Category: Microbiology

Yoyo Swab Results

I have photographed the results of swabbing yoyos onto LBA plates. Of course this wasn’t an experimentally rigorous test and we can’t tell anything quantitative from it, but still it does appear that the “hand” swabs had visibly different community than the yoyos. Given that the hands had a ton of yellow colonies, I’m going to just assume that those were mostly Micrococcus luteus, since M. luteus is commensal on skin and whenever I’ve sequenced colonies that looked like that in the past they were M. luteus (and most likely contaminants from skin).

Other notable observations were:

The hand replicates were Doc’s left and right hand. One of them seems so have had way more bacteria than another… although again our methods weren’t quantitative (I could have just so happened to have swabbed the one chunk on his hand that had all the bacteria, etc).

The negative controls did not have any growth whatsoever – so I guess my sterile technique is still pretty good.

And now, the results!

Hands (“positive control”):

LBA Plates
LBA Plates

Wooden yoyo:

LBA Plates
LBA Plates

Metal (aluminum) yoyo:

LBA Plates
LBA Plates

Plastic (delrin) yoyo:

LBA Plates
LBA Plates

Negative Controls (the same water and swabs we were using for the rest of the swabs, but without having swabbed anything):

LBA Plates
LBA Plates

Furry Little Coat of Mold

Our homemade brie is successfully growing its furry little coat of mold! And just look at how different they look compared to when I first took the curds out of the forms!

Our homemade brie is successfully growing its furry little coat of mold
Furry Cheese

They’ve really flattened out. I didn’t even notice this until I looked back at that old post!

Trying our hand at brie now
When I first turned the curds out of the forms… they were so much taller and fatter back then!

However, I did hit a bit of a snag, which I think I should warn everybody about. I was following instructions from a zine that said, “when you see mold, wrap it in cheese paper” so I did just that. The zine then went on to describe all the terrible horrors that await the person who waits too long to wrap their cheese (and showed photos of drying mats tearing the mold off of the surface of the cheese, thereby ruining it). Nowhere did it mention it would be a problem to wrap the cheese too early.

Turns out this was slightly misleading. I interpreted this to mean, “wrap the cheese as soon as you see even a microscopic hint of mold,” when actually what they meant was “once the cheese is completely covered with a thick blanket of mold.” The problem with covering the cheese with cheese paper as early as I did is that the moisture sitting on the cheese where the paper is touching it will actually inhibit the mold growth (which is ironic, as mold will also fail to form if there’s not enough moisture).

Luckily, I was so excited to see how the mold was coming along that I unwrapped it to take a peek and noticed that the sides were covered with a luxurious coat, whilst the tops and bottoms were patchy-to-completely-bare. Concerned, I looked up a second opinion on brie making, and saw that the consensus was to wait until your brie is completely covered before wrapping it. Whoops! So I unwrapped them and returned them to the casserole dish that had previously been their mold-making home. There, I hoped they would still form the mold all over, as if I hadn’t ever wrapped them in paper.

Luckily, it would appear that they have quickly recovered from this error, as you can see in the photo above (taken about a week after discovering my error). I don’t know what this means for the aging time, to be honest. I suppose I’ll have to feel it out. By the original estimates, they should be ready next week at the earliest, but they are supposed to age for ~4 weeks after getting wrapped so I think this moves things back a bit.

So let this be a warning to all you would-be cheesemongers out there: wait until your brie is completely covered in mold before you wrap it in cheese paper, or meet the same fate! No matter what your zines say.

Raw Versus Pasteurized Milk for Cheddar

As you might recall, two months back I started some batches of cheddar. I was really curious to know how different the cheese would be using raw versus pasteurized milk, and whether I would be able to perceive that difference.

It has now officially passed the minimum recommended time period to age the cheddar, so we cut one of each open to taste. I know that I said we had planned to wait four months before eating it, but I was just too curious. I mostly needed to know if it was a horrible disaster, but also I wanted to know if the two chesses were any different.

Homemade cheese with homemade bread.
I also made some bread for the occasion

I have to be honest, I wasn’t really expecting there to be a huge difference. I thought there would probably be some subtle, nuanced flavors in the raw cheese that the pasteurized cheese was lacking, but that they would be overall comparable.

I. Was. Wrong.

Homemade cheddar cheese.

The two cheeses were incredibly different. Monumentally different. They tasted nothing like the same cheese. The raw milk cheddar was pungent, complex, flavorful, sharp and delicious. The pasteurized milk cheddar was also tasty, but much more understated and mild, and did not have a smell.

I also gave the cheese to my siblings to try, and many of them pointed to the raw cheese and said “That one is amazing, what is the difference between them?”

So, overall, the raw cheese seems to have won the popular vote. But I do still have a soft spot in my heart for the pasteurized cheese. It still tasted really good, at least as good as a nice store-bought cheddar.

Why did they taste so different? Well, I can only imagine that it was a combination of the flavor changes introduced by the pasteurization process itself, but also because there was a much higher diversity of bacteria in the raw milk cheese. I did only add one species to the milks, after all, so the pasteurized milk cheddar was basically a monoculture.

I think this had to have been a large contribution, because the difference was so clearly above and beyond the minor flavor changes that come from pasteurization. Such an unexpected result! But also, so exciting!