reading at the bottom of the plant will be higher than the top of the plant. The better the phosphate levels in ratio to potassium the more even the Brix reading will be all over the plant. Also the better the phosphate levels in ratio to potassium the less fluctuation there will be in the brix reading in any given 24 hour period.

You will also note that when you are looking into a refractometer you will sometimes be able to see a very sharp line which is very easy to read, while at other times it may be a very hazy line and not well demarcated and so difficult to read. The very sharp and dark and easy to read line means the crop is lower in calcium and higher in acid. A very diffuse and hard to read line tells one that the calcium is higher and the acid is lower in the plant. This is why a lower Brix reading on a plant will actually taste sweeter when there is high calcium than one that may have a little higher Brix reading and a low calcium. The available soluble sugar is what gives taste and sweetness to food. The more calcium in the crop along with the sugar, the sweeter the taste even though the Brix reading will be the same on two samples.

Source: Frontier Labs, Inc; Biologic Ionization as Applied to Farming and Soil Management, Beddoe.
 
Joseph Lofthouse
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For me, fuzzy readings on a refractometer are typically due to using cloudy juices instead of clear juices.

For me, the sweetness of fruits typically has little to do with brix, and has a lot to do with how many bitters are in the fruit. The sensation of sweetness then depends on whether there is enough sugar to overpower the bitter components. That's why I am growing yellow watermelons. Because the red color in melons tastes bitter, but the yellow color doesn't. So a yellow watermelon with lower brix tastes sweeter than a red melon with high brix.

 
Su Ba
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Location: Big Island, Hawaii (2300' elevation, 60" avg. annual rainfall, temp range 55-80 degrees F)
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Interesting observation, Joseph. I always found red watermelon to be bland. Yellow ones were sweet. I think I'll test the brix on the watermelons this summer.....if I can remember. I had better write myself a note. 😊
 
John Polk
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The sensation of sweetness then depends on whether there is enough sugar to overpower the bitter components.

Case in point: I often buy a bottle of cherry juice, or the sour cherry juice.The last time, I got 1 of each. Reading the nutrition labels, I was surprised that the 'sour cherry' actually had more sugars in it. (And neither of them had any added ingredients - just cherry juice.)
 
John Polk
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If you would like to see some base Brix numbers for various fruits/vegetables, download this BRIX CHART

It will give you some guidelines to see how your produce fits on the scale.
 
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