In the early 1800’s, European vintners were seeking a reliable way to determine the perfect time to harvest wine grapes, an important objective when a high quality bottle sold for hundreds more. Several methods were pioneered, but the one that most interests us most is the measure of total dissolved solids: the amount of stuff in the grape juice. With this understanding European vintners were better able to manage plant health and produce consistently higher quality grapes. This technique can easily be applied at home with a nifty little gadget called a refractometer.
The refractometer measures in degrees Brix (°Bx). The scale is based upon the quantity of dissolved cane sugar in water and equates to percentage. Thus a reading of 1° Brix is 1% dissolved sugar and 99% water, and 25° Brix is 25% dissolved sugar and 75% water. The tool is calibrated to 0° using distilled water.
The refractometer works like a prism. When light is passed through different substances it bends and reacts slightly differently from one another. To take a measurement, a small drop of liquid is placed on the refractometer window and pointed at the light. The degree of light bend is then displayed on a scale you can read through the eyepiece.
Since a large part of plant juices are made up of sugars and water, this is an excellent way for us to obtain a usable and very accurate reading. For example, grape must is mostly glucose, not sucrose, but the Brix is still within 0.1 degrees, a level of accuracy more than sufficient for our use. Like grape must, all plant juices contain a whole lot more than simple sugar (minerals, proteins, fats, vitamins, amino acids, etc), so when the tool is used in this way it is referred to as “total dissolved solids” or “total soluable solids”.
In addition to 200 years of use among grape growers, the refractometer is well known within the food industry for things like fruit juice, jams and jellies, soft drinks, beer and numerous scientific and industrial applications.
There are numerous types of refractometers on the market, but we just need one: a hand held refractometer with a scale from 0-32 degrees. The only garden vegetable you will encounter that exceeds 32° are garlic cloves. The brix reading is also somewhat temperature sensitive, so getting a device with ATR (Automatic Temperature Regulator) will save you from doing some extra math.
This is what I recommend:
- Refractometer, 0-32 degrees, with ATR
- small pocket notebook and pencil
- garlic press
Brix testing is one of the easiest and most informative tools available for gardening. You can use it to monitor your plant health, including the health of your weeds, and it allows you to grade the quality of fruits and vegetables at harvest.
I record all my readings into a notebook sorted by plant type: apples, oranges, carrots, broccoli, etc. To take a measurement carefully squeeze a drop or two of liquid from your plant leaf, fruit or vegetable. If the plant part is refusing to give you a good drop, use the garlic press. Place the drops onto the prism and look through the eyepiece and record the reading. You now have a point of reference you can use to measure your success with.
You can actually use your refractometer to measure any liquid, and I’ve had a lot of fun with mine. I test milk, tap water, bottled water, coffee, tea and all the soda’s at work. I also test every fruit and vegetable I can get my hands on: the store, the farmers market, backyards; and I always record whether it was organic or not.
The refractometer has proved itself in giving results in the field for 200 years of viticulture, and is an accepted tool in biological agriculture. It’s a great tool, but it’s not the only tool, and it does take some knowledge to use effectively, but more detail on that later. You can get a refractometer quite inexpensively, I bought mine (Vee Gee BTX-1) off of Amazon.