Listeria Prevention for The Home Cheesemaker
How do you get listeria or other foodborne illnesses?
For the home cheesemaker who might be worried about contaminants like listeria, prevention is key to ensuring that your cheese is safe.
Food safety is a critical part of all food preparation and production, but it might be even more important when making cheese. Why? Because milk is the perfect host for growing an assortment of bacteria, yeast, and molds due to the sugars and nutrients it contains. Sometimes we want these things to grow (as in the cultures that we intentionally add to milk when making cheese), and sometimes we don’t. In addition, the conditions under which most cheese is made — warmth and humidity — makes for the exact environment that many contaminants thrive in.
Not to scare you off from making your own cheese at home, but in addition to listeria prevention, we want to avoid other nasty bugs including E. coli, salmonella, Clostridium botulinum, and campylobacter. Heady stuff and enough to make you wonder if it’s worth the risk? I say, whole-heartedly, yes! But take steps to ensure your homemade cheese is the safest it can be.
First, let’s look at how contaminants can get in your cheese in the first place. Many of these microorganisms naturally occur in the world, just waiting to find a place to grow and thrive. There can be several points of entry into your cheese. The milk itself could be contaminated, the cheesemaking equipment could contain residues from improper cleaning, or the environment (including the kitchen counter, your hands, your aging space, etc.) could be the culprit. So, with all potential contaminants including listeria, prevention is your best defense.
The two places it is most important to focus your attention when addressing listeria prevention are the milk and the environment. Let’s start with milk quality:
1. Raw vs. Pasteurized: When milk comes out of the animal, it is raw. For centuries that’s how people drank milk. Usually that went well, but sometimes it didn’t. Especially when people moved to cities and the animals they milked were in crowded, unsanitary situations that led to outbreaks of foodborne illnesses and deaths. Pasteurization — heating milk to a certain temperature for a certain amount of time — was a real lifesaver because it killed most of the pathogens that made people sick. Pasteurization can be an important step to listeria prevention. But it also kills a lot of good stuff (think probiotics) and it can damage the milk structure, so now many people are trying to get raw milk back in their diets. We don’t have time or space to address this issue in detail here, as it’s quite complicated and somewhat controversial. But there are pros and cons to working with raw milk, so make sure you fully understand both the risks and benefits.
The FDA has specific rules for the use of raw milk in cheeses made in regulated creameries. One of those is the 60-day rule, which says that any cheese made with raw milk needs to age for at least 60 days. Home cheesemakers are encouraged to follow these same guidelines. Many do, and many don’t. But it is easy to learn how to pasteurize milk.
The rule was intended for harder, drier cheeses — the ones we typically age for a while. These cheeses have a lower moisture content and so the possibility of listeria and other pathogens surviving and thriving is lower. However, sometimes cheesemakers make soft, high-moisture cheeses with raw milk, then try to make them compliant with the 60-day rule by waiting longer to consume them. This practice creates conditions exactly right for those bad bugs to thrive.
2. Farm-fresh vs. Store-bought: Milk that is commercially available undergoes a lot of testing and the producers have to follow strict regulations, which helps with listeria prevention. This doesn’t guarantee safety, as we have all heard of problems that occurred even in regulated facilities, and often with foods other than dairy products. But at least there are standards, and for the most part, this works pretty well.
If you choose to use raw milk for cheesemaking, chances are you’re getting it directly from the farm (unless you live in a state where you can get it at the grocery store). As much as is possible, it’s important to know how that milk is handled as well as the health of the animals it came from. If the animals are your own, you have a lot of control over this. If you’re getting your milk from another farm or producer, ask some questions. What type of testing is done on the animals? For instance, I do a mastitis test on my does every week so I can catch problems early if they should occur. What kind of testing is done on the milk itself, and how often? There are labs that do a full raw milk panel to let you know if you have any alarming contaminants which you may not have known about. It’s wise to do this testing at least once a month. How is milk handled in the milk house? After milking, the milk should be rapidly cooled as quickly as possible, and if making cheese from it, should be used as fresh as possible.
3. Milk Storage and Handling: Because warm milk creates conditions perfect for microorganisms to grow exponentially, it’s crucial that milk be kept as cold as possible until ready for your cheesemaking. A temperature of 40 degrees F or lower is necessary to keep milk safe. When it comes to listeria prevention, this will not be enough, as listeria can thrive at even cold temperatures. But it’s still important to keep milk cold to avoid other potential problems.
Another consideration if you use the milk from your own animals is that your milking equipment and storage containers need to be clean and sterile. It does you no good to have a healthy animal providing good, clean milk if you just go and put that milk into a dirty container.
CLEAN, CLEAN, CLEAN!
1. Clean and Sanitize: Clean milk is important, but a clean environment is just as important, if not more. Make sure all your equipment is clean. Remember, you can’t sanitize something that isn’t clean. These are the basic steps to proper cleaning:
- Rinse in cold water first.
- Wash to remove food and other residues.
- Rinse again.
- If needed, use vinegar or another acid wash to remove milk buildup, also known as milk stone.
Once everything is clean, it can be sanitized. There are several ways you can do this:
- Put everything in hot water and pasteurize it (145 degrees for 30 minutes or 161 degrees for 30 seconds); or
- Soak everything in a bleach solution (one tbsp bleach in one gallon of water); or
- Use a dairy-safe sanitizer such as StarSan (follow label instructions); or
- If using an automatic dishwasher, set it on the sanitize setting.
2. Target Food Safety with Zones: It’s usually obvious that anything coming in contact with the milk and cheese needs to be clean and sanitized. But sometimes it’s easy to forget the areas outside the actual pot of milk that are just as important to avoid other types of cross-contamination. Here’s a quick overview to help you be aware of other places where food safety can be compromised:
Zone 1 — Food contact zone.
- Hands, utensils, pots, counters, cheesecloth, forms, etc.
- Use paper towels or freshly cleaned and sanitized tea towels to dry.
Zone 2 — Areas of possible contamination near your cheesemaking space.
- Sink, refrigerator handle, faucet, cell phone, water glass, computer.
Zone 3 — Areas of possible contamination further away from your cheesemaking space.
- Door handles, outdoors, barnyard, animals, etc.
For a more in-depth look at food safety in cheesemaking, here are some good resources:
Originally published in the May/June 2019 issue of Goat Journal and regularly vetted for accuracy.