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Cold brew coffee is keeping me awake… and it’s not the caffeine.

One of the most fascinating peculiarities about food geeks is that we are very creative. It when you have a good idea, it’s hard to hold it back. Food safety, however, sometimes may get in the way. If you have a new food that is extremely popular, both industry and consumers love it, it’s not easy to stand in the way. In some cases, the food safety issue is a very small risk of something really bad happening, and this may not sound alarming enough to convince consumers and manufacturers to pause, or maybe even regulatory authorities to act.

Cold brew coffee is one of the simplest foods you could possibly make, and full disclosure: it’s awesome and it’s becoming ever more popular. One cup of ground coffee, two or three cups of water (yeah, the stuff is really strong); steep in the fridge for 18 hours; filter it, enjoy. In terms of food safety, there is not a lot to be concerned at this point. You start with the ground beans (which were toasted, pretty much sterile) and water (luckily, most of us – still – have great water right in our faucets) which should both have very small contamination levels. You may want to boil the water if you are using a well and can’t really vouch for your filtration system. However, after the two ingredients are mixed together, any contamination will have a chance to grow if it can get in the mixture, survive the inhibitory compounds present in coffee and grow using the limited resources available and at low temperature. Unlikely? Well, never underestimate our microscopy companions. The cold never bothered Listeria monocytogenes, for instance. And we know hot brewed coffee has indeed some inhibitory compounds, but at least some lactic acid bacteria (which are not pathogens, most of them are seen as beneficial to us) can survive in that environment. It may be that pathogens will not survive and grow. The worst-case scenario at this point would be that we may need to be extra-vigilant about the good manufacturing practices (to prevent contamination) and make sure the cold brew coffee is kept refrigerated and consumed within a relatively short amount of time.

But, did I mention foodies are extremely creative?

Enter nitrogen. Different from Oxygen, Nitrogen gas (N2) is very stable. As a result, removing the air from the package and adding nitrogen already brings the benefit of slowing down the oxidation reactions that damage the delicate flavors in the coffee, a change even more noticeable in the cold brewed. But this is not the only reason why Nitrogen is added to some beers when you open the can: it turns out that, for thermodynamic reasons (a fancy way of saying I couldn’t understand it), Nitrogen makes much smaller bubbles in water solutions. The smaller bubbles take longer to separate and break down, which gives the beverage an exquisite creamy mouth feel. And there it is,  after millennia after the first human being decided to roast those beautiful little fruits our civilization has finally decrypted the code for the perfect beverage. Who am I to stand in front of such accomplishment?

Problem is that it’s not me. It’s them

Once we remove the oxygen from the package we created an environment where anaerobic bacteria, otherwise incapable of dealing with the oxidation reactions carried out by oxygen, are able to grow. I must say: luckily for us. Most of these bugs grow very slowly, are very sensitive to everything and just can’t compete for food. Still, we haven’t had a chance to be exposed to them enough to develop resistance to their tricks, and, as a result, many can cause us harm. In fact, the list of anaerobic pathogenic bacteria includes one of the most dangerous food-borne pathogens, Clostridium botulinum. You probably have heard of botulism. It’s horrible. My 9-year-old son tells me that it takes only 2.5 nanograms of botulin, the toxin produced by C. botulinum, to kill a person, and one cup could be enough to wipe out the population of the Americas. It must be true, he learned that at school.

So, am I saying that you could have died a horrible death for drinking nitro-cold brew coffee? Not so simple. C. botulinum is not (again, luckily for us) as widespread as it could be, so it probably wasn’t present in the product to begin with. And if a few spores were present they wouldn’t have been able to germinate and grow at low temperature. And yet, even if that keg of delicious cold brewed coffee was left in a hot truck for the whole day, we don’t know if they wouldn’t have been able to germinate, grow and produce the toxin. There is a possibility, however, that they would be able to do just so. Important to know too, if there were any risks of botulism in this case, they would be much higher if the product was deliberately stored at room temperature. The risk is also higher – and this may sound counter-intuitive to some – if the product is pasteurized after packaged.

The important  message to be conveyed is that there is no scientific information that shows cold brew coffee is safe when kept in a reduced oxygen packaging system, such as nitrogen-infused cans. Granted, this is not the same as saying we will never learn a way to make it safe, but in doubt we must wait until we can be sure. We don’t take any risks with Clostridium botulinum.We are working on preliminary studies that will shed some light on this issue, but it may not provide the final answer that we need. And I, for one, will sadly hold on to my desire to have a refreshing bubbly coffee after lunch. Luckily, summer is over (whatever that means these days…) and a warm bulletproof coffee at 3 o’clock is not a bad idea. Join me?

29 thoughts on “Cold brew coffee is keeping me awake… and it’s not the caffeine.

  1. Thank you very much for writing this article, especially in light of the recent cold brew scare! Please publish this in ALL social media so that more people, especially the younger crowd, learns about it! Much appreciated!
    Karen

  2. Has there been a challenge study to see if C bot would grow under those conditions ( canned with N2)? Is what were the results of the study? There seems to be a lot of cold brew on the shelf these days. How safe is it?

    1. We do not know of a successful challenge study for C. bot in Cold Brew Coffee. As far as we know, there isn’t a validated process for shelf stable Cold Brew Coffee except for retorting. Because of the lack of information we would not assume that shelf stable cold brew coffee is safe. Best wishes, Bruno.

      1. Update: I ran across this patent which describes a – successful – challenge study with C. botulinum inoculated into very concentrated cold brew coffee.

  3. can’t you just add citric acid to coffee to get the ph low enough, isn’t it true that botulism can’t be produced in low ph?

    1. Hello Brent. You are totally right. At a pH of 4.6 or below C. botulinum cannot produce the toxin. Adding an acid to lower the pH would help with that issue and possibly leave only Listeria as a food safety hazard. However, the acidification changes the taste of the product a lot. Maybe it would be an even more refreshing option for the summer!

    1. One important aspect of the physiology of Clostridium botulinum is that it is a very weak competitor. If you eliminate the competition (by pasteurization – which does not eliminate the C. bot spores) you are actually helping them have a better chance to grow and produce toxins. This also explains one of the strategies that have been used to make these products safer: addition a healthy microbial competitor (such as lactic acid probiotic bacteria) which are also referred to as a “protective cultures”. Obviously this strategy only applies to products that are pasteurized before packaging, so the canning step must be done in a clean, pathogen-free environment (environmental monitoring for Listeria).

      1. Do you know of research where lactobacillus or pediococcus was added to out compete clostridium botulinum in coffee or a similar low oxygen low nutrient enviornment?

        1. Yes, we have done that ourselves for many products, you do need to test it, since different coffee varieties, concentration, roasting conditions can lead to different behavior of the cultures over time. Please contact us directly at cfvc@cornell.edu if you would like to evaluate your product.

  4. What advice would you give to current home-brewers (there are many), aspiring to introduce N2, using mini growlers and N2 cartridges to infuse product and keep consistently @32°F for no more than 2 weeks? I would not want to be the cause of an epidemic…

    1. NY State Inspectors allow those kegs as long as they are sold for immediate consumption only and product is discarded if not consumed within 24 h of manufacturing. Beyond that you will need a process review from a Processing Authority. We would then require strict cGMPs and a protective culture, but possibly the process would still need to be validated with a shelf life study. You may want to check with your State inspector for their guidelines.

  5. I have seen a cold brew study where the steeping temperature was done at 21 – 25C for 24 hours. Is that food safe?

  6. Thanks for the write-up! Two questions:

    1) Won’t retort make a shelf stable nitro cold brew?

    2) If you aren’t adding nitrogen, do you still need to retort?

    1. 1. Yes. In any case, a validated retorting process will make it shelf stable.
      2. I’m assuming you are still talking about shelf stable. In this case it may be possible to do it with mild heat, but you would need strong evidence (microbial studies) showing that no changes can occur over the shelf life that would make the product prone to the growth of spore-forming pathogens.

  7. I have been told by a food processing authority that pasteurizing in certain time/temp conditions such as 90 degrees for 10 mins will kill c bot. spores. “pasteurization would eliminate any botulism spores capable of growing below 10 degrees C—it would still require refrigeration. ” This would seemingly extend the shelf life under refrigerated conditions would it not?

    1. Some strains are more sensitive to heat, and may be killed by a 90C/10 mins treatment. These strains are also more easily inhibited by storage under refrigeration. However, this treatment will not eliminate all C. bot strains, and a “second barrier” to prevent toxin production still needs to be introduced.

  8. So for the small coffee shop owner – whose customers are addicted to our cold brew- what is the best path to take? We were about to expand into nitro coffee… But that decision just got changed. However, I hate to stop selling cold brew… If it can be done safely. I am not in New York, and our state does not have any regulatory guidelines. However, I am more interested in my customer’s safety than in obeying the letter of the law.

    1. The best option is to keep product cold and sell retail. I don’t think you should stop selling cold brew, just make sure you are fully considering the hazard analysis relative to your product.

  9. Someone needs to take a refresher course in basic grammar and writing. This is one of the worst writing examples I’ve ever seen in years. Makez your content worthless.

    1. I do, but I don’t think you will be happy with the answer… boiling for 16 hours, for example, will probably do it. 🙂

  10. how is botulism introduced as spores into different drinks? Coffee beans are roasted, so you’d think the beans would at least not be a concern

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