A Certificate of Analysis arrives on your desk, and the first thing you notice is that it is not written for people like you. Your job is not to replicate the test; your job is to interpret whether the numbers say yes or no to your order. Misreading a COA means you might accept the wrong product, reject a good supplier, or miss a detail that disrupts production.
Whether your team is building capability to read and compare Certificates of Analysis or needs help interpreting one that just landed in your inbox, contact One Source Food Solutions to talk through what the numbers mean.
What Is a Certificate of Analysis and Why It Matters
This document is prepared by an analytical laboratory that reports the measured composition of a specific lot of ingredient. When the COA shows that a lot of tomato paste measures 31 percent NTSS, pH 3.8, and Bostwick 140, your QA team uses those numbers to accept or reject the lot.
A Certificate of Analysis is lot-specific and carries legal weight. Under the FDA’s preventive controls rule, receiving facilities must verify that incoming ingredients meet specifications through a risk-based supply-chain program, and the COA is the primary tool for that verification. A co-packer who accepts an ingredient without reviewing it, then discovers mid-run that the color is off, loses days of production and cleanup. Having reviewed it at the dock would have caught this.
What Are the Key Numbers on a COA: NTSS, pH, Bostwick, and Color
What Is NTSS (Natural Tomato Soluble Solids)?
NTSS measures the concentration of dissolved solids in tomato juice and is expressed as a percentage. A higher NTSS means a more concentrated product, and concentration affects both yield and price. Bulk and aseptic paste in drums typically carries 31 percent NTSS, while canned or pouch paste is often 24 percent NTSS. Knowing the NTSS of the paste you ordered versus the paste you received is the first comparison to make.
What Does pH Tell You About Tomato Paste?
pH measures acidity on a scale from 0 to 14, with lower numbers meaning more acidic. Tomato paste pH typically ranges from 3.5 to 4.0, and your finished product’s safety and shelf life often depend on the incoming ingredient being within a narrow pH window. A paste arriving at 4.2 when your specs require 3.8 to 4.0 can seem like a small difference, but if your product is shelf-stable sauce rather than a high-acid canned good, that tenth of a point matters to your preservation strategy. The COA tells you whether your processing assumptions hold.
What Is Bostwick Consistency?
Bostwick consistency measures the flow behavior of paste, expressed in millimeters of distance the paste flows in 30 seconds under standardized conditions. A higher Bostwick reading means thicker paste that does not flow as readily. Paste from one supplier might run at Bostwick 140, indicating a thicker product suitable for applications where consistency is important, while paste from another might test at Bostwick 165, requiring different pump settings or production adjustments. Consistency determines how the product behaves in your line, and a Bostwick that is significantly different from your specification can mean retooling or rejection mid-production.
What About Color?
Color is also on the COA, usually reported on a numerical scale or by visual comparison. Tomato paste color varies seasonally, influenced by the ripeness of the fruit at harvest and processing conditions. Your finished product’s color expectation may require paste within a tight range, or it may tolerate variation. A COA showing color 120 on the scale you specified tells you the lot is in spec; the same reading on a COA where you specified 110 to 115 tells you the lot is too dark for your purpose. Shade differences that seem minor to the eye become very material when they affect how a finished pizza sauce or ketchup is perceived by consumers.
Understanding what each number controls in your process is what turns a COA from an abstract document into an operational tool.
Where COAs Come From and Who Conducts Tests
Laboratory tests come from a third-party source, not the supplier’s internal lab. The supplier arranges and pays for testing, then distributes the results to you. The laboratory should hold AOAC International accreditation, and the COA should identify the lab, date, method used, and results. For tomato ingredients, tests include solids, pH, consistency, color, and often heavy metal analysis and microbial verification.
A COA without a lab name, date, or clear methods is a red flag. If a supplier cannot provide results from an accredited laboratory, you lack the third-party verification that your supply-chain program requires.
The testing method matters because different procedures yield different results. If supplier A uses method X for NTSS and supplier B uses method Y, their results may not be directly comparable. A good supplier will retest at no charge if you question a result; a defensive response suggests a quality or relationship issue.
A COA represents a moment in time for a specific lot.
What Red Flags Signal Supplier or Quality Issues
Several patterns warrant additional questions. Incomplete data in a Certificate of Analysis (missing Bostwick or microbial results when you normally receive them) suggests the supplier is ordering bare-minimum testing. Ask why before accepting.
Inconsistency across lots is more telling. A paste supplier’s NTSS swinging from 29 to 32 percent on successive lots, while within range, might indicate loose processing controls upstream. Documenting this variation helps you spot trends.
Results that look too perfect warrant skepticism. Paste that measures exactly 31.0 percent NTSS, 3.8 pH, and Bostwick 140 on ten consecutive lots is statistically improbable.
Defensive behavior matters. A supplier who cannot explain an out-of-spec result or who avoids retesting suggests they do not stand behind their product.
Finally, a discrepancy between the COA and what you observe when the ingredient arrives (the paste looks too dark even though the COA shows normal color) warrants investigation. The sample the lab tested might not be representative of the entire lot.
Patterns over time show real signal.
How to Compare COAs From Different Suppliers
When evaluating new suppliers, normalize the testing first: ensure all COAs use the same methods so results are comparable. A spreadsheet with NTSS, pH, Bostwick, and color for each supplier and your specification range shows clearly which product fits your needs. A supplier offering 26 percent NTSS is not interchangeable with one offering 32 percent, even if the price is lower, because you would need more of the lower-solids product to hit your finished-product concentration.
Over three or four lots, you see which supplier’s results vary more. A supplier whose Bostwick runs between 135 and 145 is more consistent than one ranging from 125 to 155, and consistency affects how predictably your process runs. Our guide to how to qualify a new ingredient supplier covers the full evaluation process that lives behind your comparison.
Price should be adjusted for concentration. Comparing cost per finished pound is far more useful than cost per incoming pound. A side-by-side comparison file is the practical output of reading COAs well.
When a COA Doesn’t Match Your Specs
Do not accept an out-of-spec lot without answers. A Bostwick of 115 when you specified 140 to 160 is out of spec, and accepting it creates legal and operational risk. Contact the supplier, ask whether the result is correct, and request a retest if you question it. A professional supplier will retest at no charge.
If the supplier confirms the out-of-spec result and the reason is temporary and correctable, you might accept on a one-time basis with documentation. If they cannot explain it, reject the lot. Discovering the issue during an audit or customer complaint costs more than catching it at the dock.
Act on out-of-spec results.
Connect With One Source Food Solutions
Most teams discover what a Certificate of Analysis really does only after they have failed to read one carefully. The missed detail that surfaces mid-run, the supplier inconsistency that was visible in the COA file, or the quick rejection of a perfectly good lot because no one understood the numbers: these are the moments when reading it well starts to feel urgent.
At One Source Food Solutions, we provide a Certificate of Analysis with every quotation and shipment, and our team can walk you through what the numbers mean, what patterns to look for, and why the details matter to your operation. We have seen every question that comes up when a COA lands on a QA team’s desk, and we know that sourcing confidence starts with transparency.
If you are building your team’s capability to read and compare Certificates of Analysis, or if you receive a COA and want to talk through what it means, call One Source Food Solutions at (360) 887-9430 or reach out through our contact page. We are here to help you source with confidence.