Measuring Brix With A Refractometer

The importance of this test is to avoid problems with bugs, disease, and to assure that you are growing food that will benefit your health.  Below are a couple charts that show the relative Brix that can be expected.

... Low-Brix plants can’t develop the strong extraction fluids to pull minerals from the soil. As a plant matures, it requires more and more soil energy to extract nutrients from the soil. Reams continually stressed the fact that while a baby seedling had minimal daily nutrient needs from the soil, a mature plant drawing down heavily was an entirely different story. He taught that for a plant to bear a full crop of high quality produce it must have adequate soil energy (called "ERGS" or Energy Released per Gram per Second) available to "set" the high-quality crop and then "bring it home." ERGS is merely a measurement of the ionic conductivity of the soil expressed as microSiemens and directly measured with an ordinary conductivity meter. The point is that only healthy soils with teeming bacterial life and full mineral availability can "keep up" when the plant roots are most demanding. - Nutrient Dense Food High Brix Farming-Gardening

“In essence, I discovered that there was a direct correlation between the hydrogen content in the cell and plant health. At the ideal of 6.4, the hydrogen content of plant fluids is approximately
12%.”...“I don’t care what crop you check, 6.4 is the key factor. If it’s not there, you have an imbalance and potential problems. You can tell what the im balance is by backing up with brix levels.”  - GSait Plant Health Energy Managment PDF




Ideal sap pH-level for optimal plant growth and production is pH 6.4
If sap pH exceeds 6.4, this probably means a shortage of the anions nitrogen, phosphate or sulfur. At pH 8 the odds of insect trouble is 100%.
Conversely, if sap pH is lower than 6.4, then there is a cation problem, with possible deficiencies of calcium, magnesium, potassium and/or sodium. Low sap pH suggests a far greater potential for foliar disease. At pH 4.5 the probability for fungal appearance is 100%. - Principals to Produce Nutrient Dense Crops PDF  -Bruce Tainio

 

Temperature, 68 °F (20 °C)
Specific Gravity	Brix		Specific Gravity	Brix		Specific Gravity	Brix
0.990	0		1.038	9.5		1.085	20.43
0.991	0		1.039	9.74		1.086	20.65
0.992	0		1.040	9.98		1.087	20.88
0.993	0		1.041	10.22		1.088	21.1
0.994	0		1.042	10.46		1.089	21.32
0.995	0		1.043	10.7		1.090	21.54
0.996	0		1.044	10.94		1.091	21.77
0.997	0		1.045	11.18		1.092	21.99
0.998	0		1.046	11.42		1.093	22.21
0.999	0		1.047	11.66		1.094	22.43
1.000	0		1.048	11.9		1.095	22.65
1.001	0.26		1.049	12.14		1.096	22.87
1.002	0.51		1.050	12.37		1.097	23.09
1.003	0.77		1.051	12.61		1.098	23.31
1.004	1.03		1.052	12.85		1.099	23.53
1.005	1.28		1.053	13.08		1.100	23.75
1.006	1.54		1.054	13.32		1.101	23.96
1.007	1.8		1.055	13.55		1.102	24.18
1.008	2.05		1.056	13.79		1.103	24.4
1.009	2.31		1.057	14.02		1.104	24.62
1.010	2.56		1.058	14.26		1.105	24.83
1.011	2.81		1.059	14.49		1.106	25.05
1.012	3.07		1.060	14.72		1.107	25.27
1.013	3.32		1.061	14.96		1.108	25.48
1.014	3.57		1.062	15.19		1.109	25.7
1.015	3.82		1.063	15.42		1.110	25.91
1.016	4.08		1.064	15.65		1.111	26.13
1.017	4.33		1.065	15.88		1.112	26.34
1.018	4.58		1.066	16.11		1.113	26.56
1.019	4.83		1.067	16.34		1.114	26.77
1.020	5.08		1.068	16.57		1.115	26.98
1.021	5.33		1.069	16.8		1.116	27.2
1.022	5.57		1.070	17.03		1.117	27.41
1.023	5.82		1.071	17.26		1.118	27.62
1.024	6.07		1.072	17.49		1.119	27.83
1.025	6.32		1.073	17.72		1.120	28.05
1.026	6.57		1.074	17.95		1.121	28.26
1.027	6.81		1.075	18.18		1.122	28.47
1.028	7.06		1.076	18.4		1.123	28.68
1.029	7.3		1.077	18.63		1.124	28.89
1.030	7.55		1.078	18.86		1.125	29.1
1.031	7.8		1.079	19.08		1.126	29.31
1.032	8.04		1.080	19.31		1.127	29.52
1.033	8.28		1.081	19.53		1.128	29.73
1.034	8.53		1.082	19.76		1.129	29.94
1.035	8.77		1.083	19.98		1.130	30.15
1.036	9.01		1.084	20.21
1.037	9.26

On July 12th Justin and I tested some tomatoes.  The cherry tomatoes are probably all the same variety but the beefsteak tomatoes are different varieties.   I know that's not real scientific, but it's how my garden was planted.  The hugelkulture bed is has not had time to mature so basically it is 8" of compost over dirt and wood.

Variety	Method	Specific Grravity	Brix
Beefsteak tomato	Hydroponic	1.044	10.94
Cherry tomato	Bioponics	1.044	10.94
Beefsteak tomato	Hugelkulture	1.030	7.55
Cherry tomato	Hugelkulture	1.041	10.22
Beefsteak tomato	Wicking Bed	1.026	6.57
Cherry tomato	Wicking Bed	1.043	10.7
Medium tomato	Wicking Bed	1.022	5.57
Round Roma tomato	Justin's dirt garden	1.035	8.77
Yellow pear tomato	Justin's dirt garden	1.058	14.26
Brandy Wine tomato	Justin's dirt garden	1.040	9.98
Mortgage Lifter	Justin's dirt garden	1.038	9.5
Long Roma tomato	Justin's dirt garden	1.030	7.55
Cucumber	Justin's dirt garden	1.035	8.77
Yard Bean	Justin's dirt garden	1.035	8.77

Justin and I discussed the differences in our gardens. The Brix levels of our vegetables are not that much different.   But I would say his garden is producing more vegetables than mine, and he estimates this year's garden is about 4 times as productive as last years garden.  It truly is a great garden.  
It's anecdotal but we came to a conclusion that it is probably the amount of Azomite we each added.  Justin was far more generous with the micro-nutrients.  Justin has also added some organic fertilizers whereas I have only sprayed with compost tea.
But the bottom line is we both have above average brix, and no pests which I attribute to an abundance of micro-nutrients..  My soil is 80% compost and 20% worm casting.  Justin's soil is a fine loam which has seen many years of gardening and received a healthy dose of Azomite.
My hydroponic garden is extremely healthy and productive, but it's not organic and uses petroleum based fertilizer. 
I may buy some pH test paper and update the post with the sap pH levels in my test gardens.

I've made a spreadsheet for converting specific gravity to brix available on DropBox.com
https://dl.dropboxusercontent.com/u/20676945/SPG_Birx%20Chart.ods

 Or you can go to 

http://www.brewersfriend.com/brix-converter/