Dairy Hygiene

What are the general things that milk is composed of?

Proteins

• Caseins (80%)

• Whey proteins

Lactose

Minerals

Fat

WATER MOSTLY (especially when diluted)

• Higher concentration of water in a product → better environment for microbial development

  • = shorter shelf life

** Ratio of fat and protein will vary between species

Remind yourself on how milk is processed and stored…

1) Raw milk is received

2) Filtered

3) Stored

4) Clarifier / separator → raw cream storage OR

5) Pasteurization

• Vitamin addition OR

• Homogenization

6) Pasteurized storage

7) Filler

8) Cold storage

9) Distribution

At what temperature should milk be stored at all times during the process?

BELOW 5 C

• Should be kept refrigerated after pasteurization no matter what

When considering hazards along the process of milk collection and processing, what are the main properties of milk we need to keep in mind?

Milk is a HIGHLY perishable product and requires processing shortly after collection

CANNOT BE STORED FOR MORE THAN A FEW DAYS

A number of hazards can be present in milk (from pre and post-harvest)

• Physical

• Chemical

• Biological

When can the highest amount of potential hazards be found along the milk production line?

In the HOUSING OF DAIRY CATTLE

• Animals need to be clean and well kept

• Parlor designed to prevent contamination and should be maintained / managed appropriately

• Animals not to be allowed in the sites where milk is stored, handled, or cooled

Where are the 4 main areas on a COW that could cause contamination in milk? What are the potential causes of this that may need correction?

1) Dirty legs

• Fecal splashing from dirty passageways

2) Dirty tail

• Loose feces

• Cubicles too small

3) Dirty flanks

• Poor beds

4) Udder

• Affected by ALL sources

In general, what are the sources of hazards in pre-harvested milk? How could these be prevented?

• Hygiene of the animals, environment, and workers

  • Solved by appropriate health plan

• Health of the dairy herd

• Quality of the raw milk

• Milking and pre-storage conditions

• Available storage facilities and technologies

  • All of these prevented by good farming practices:

    • Cleanliness of premises

    • Cleanliness of staff

    • Cleanliness of the animals

    • Pest control

Remind yourself how to perform a good, sterile milking routine:

“Strip, dip, dry, and apply”

• Strip

  • Wipe loose dirt from each teat and pre-strip (foremilk)

• Dip

  • Pre-dip and wait 20-30 seconds

• Dry

  • Wipe each teat with a single-use paper towel

• Apply

  • Apply teat cups 60-90 seconds after the first touch of each udder

Why do you strip the teat first before collecting milk?

• To eliminate the first milk, which will be contaminated

• To check if there’s any indication of mastitis

• To trigger suckling reflex of the teat to begin the milking process

When it comes to milking equipment, how do you avoid the buildup of residues? What does cleaning and disinfection include in general?

Needs to be able to prevent the buildup of milk residues: FAT, PROTEIN, and MINERALS

• Fat → Alkaline wash

• Protein → Alkaline + Cl wash

• Mineral → Acid wash

What cleaning and disinfection includes:

• Manual cleaning of exterior and parlor

• Internal cleaning

  • Circulation cleaning (“cleaning in-place (CIP))

  • Acid boiling wash (ABW) → single pass

• Bulk tank cleansing

Describe the process of circulation cleaning (CIP)…

Cleaner circulates through entire milk collecting pump, over and over again from the milk transfer line (see image)

• Same cleaner cycles through; this is why it is called “cleaning in place”

Cleaning process:

• Step 1) Rinsing

  • Done with WARM water at 38-43C

    • Protein residues in milk… if water too hot, proteins will denature and stick to inner surfaces of the tubing

    • Will cause a rough surface area, with places to harbor and facilitate bacterial growth

    • If water is too cold, the FAT content in the residues will harden… will do the same thing

    • So water needs to be at this warm temp range

• Step 2) Wash

  • Alkaline (+ chlorine) solution; can be done at a higher temp (60-70 C) for 5-8 minutes during circulation

Best for maintenance cleaning

Describe the proces of an acid boiling wash…

Cleaner only circulates through the milk collector once

• Cleaner is an acid; corrosive, so don’t want to keep the mechanisms exposed to that for long

NOT DONE DAILY

• Single flush

• VERY HOT WATER (start at 96C)

• MUST STAY ABOVE 77C

• Nitric / sulphanilic acid in the first few minutes

Best for big cleanings

What are some potential errors in milk equipment disinfection that could lead to contamination?

• Problems may occur due to:

  • Inadequate temperature

  • Inadequate volume of cleaner

  • Inadequate chemicals

  • Inadequate circulation and physical action (e.g. circulation too long – temperature decreases - deposits accumulate)

  • Blind ends in milk collector tubing

  • Failure to manually clean the bulk tank when necessary.

When problems occur – higher number of microorganisms (Bactoscan and/or total bacterial count)

Approach to bactoscan problems…

Keep in mind, if there is a high bacterial load of contamination of RAW milk, the most likely source is gonna be from the pre-milk farm end of things (cleanliness, milking technique, maintenance of machines, etc.)

What are some of the most common microorganisms to contaminate milk?

Streps - specifically S. agalactiae

Coliforms

Psychotrophs

Thermodurics

What are the most common sources of that bacterial contamination?

Udders

Environment

Dirty milking machine / poor wash up equippment

• Often the bulk tank

Failure of refrigeration

Match the source of contamination with the bacteria that comes from it…

Streptococcus agalactiea is a bacteria specific to the udder; so if you find it, you know its the udder specifically that is contaminated 

Coliforms -

• Come from fecal matter; can also be a potential sign of clinical mastitis, but usually that comes with other physical symptoms that would have to be reported. 

• If you see high numbers of coliforms in a bactoscan, with no other reported findings, its most likely they’re coming from a fecal-contaminated environment 

Psycotrophs -

• Thrive in colder temperatures; are indicative of a dirty environment (GENERALLY dirty, not fecal dirty); shows that there isn’t much cleaning happening (whether thats through dirty pens/ unchanged bedding) that allows these bacteria that like colder temps to thrive 

• Can also be caused by failure of refrigeration; chilling is cold but not cold enough to prevent the spread of psycotrophs, who can still thrive at 10 C (milk should be refrigerated below 5C at all times) 

Thermodurics -

• Can thrive in higher temps (40-50C), so if you’re getting them in your milk after collecting, this means they are surviving through the milk collector cleaning process 

• Indicates poor cleaning routine, resulting in a still-dirty milking machine 

Define what “raw milk” is…

Is defined as milk produced by the secretion of the mammary gland of farmed animals that has not been heated to more than 40C or undergone any treatment that has an equivalent effect

**“Raw milk is milk from any animal that has not been pasteurized to kill harmful bacteria. Raw milk can carry harmful bacteria and other germs that can make you very sick or kill you. While it is possible to get foodborne illnesses from many different foods, raw milk is one of the riskiest of all”. (CDC)

What zoonotic agents MUST be reported if found in an animal product according to List A of Annex I of the Zoonoses Directive EC 99/2003?

Salmonella

Campylobacter

Listeria monocytogenes

Shiga toxin-producing E. coli (STEC)

Mycobacterium bovis

Brucella

Trichinella

Echinococcus

Which microorganism is the biggest zoonotic threat when consuming raw milk?

MYCOBACTERIUM BOVIS

• Tuberculosis

• Comes directly FROM the milk itself

This and Brucella bovis

In high-income countries, what is the biggest source of contamination in dairy products?

Bacteria from FECAL CONTAMINATION

• So even in first world countries, milk is most commonly contaminated by coliforms

Keep in mind that antimicrobial testing is done quickly to determine whether or not milk still has medicinal residues in it…

What is the most common antimicrobial testing done during milk processing?

The Delvotest SP

• Principle:

  • Incubate a milk sample with media containing bacteria sensitive to what ever the cow had been treated with

  • If the bacteria continue to multiply:

    • Color change of bacterial growth occurs in media

      • Metabolic byproducts

  • If the bacteria does NOT multiply…

    • No color change = fail = bacterial growth was INHIBITED (means that there ARE antimicrobials in the milk and is not fit for human consumption)

What are the 3 different kinds of heat treatment you can do to milk? Which is the most popular?

1) Pasteurization - most common

• Holding Method

  • 62.8 °C to 65.6 °C

  • 30 minutes holding

  • Immediate cooling to <10 °C

• High Temperature Short Time 

  • 71.7 °C

  • 15 sec holding

• Milk must:

  • Be cooled immediately after heat treatment

  • Be phosphatase negative

  • Be peroxidase positive

  • Meet microbiological standards

  • Be packaged as soon as possible

• Records must be kept for 3 months

2) Ultra High Temperature (UHT)

• 135 °C

  • 1 second holding

• Milk must:

  • Be packaged immediately

  • Sterile containers

  • Aseptic conditions

  • Meet microbiological standards

• Records must be kept for 3 months

3) Sterilization

• Is the ONLY METHOD that actually kills all microbes

• Heated to greater than 100°C

• Milk must

  • Comply with turbidity test

  • Meet microbiological standards

• Records must be kept for 3 months