Chasing Coliform Counts

I was recently visiting England to attend “The Science of Artisan Cheesemaking” conference and had the great additional luck to visit an amazing farmstead creamery- Hill Dairy in Somerset. Not only was the facility quite possibly one of the most well thought out and constructed small creameries that I have ever visited, but owners Will and Caroline Atkinson, were as charming and lovely as their picturesque English farm. Since I got back to the US, we have been corresponding about a problem that Hill Dairy was experiencing both during my visit and on and off for a good part of this fall. A problem, unfortunately, that caused the loss of many batches of cheese milk and is a problem that plagues many farmstead cheesemakers (sometimes even without their knowing). High coliform counts.

3M coliform petri film with count at about 400cfu/ml (black dots from Sharpie marker on a few) look for a red dot surrounded by or up against an tiny air bubble. each dot with air bubble is one cfu.

First a bit about the large bacterial family called coliforms. These microbes live in the environment of the farm, especially bedding, feed, and soil. But some of them also live in the lower intestine (not only of cows and goats, but of people too) the most well-known being Escherichia coli, better known by its abbreviated name “E. coli”. The presence of E. coli in milk or cheese can be translated as the presence of feces, that’s right, poo. While E. coli and poo in milk are not desirable in any circles, it doesn’t necessarily mean that the milk is unsafe. It is the ne’re-do-well coliform cousin E. coli 0157:H7 that can wreak horrible damage when ingested. (There is another variant that surfaced recently in Germany that is just as nasty and there will no doubt be more variations in the future that will cause horrific food borne illnesses, sickness, and death). So while coliforms do not necessarily mean the presence of pathogens (illness causing microbes) their numbers are a good gauge of milk cleanliness. The higher the general coliform count, the higher your odds that some might be bad.

Currently most data say that high quality raw milk should have fewer than 10 cfu’s (that’s colony forming units) per milliliter of milk.  Some states allow for higher counts and the “fewer than 10”number is somewhat arbitrary, but let’s pretend for now that it’s a great standard. Here at our farm our petri-film plate counts (done on every cheese batch – see my previous posts if you want to know how to do these) show our total coliforms at usually 3-5 cfu’s per ml. Awesome, right? Well, when I got back from England our counts shot up to over 400cfu/ml.  Fortunately for both us and Hill Dairy, tests showed that none of the coliforms were from fecal sources, no E. coliforms. (You can buy petri film plates that will grow E. coli’s in a different color than regular coliforms). Interestingly, but not surprisingly, our APC (which counts total bacteria numbers) didn’t look that bad – until you looked closely and could see that there were tiny air bubbles all over the plate (from the gas produced by the coliforms) and these bubbles had lifted the film from the plate – making it look as though there were not that many colonies growing.

Aerobic plate count showing red dots of bacteria colonies (cfu’s) and lots and lots of tiny air bubbles from coliforms making the plate “uncountable”.

So what do high numbers of “harmless” coliforms do to milk and cheese? Well, these guys eat lactose – that’s milk sugar, (as do starter cultures) and produce both lactic acid and carbon dioxide – that’s gas. The problem with them is that they grow very fast and can often out-compete the added starter culture during a slow fermentation, just like what is done to make most fresh cheeses and lactic set bloomy rinds (like the Atkinson’s were making – and yes it is legal to make them with raw milk in the UK). At Pholia Farm, we make long-aged, low moisture cheese that use a faster acid development and rennet, so we would not have known about our high coliform counts if we were not doing routine lab tests on every batch. While these coliform types are unlikely to make our cheese unsafe, it tells us that something is far from ideal with our process – something that could lead to unsafe food. We don’t only make cheese, we drink our raw milk – we care that it is of the best quality possible for many reasons.

Okay, so both our farm and Hill Dairy had much higher than normal counts, what did it mean and what did we do about it to resolve the problem? The most common causes of high coliforms are dirty teats, poor milking technique, and dirty equipment. While this may seem like an easy fix, when your counts suddenly go from great to horrendous, it can be very confusing.  So let’s go over a step by step procedure for trouble shooting coliform counts – with as little financial investment as possible!

  1. Observe that animals are coming into the parlor relatively free of manure and debris – dairy clipping udders can help.
  2. Verify that established teat and udder cleaning methods are being performed properly and that udder cleaning solutions and sanitizers are effective.
  3. Verify that milking equipment with parts that need replacing, especially rubber parts, are up to date for recommended replacement times.
  4. Verify that cleaning steps for equipment are effective – this includes chemical strength and effectiveness for your water type, temperatures, time, air slug velocity, etc. Swabs can be taken at various points in system and cultured for total bacteria counts to verify effectiveness.
  5. Perform “hyper-cleaning” following guidelines from chemical manufacturer or other dairy representative. This often includes a double strength, double time cleaning and manual cleaning to verify the removal of bio-films and residue that might have occurred from less than ideal parlor practices.
  6. Verify milk chilling process, if used (even with proper chilling, high enough coliform counts will be a problem in lactic technology cheeses)

Don’t be surprised if trouble shooting takes place over many days before you completely conquer the problem. All it takes is one step to be missed, and the problem reasserts itself. For example, our problem seems to have come from our neglect (later in the season) of dairy clipping our ladies udders, combined with wet weather, combined with me forgetting to replace a couple of rubber parts inside of the milking claws , combined with a bit too casual milking and udder cleaning techniques. I would fix one problem, but not all problems at one time. Everything needed to be zeroed out, you might say, before our counts went completely back to our normal low.  It took several weeks of implementing new techniques and replacing parts and hyper-cleaning to shape things back up. During that time the count dropped from the 400, to 100 plus, then to the high 30’s, and finally to under 10.

Coliform petri film showing 3 cfu’s (circled with black ink). This is great!

If you experience a similar extended issue, here are some things you can do so that you don’t lose product, and future income, while you whip things back into shape:

  1. Pasteurize the milk.
  2. Thermize, aka heat shock, the milk (lower temperature than pasteurization, not recognized in the US, so cheeses made from thermized milk are not considered pasteurized)
  3. Switch from lactic cheeses (such as surface ripened and fresh soft) to an aged, quickly cultured and rennet style cheese. (Verify that no E. coli is present)
  4. Switch from freeze-dried direct set culture to bulk starter or mother culture that will provide a faster growing starter bacteria population. (if coliform counts are too high, though, this may not be enough)

Remember that if you are not testing each batch of cheese milk and are making a rennet coagulated, quickly acidified cheese, you may never know that your milk is less clean than it could be! If you do experience a problem, don’t feel alone and remember that keeping sanitation standards high on the small farm, or any farm for that matter, is an ongoing, major challenge. It is a great reminder of how quickly things can change – for the worst.

5 thoughts on “Chasing Coliform Counts

  1. Your approach to dealing with the E-coli count reminded me of the calm, professional and caring approach of an emergency room physician. The upshot shows that simple, step-by-step measures taken with a cool head can be amazingly successful. Bravissima!

  2. My father-in-law is a microbiologist. His lab tests bacteria in milk. They are going to teach my husband and I how to do it. The lab isn’t State certified. I thought they were, but they know how. He is also going to teach me how to fecal tests, as apparently we can do that ourselves.

    Peggy

  3. I will have to read this article after milking and chores. Sounds super interesting! And yes, if you have nursing training that is a very big plus.

    Peg

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