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 the Grade Guru.
What causes a coliform grade?
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.
What causes a thermoduric grade?
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.
What causes a high bactoscan?
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 chapter 13)
• 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.