Brix refractometer to monitor silage fermentation offers farmers a rapid way to gauge sugar levels in forage and anticipate fermentation performance. Readings can signal both healthy and problematic fermentation, depending on oxygen exposure and pH changes. Used alongside quick field pH checks, it helps reveal whether sugar use is beneficial or due to spoilage—guiding timely adjustments in silage management.
Feeds Specialist and Nutritionist
Dellait Animal Nutrition and Health
A Brix refractometer is a simple, yet precise optical instrument used to measure the concentration of dissolved solids, primarily sugars, in a liquid sample. In forage and silage work, results are expressed in degrees Brix (°Brix). In pure sugar solutions, 1°Brix equals about 1 g of sucrose per 100 g of solution, but in plant juice, the reading represents all soluble solids, including sugars, amino acids, salts, and organic acids.
The refractometer works on the principle of light refraction, light bends when passing from air into a liquid. The degree of bending, called the refractive index, increases as more dissolved solids are present. The device has a prism where a drop of plant juice is placed; light passing through the sample is measured either via an optical scale (in handheld analog models) or an electronic sensor (in digital models), and the result is instantly displayed in °Brix.
WHY BRIX MATTERS IN SILAGE
Sugar content is a key driver of fermentation. Lactic acid bacteria (LAB) convert soluble sugars into lactic acid, lowering pH and stabilizing the silage. Higher sugar levels before ensiling generally lead to faster and more complete fermentation; low sugar levels can slow the process and increase the risk of spoilage.
Measuring °Brix in freshly cut forage gives farmers a rapid estimate of fermentation potential before chopping, wilting, and packing. The refractometer is portable, requires only a few drops of juice, and provides results in seconds, making it ideal for repeated field checks during harvest and for follow up testing 24–48 hours after ensiling to track sugar use (Table 1).
BRIX CHANGES DURING NORMAL FERMENTATION
Before ensiling, high Brix values indicate plentiful fermentable sugar. As fermentation progresses, sugars are consumed and Brix declines. A rapid early drop often signals active LAB growth, particularly in inoculated silage (Table 2).
WHEN BRIX CAN MISLEAD: POORLY PRESERVED SILAGE
A falling Brix reading is only a sign of good fermentation when the silage is well compacted, sealed promptly, and kept airtight. If oxygen enters, due to poor packing, delayed covering, or damaged plastic, aerobic microorganisms (yeasts, molds, aerobic bacteria) can dominate. These organisms also consume sugars, but instead of producing lactic acid, they generate heat, carbon dioxide, and ethanol. As a result, pH stays high, fermentation fails, and nutrient losses mount.
Early sugar depletion can look similar in good and poor silage, but the cause is different. Without a rapid pH drop below 4.2, protein breakdown accelerates, heating develops (>35–40 °C), and molds appear quickly (Table 3).
SAMPLING & MEASUREMENT PROTOCOL
To get accurate readings:
• Collect representative samples across the field, avoiding extreme patches.
• For fresh grass, freeze for about 6 h, then thaw to release juice.
• Squeeze juice from ~200 g of forage and place a few drops on the prism.
• Calibrate the refractometer with distilled water at ~20 °C before use; allow samples to reach temperature equilibrium before reading.
Take an initial reading before ensiling, then repeat at 24–48 h, and if possible, at one week. Comparing inoculated vs. untreated silage over time shows how quickly sugars are used.
PAIRING BRIX WITH A QUICK FIELD PH CHECK
Brix shows sugar supply, but not whether it’s being converted into lactic acid. A simple field pH test help correct that misinterpretation:
1. Collect a small silage sample, either freshly chopped forage or material from a mini silo/bale.
2. Make “silage tea”, chop finely, place a handful in a clean jar, add 4 parts clean water to 1 part forage, stir, and let sit a few minutes.
3. Measure pH by using narrow range (3–6) pH strips or a pocket pH meter.
Interpreting Brix + pH together:
• High Brix + High pH → Sugars available but fermented slowly or stopped.
• Low Brix + Low pH → Good fermentation.
• Low Brix + High pH → Sugar loss from spoilage, not beneficial fermentation.
Target pH:
• Grass silage: <5.0 by day 2–3; ≤4.2 when stable.
• Maize silage: often stabilizes closer to 3.8.
ECONOMIC VALUE OF PAIRING A BRIX REFRACTOMETER WITH A PH METER
A good handheld Brix refractometer and a reliable pocket pH meter together represent a modest, one time investment of roughly $200 or less. For that cost, farmers gain the ability to detect fermentation problems early, before they lead to major silage losses.
Even a small loss of 5% in a 500 ton silage inventory equals 25 tons of feed. At $60–$100 per ton, that’s $1,500–$2,500 gone, easily more than ten times the cost of the equipment.
Benefits for inoculant management:
• Confirms whether inoculants are actively driving fermentation.
• Brix readings show the speed of sugar consumption.
• pH readings confirm whether that sugar use is translating into rapid acidification.
• Detects underperformance early enough to adjust inoculant type, dose, or application method before the next harvest.
Bottom line: For less than the cost of a single spoiled bale pile, these two simple tools can protect silage quality, ensure inoculants are doing their job, and deliver a return many times over each season.
LIMITATIONS
A refractometer measures total dissolved solids, not sugars alone. Organic acids and alcohols formed later in fermentation can affect readings, so Brix is most reliable in the early stages. It should be seen as a rapid screening tool, not a replacement for lab analysis.
Used correctly, especially when paired with simple pH checks, a handheld refractometer can help farmers monitor fermentation in real time, evaluate inoculant performance, and make timely adjustments to sealing, compaction, or sugar supplementation.
References
1. García, Á. (2025). Silage inoculants can offer nearly three to one returns. Dellait Animal Nutrition & Health Knowledge Center. Retrieved [Access Date], from Dellait website researchgate.net+14dellait.com+14dellait.com+14
2. Billman, E. D., & Soder, K. J. (2024). Validation of Brix for predicting sugar concentrations of alfalfa and orchardgrass herbage. Applied Animal Science, 40(4), 437–445. https://doi.org/10.15232/aas.2024 … academic.oup.comsciencedirect.com
3. Soder, K. J., Billman, E. D., Horst, J., & Balk, K. (2025, March 17). Can Brix predict forage quality? Hay & Forage (USDA ARS perspective). Retrieved [Access Date], from Farm Progress website hayandforage.com
