yeast or coliform?

[Jen]

https://ibb.co/fDZT9pq  (Sorry, I can't get the image to embed for some reason.)

Try number 5 on making mozzarella.  Finally got a good stretch! 

Sadly, I noticed the curd mass getting really spongy.  I think it must be yeast for the following reasons:

Received raw milk yesterday from nearby farm.  Have made cheese several times with no problems at all.
With this batch, I made both an Alpine Tomme and cheese curds yesterday - same culture, same approximate temperatures.  Both seem fine.  At least I hope they are because we've already eaten half of the cheese curds!

Today, I made mozzarella.  Everything was going fine. I had drained the curds, and they were ready to stretch after one hour at about pH 5.3.  But! earlier while it was coagulating, I grilled a couple slices of homemade 2 day old bread on the stove.  Is that enough to cause what I'm seeing? I don't notice any smell, except a slight sourness that I usually smell when making mozz.  No off odors at all. I'm going to let it sit this afternoon and see if it produces a smell to help me identify it.

Thanks for comments.

[Bantams]

Probably coliform. Bread yeast doesn't do anything in milk.

[Jen]

Thanks, Bantams. I appreciate your response.

I have been trying to figure it out. See if this makes sense to you...

I was careful to get the milk home cold yesterday and made the cheeses right away, so the coliform didn't have a chance to develop before the thermo cultures took over.
The remaining milk I put in the fridge to make mozzarella and yogurt today. The yogurt was fine, because it's basically pasteurized in the making. Not so the mozzarella.

I went back and checked the temp of the milk in the fridge.  52 degrees!  (we're having a heatwave in Montana, above 100 every day, and clearly my little apartment fridge can't handle the hot weather.)  That probably makes it a perfect environment for bad bacteria. 

I am fine to pasteurize the milk before using it in the future, but I do have a question.  After having done a couple dozen makes, the difference between this particular raw milk and any other raw or store bought milk is astounding. The curd quality (at least to my inexperienced eye) is really like night and day. This milk just seems to firm up beautifully every time and doesn't shatter like the other milks I've tried.  Will I lose that particular quality if I pasteurize it?

This has been the first time I didn't make cheese on the day I received it, which is probably why I haven't run into it before.

Thanks again.

[OzzieCheese]

Not having the experience with raw milk but if you suspect the milk then home pasteurizing - Low Temp Long Hold method, is best but you will still lose some of your raw milk experience. At least you can be confident of milk safety. LTLT involves heating the milk to 62.5ºC/144.5ºF and holding this for 30 minutes. Make sure it stays over that for the entire time. Anytime lower at a lower temperature you have to start the clock again. After that, cool the milk as fast as you can to the culture adding temperature and start making cheese from there.

You are really lucky to have access to raw milk!

BTW making bread and making cheese on the same same is not a good idea as yeasts certainly do love the lactose (Milk Sugar) as it make the curd frothy. While not being a micro-biologist, I do agree that it does look like a coliform has got into your curds. Toasting bread won't cause that.

Here is a link on our forum
https://cheeseforum.org/forum/index.php?topic=10100.0

Hope that helps.

[Bantams]

I think that you will find freshly pasteurized (low-temp) milk to be quite similar to raw milk. Do be sure to add a bit of calcium chloride. 
Store bought milk is generally pasteurized at a higher temp and each day that it is stored results in a weaker curd.  It's very hard to find store bought milk that rivals farm fresh low-temp pasteurized milk. 

As for the coliform, it's really not your fault - it's the farm's problem. Their coliform counts should be 0, and they clearly are not.  Yes, a warm fridge is never good, but if you're experiencing coliform issues I would either find a new source or start pasteurizing.  Unfortunately coliform in raw milk is quite common, especially on farms that do not have adequate food safety training, proper cooling equipment, or proper sanitation procedures.  From what I've seen most producers do not test, and if state mandated it is usually just 1x/month.  It's actually quite easy to produce milk without coliform, but many producers seem to lack the knowledge and technique, and don't make cheese or test their milk so they are unaware. 

[Jen]

Thank you, both, for you replies.  It's very helpful and gives me a good strategy going forward.

Now I need to figure out a gentle way to tell my dairywoman. Montana just passed a law that allows farm producers with a small herd to sell directly to the consumer, which I have been waiting for for 10 years! This particular lady has had milk cows for over 30 years, raised a large family on raw milk. etc. But, no one has made cheese, as you said Bantams, and so they never noticed.  I am meeting a lady with goats this week for milk. She said she makes her own cheese, so that is very hopeful. I have to say that meeting dairy folk has been a real treat and I love buying my food directly from the people who produce it.

At any rate, it's a great learning experience and even a bad result is worth it if I can spend an afternoon making cheese! Thanks again.

[OzzieCheese]

I think that your supplier would want to know that what they are selling is potentially dangerous if they don’t know. I think you are very fortunate having raw milks available. Who would thought that Australians would be so risk adverse but apparently we are - well some of us anyway. I’d jump at the chance. We all have become so disconnected from our food source that we forget that milk doesn’t come in cartons.

[Jen]

I think so too, OzzieCheese. As I am her first customer, I hope that she solves the problem and continues to sell to me.  You're right.  Being able to buy raw milk is a real blessing. I want to take every advantage of it.

Yeah, the wild wild west ain't so wild anymore either.  A shame really. There was a long fight in my state to be allowed to sell and buy raw milk. I hope it lasts a long time.