Cross-Contamination: Keeping Your Cultures Safe from Each Other


Cross-contamination is the transfer of microorganisms that are naturally found in food from one food to another. This can easily happen when making cheese, lacto-fermenting foods, or keeping a methodical culture such as kefir or kombucha in your kitchen.

Cross-contamination can give rise to a variety of problem. Serious cross-contamination, which can come from raw meat juices or harmful, flourishing bacteria getting into a raw fermented food, can make you very sick. Common cross-contamination, like two different species of good bacteria (such as kefir and sourdough cultures) coming in contact with one another, will just cause frustrating problems and will often cause your ferment to be altogether unsuccessful.

The term cross-contamination can also refer to the problems caused by dirty hands, countertops, jars, and utensils. This is why you are constantly reminded in cheesemaking, culturing, and fermenting instructions to maintain a clean and healthy workspace. That way you bar the path for any harmful bacterial action which might result in bad smells, tastes, and looks, and all-around food fermentation failure.

How Cross-Contamination Happens
and Steps You Can Take to Prevent It

Cross contamination can happen in any kitchen, whether you keep a neat and tidy kitchen as a rule, or you are rushed and busy and the kitchen gets dirty while you aren’t looking. Attention must be paid no matter how clean your kitchen is. Common problems that result in cross contamination are:

  • Improperly cleaned jars used for fermenting or culturing dairy, vegetables, fruit, or kombucha.
  • Unclean hands used for chopping or stuffing jars with fruit or vegetables to be fermented.
  • Wooden utensils retaining bacteria from earlier projects. Since we use wooden utensils a lot during our food fermenting projects, this can be a problem as wooden utensils require a more scrupulous cleaning than plastic or metal utensils do.
  • Any unclean or improperly washed utensils.
  • Keeping two different types of culturing or fermenting foods too close together during the fermentation period, causing airborne cross-contamination. (For instance, keeping a working milk kefir jar too close to a live sourdough or yogurt jar.)
  • Keeping fermenting projects too close to any source of ambient bacteria, such as trash can, sink drain, compost container, open loaves of bread, air fresheners, etc.

Here are some tips and easy steps you can take to prevent cross-contamination in your kitchen:

  • Separate meats from foods that are eaten raw, such as produce, in your grocery cart, at the checkout, and in your refrigerator.
  • Don’t scrub vegetables or fruit before beginning a culture or ferment in an effort to avoid cross-contamination. This will remove the naturally present good bacteria which are necessary for a successful, tasty ferment. Rather, rinse them gently in cold water.
  • Keep fruits and vegetables to be fermented or culture chilled before you use them, if you can.
  • Keep your culturing foods away from each other. They will be okay if they are the same thing, like two jars of sauerkraut, for they both have the same species of bacteria working within them. But foods like kefir and kombucha, sourdough and piima, or yogurt and sauerkraut do not need to sit near each other. Four feet apart should keep them sufficiently to themselves.
  • Keep your tools and workspace clean, and rinse everything with plain water to remove any soap or chemical cleaner residue.
  • Don’t allow pets in your kitchen while you are making cheese or starting a culture or ferment.
  • Keep countertops free of clutter and things that can be easily spilled.
  • Don’t wear perfumes or fragranced lotions when making cheese or culturing food, and if you wash your hands with soap, fragranced or otherwise, rinse them well. Roll up your sleeves, too.
  • If you will be doing multiple culturing projects, make sure to clean your workspace thoroughly after each one so as to eliminate any lingering bacteria or flavors or smells.

These steps will help to avoid cross-contamination in any culturing, fermenting, or cheesemaking venture. You will be one step closer to a successful, happy, and healthy food culturing experience!



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