In a wide array of agricultural publications, I’ve been reading about something called “Brix.” As in: We need “high Brix levels in our forages” to support good cattle growth.
This Brix has nothing to do with the old-fashioned bricks for building houses, and it’s not a misspelling of the word “Brexit” which has appeared in a few newspapers recently. This Brix is a measurement, an intriguing intersection of things like forages, silage, wine, fruit juice, jams, livestock nutrition, aquariums, colostrum and garlic. Garlic?!? Hmmm …
Brix is actually a measurement of the amount of sugar in water, more or less. It’s a technique with its roots in the history of wine. Winemakers had long known that good wine requires grapes with a high sugar content, but for ages vintners had no way of objectively measuring the sugar content of their grapes before they put them into the barrels to ferment – which caused a lot of guesswork where a wrong guess could result in huge losses of money and reputation.
In the early 1800s, the German A.F.W. Brix (A.F.W. stands for Adolph Ferdinand Wenzeslaus) devised a technique to estimate the amount of sugar dissolved in water by measuring the specific gravity of that water. For example, 1 degree Brix equals 1 gram of sucrose (table sugar) dissolved in 100 grams of water. Although the Brix score was potentially very useful, measuring the specific gravity of a liquid was rather cumbersome.
But there was an alternative. Unlike specific gravity, measuring light is not cumbersome. Dissolving sugar into water changes the specific gravity of the water, and it also changes the optical properties of that water. This means light passing through the water will bend (refract) at an angle determined by its sugar content. And it’s relatively easy to measure refraction using a small hand-held device known as a “refractometer.” Put a couple of drops of liquid onto the device, point it toward a light source, hold it up to your eye, squint into the eyepiece, and read the scale.
Chemists and engineers have run lots of tests to calibrate the angle of refraction with the sugar content, so today’s refractometers can give reasonably accurate Brix values. And refractometers are not expensive. Simple manual ones may cost less than $50, although a complex digital refractometer will run upwards of $300.
What are common Brix numbers? Although the official definition expresses Brix in “degrees Brix” (referring to the refractive index), Brix values are usually expressed as a percent, as in 8.4% Brix. This is the common terminology we see in American publications. In practice, Brix values can range from 0% to higher than 70%.
Here are some typical Brix values in foods: wines at 14% to 19%, grapes at 20% to 25%, carbonated sodas at 5% to 15%, concentrated fruit juices at 42% to 68%, condensed milk at 52% to 68%, jams and jellies at 60% to 70%.
An important concept about Brix, however, is that it doesn’t always refer to sugars. Brix values depend on any dissolved solids in the solution: sugars, starches, acids, proteins, pectins, free amino acids, salt, etc. This allows Brix numbers to be used in a wide variety of situations. For example, aquarium enthusiasts can use Brix to estimate the level of salt in their saltwater fish tanks.
Definitely no sugar there. Another example more related to agriculture: Researchers have used Brix to evaluate the quality of colostrum by estimating its level of antibodies (immunoglobulins; for the technically minded, specifically, IgG). Brix values for cow colostrum range from 15% to 30%, with a low-end cutoff for good colostrum at 22%. (Interesting: High-quality bovine colostrum has Brix values similar to high-quality wine grapes. I’m sure there’s a joke in there somewhere.)
Now let’s relate Brix to forages. We can test any forage for a Brix value. Take some green material, like grass blades or the vegetative material of any forage, squeeze it to extract some liquid (sap), then run a Brix test on that liquid.
How useful is that number? The articles in those popular magazines claim great use because they all accept the same premise – that higher Brix numbers mean higher nutritional quality. The logic goes something like this: high Brix values mean high levels of soluble sugars and, by extension, more available energy and higher nutritive value. Therefore, those articles say, high-Brix forages are necessary to fatten calves and lambs and support high milk production.
But is this really true?
Let’s step back for a moment. A Brix measurement of a leaf does indeed give a reasonable indication of the level of soluble items in that leaf (recall that any soluble molecules will influence Brix), and folks tend to assume those items are sugars. But in the plant world, things are often more complex than they first appear. Many factors influence the level of soluble sugars in a plant: forage species and variety, stage of maturity, soil fertility, weather, time of day, the part of the plant tested, etc.
For time of day, we know that green plants do one thing rather well: photosynthesis. This requires sunlight, of course, and it results in the direct production of simple sugars. As the sun moves across the sky, these sugars tend to accumulate, reaching a peak in the late afternoon. Then these sugars are transported south toward the roots. So when should you take a Brix reading – in the morning, mid-day, afternoon or at night?
Also, since forages transport sugars from their leaves to the roots, the stems will sometimes show higher Brix readings than the leaves. Which is a bit counterintuitive.
Brix readings, however, may have some practical implications for harvested forages. High Brix readings suggest that the forage will make good silage. Why? When plants are cut and put into a silo, the ensiling process depends on bacterial fermentation, primarily of the available sugars and starches. The faster the fermentation, the quicker the pH will drop and the better chance the silage will be made properly. Soluble sugars ferment quicker than starch. For example, the high-sugar perennial ryegrasses tend to make better silage than their more mundane relatives.
On the other hand, higher sugar levels may not be great for making hay. Why? Because microbes thrive on sugars. If forage is cut for hay and there is no rain, there is no problem. But if the drying hay lays in the windrow and it rains (not just a theoretical possibility), high sugar levels can accelerate microbial growth and result in lower-quality hay by the time it gets baled and hauled to the barn. This is just a hypothesis (mine), but it seems plausible – a good topic for some research.
Back to our livestock. Cattle are not humans; there’s no guarantee of a sweet tooth. Our cattle have palatability preferences, of course, but it’s not clear that sugar levels are truly related to those preferences (unlike humans, of course.) And palatability is really just a choice between multiple selections. The important characteristic is total feed intake over 24 hours. While we can easily observe rapid intake of highly palatable, high-Brix forages during the day, does that translate to increased total intake over 24 hours? Do higher Brix values equate to higher daily dry matter intakes (DMIs) or higher production? Not necessarily. Recall that higher sugar levels usually occur concurrently with higher levels of protein and lower levels of fiber. There are a lot of confounding factors that influence intake and production, and there’s no good data that demonstrates high Brix readings by themselves improve animal production.
And here’s the big thing about nutritive value. Ruminants like cattle handle sugars quite differently than humans. In cattle, those soluble sugars never reach the small intestine. High Brix readings mean higher amounts of sugars enter the rumen. The rumen microbes happily ferment these sugars quite rapidly, even faster than the starch in wheat and corn. While this is excellent for capturing excess nitrate nitrogen from highly fertilized forages and converting that nitrogen into protein, this is nutritionally helpful only to those animals who actually need the extra protein.
A potential drawback of sugars in the rumen is the increased risk of acidosis. The rapid fermentation of sugars results in lots of acid formation in a short period of time. This can usually be buffered by the rumen solution, but not always. If the rumen pH drops below 6, the fiber-fermenting bacteria suffer, and the digestibility of the fiber declines. Which is not necessarily a good thing in a forage-based diet. Full-blown acidosis is life-threatening to a ruminant, but even subacute acidosis will reduce production and is something to be avoided.
So are high levels of soluble sugars a good thing? Not necessarily. And not all high-quality forages contain high levels of soluble sugars. Also, we’ve seen that Brix values can vary all over the map due to many factors. Our bottom line is: The world of forages and nutrition is more complex than a simple Brix number.
Now the final item: garlic. I mentioned garlic in the opening paragraph. How is garlic involved with Brix readings and livestock nutrition? Simple, anyone who takes Brix readings must first obtain a sample of plant liquid by crushing the leaves. And the most common tool for doing this? A garlic press.
