Grades aren't a mystery. Each one tells a story, if you know how to read it.
There are three main types of bacterial grades: Coliforms, Thermodurics, and Bactoscan. Each points to a different kind of hygiene issue, or a different kind of screw-up.Let's break them down. Have a read here and check in with Max, our grade wizard.
Coliforms: What They Are (and How to Kill Them)
Coliforms are the stinkers, literally. These bacteria love warm, dirty, milky places. Think cow
manure, test bucket hoses, and dodgy seals.
What they tell you:
There's milk soil somewhere in the plant. Often, it's in one spot, a hidden crevice, a blocked
jetter, or a cluster that didn't get washed properly.
Usual suspects:
• Blocked jetter = dirty liner
• Perished cone seal= cheesy joint
• Stirrer paddles = sneaky build-up
• Cold water washes only= coliform paradise
• Clusters dropped in the crap = instant grade
• Split liner = cheese in the air line
What to do:
• Sniff test: Coliforms stink. Don't be shy-your nose is your best tool.
• Hot wash daily: Chlorine and heat kill coliforms fast-if they're used properly.
• Inspect: Don't just look. Touch, scrape, smell.
Pro tip: If milk's going where it shouldn't, namely a split liner - or water isn't going where it should, namely a blocked jetter - coliforms are likely.
Thermodurics: The Survivors
These tough bugs don't just survive hot washes - they survive pasteurisation. And that makes them a massive problem for manufacturers.
What they tell you:
Your cleaning's not reaching certain spots - usually the tops of milklines or inside perished rubberware. Or you've got protein deposits baked on like burnt milk in a saucepan.
Usual suspects:
• Protein film on vat walls or floors
• Old milk soil on top of milkline near the ends
• Rubberware that's past its use-by
• Silage bugs (some are thermoduric spores)
What to do:
• Scrub top of milkline and boost your recirculation and contact time
• Replace rubberware that leaves black marks when scraped
• Improve alkali contact time (1-2 minutes won't cut it)
Pro tip: Your Milk Company laboratory can tell you if the grade's caused by spores (environmental), which points to silage or contamination - not your plant.
Bactoscan: The Big Picture Grade
Bactoscan measures total bacteria - all types. It doesn't care what they are, just how many. A high Bactoscan means there's bacteria somewhere in the process, and it's adding up fast.
What it tells you:
Something is letting bugs in, or not killing them off. Could be plant hygiene, slow cooling, or mastitis.
Usual suspects:
• Hidden hygiene fault (especially milkline joints or claws)
• Poor pre-cooling or refrigeration
• Mastitis (especially Strep uberis early in the season)
What to do:
• Start a full inspection (see Section 11)
• Compare somatic cell count: If it's high too, you may have a cow issue
• Ask your Milk Company laboratory: If the Bactoscan is bad, they should do a plate test and tell you if it's hygiene or mastitis
Reality check: Bactoscan isn't just about your cleaning. It reflects the whole system – from cow to tanker.