I've read some sites that talk about Brix levels in vegetables, and how we should aim to reach high levels in the edibles we grow.

What is brix, and is it something we can inexpensively measure at home? And if it's good, how do we increase levels?

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    Brix is a measurement of sugars in an aqueous solution, so unless you're intending to liquify your vegetables, there's no way of measuring it I'd also consider it largely irrelevant in ordinary vegetables,, one would more likely want higher levels of minerals and vitamins rather than increased sugars.
    – Bamboo
    Jan 9 '17 at 10:37
  • @bamboo: tomatoes are easy to "liquefy". But I saw how easy it is to mash/blend carrots in order to have a juice, so I'd expect it is possible for some other vegetables. Measuring vitamines is very expensive, and it will give the "wrong" information. Nobody working on wholesale will accept a method which show that they product are bad. (harvest still not fully ripe/mature, so with low vitamins levels, lower than published everywhere, and used for daily dosis). Jan 9 '17 at 14:02
  • @GiacomoCatenazzi - just been researching, and discovered a reason other than just for sugar levels why Brix might be significant, but not sure its worth bothering with for home growers or amateurs, but might be for large, professional growers. Will try to add an answer tonight some time, but am short of time at the moment... you got my vote already anyway!
    – Bamboo
    Jan 9 '17 at 18:36
  • Some people say that increasing the soil life increases the brix. I have a friend/acquaintance with a refractometer who believes this (and I know he's not the only one). I think what causes brix to rise might depend on the variety of your chosen species, however (I think it's like trying to figure out what makes tomatoes mealy). I mean, a lot of tomatoes have more flavor/sugar in sunny conditions, but they're not all tasteless in lower temperatures/light. Anyway, soil temperature could certainly change the microbes present, though. Nov 25 '17 at 7:21

Brix is a measurement of sugar in liquid foods.

I check Brix degree to sell my grapes. They pay me pro Brix/Kilo (with some maximal limit of Brix, and maximal Kilo per square meter). For wine I understand that sugar is direct proportional with alcoolic degree in wine, and people now think that a strong wine is better then a "soft" wine.

I know that Brix is used also for beer, and for honey.

For vegetable I don't know. It is an objective measurement of how mature are tomatoes etc., so it can be a good specification for contracts, but I don't think it is the best way to have better vegetables.

For own consumption I think it is not a good way to select better vegetables (nor the size of the vegetables). One should really taste vegetable and find what it is the best taste/maturity for a specific use. I usually don't like overmature vegetables.

How to measure?

Usually there is two instruments: densimeter and refractrometer. Both measure the density of pulp "liquid". The first one is cheap (less than 10 dollars): it is a scale which sink in the liquid. The refractrometer costs more (10 times more), and uses optical refraction index. This requires a lot less liquid (few drops) and quicker to do many measures. I think it is the only one which work for honey (very dense matter).

  • 1
    In the USA, the homebrewing hobby has somewhat lowered the relative price of refractometers. Checking a drop of juice is somewhat common in evaluating the progress of a commercial fruit orchard (plums, cherries, apples, etc.) as well as grapes - it's would be far more difficult to check those with the densimeter/hydrometer apparatus, as a much larger sample is required. I guess once you had one you might evaluate other things, but most of us at home will simply eat a fruit and decide that it's not ripe yet, or it is - the quantitative measurement is not required in a home garden setting.
    – Ecnerwal
    Jan 9 '17 at 13:36
  • I'm asking about brix levels in vegetables. The answer I'm looking for has to do with nutrients, and liquid carbon flow. Jan 9 '17 at 18:42
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    @GrahamChiu: brix is about sugar, not really nutrients. If that is the question, it is too wide, you should restrict. Every vegetable and variety has different sugar level at maturity. And this depends also on region of growth. Jan 9 '17 at 19:43
  • I know a gardener who says life (microbes) in the soil increases the brix of fruits/vegetables. He has a refractometor, and a product he makes that he says increases the soil life. I could tell you what's in it, but I don't know that he would like that. Jan 10 '17 at 6:41
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    @Shule: An healthy plant increases the sugar level, so the brix grades. Sun is the most important factor, but soil is also important. But 1- sometime we don't want too much sugar or healty plant (stressed plant usually produce more "flavour", e.g. in chilli plant, or in fruity wines, or in aromatic herbs), 2- sometime healthy plany will produce much more fruits (e.g. tomatoes) or leaves, which could decrease the sugar level per fruit/leave. (So also cultural measures should be taken into account, to increase brix). Jan 10 '17 at 7:38

Brix is the measure used by a refractometer when measuring the amount of dissolved solids in a solution. You can extract the sap for testing from the plant by using a garlic crusher on leaves, stems, and fruit.

The refractometer measures the degree to which light is refracted by the solution and is usually temperature corrected to 20 deg C (ATC). If you divide the result by 2, you get a crude measure of the amount of sucrose in the plant tissue. You can purchase a refractometer for about USD25. The test should be done on a sunny day in the afternoon using sunlight. Brix levels vary during the day and also at different levels of the same plant.

Plants are autotrophs which means that they make their own food. Animals are heterotrophs as they either eat plants, or eat animals that in turn eat plants. And interestingly, over 95% of the bulk of a plant comes from carbon dioxide extracted from air. The remainder of nutrients and minerals are drawn from the soil. You can see for yourself that when trees grow, the ground mass around the roots does not shrink as it is taken from the ground since most of tree mass actually comes from the air.

So, plants make their own food by photosynthesis which produces carbohydrates. These sugars are used for cellular respiration, and any left over are used for building plant tissue and other processes as discussed below. So, high levels of soluble carbohydrates tells us that the plant is more likely meeting its genetic potential:

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.

Healthy plants are in a position to create plant chemical defences being their secondary metabolites which are phenolic compounds: terpenoids, sesquiterpenes, bioflavenoids which increase nutrient density.

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.

High Brix levels also mean that more carbohydrates, and amino acids will be available to be exuded by the roots to feed the soil bacteria which can then make minerals more readily available for the roots (mineralisation).

Some 25% of the total sugars produced in a healthy plant are released as root exudates, and this occurs mainly at the framing stage of the plant when 70-80% of sugar production is diverted to the soil for bacterial growth. The bacteria are in turn consumed by protozoa, nematodes and microarthropods releasing their nitrogen, amino acids and other metabolites to the soil. When the plant is fruiting, it is then able to draw on these mineral reserves built up in the soil. These minerals are now available in plant bioavailable form, and furthermore, as prefabricated components such as the amino acids. With the increased growth spurt, the plant starts to send lipids to the roots and as root exudates that can be used by the soil fungi to eventually create stable humic substances in the rhizosphere.

Hydroponic growers can also monitor Brix levels to pick up early problems.

Taking a brix measurement is standard operating procedure for hydroponic crop advisors in Europe. For example, if a leaf sample in a hydroponic tomato greenhouse shows low brix, often the first thing the consultant will recommend is raising the potassium-to-nitrate ratio until the brix reaches the target level. That way, nutrient problems can be avoided before the first signs of deficiency appear. Once visual nutrient deficiencies appear, the plant is already suffering and may not ever be able to reach its true genetic potential. Taking brix readings and making adjustments will help prevent problems before they happen.

So, in summary, Brix gives a measure of the plant's health, nutrient density, and ability to generate soil health.

Meaning of Brix test

Building Soil Organic Matter While Your Crop Is Growing -- webinar by John Kempf

Building Brix levels for healthier crops

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