Ask the Alchemist #53

I have become interested in home chocolate making (with the possibility of selling one day) and have been slowly learning about the process and acquiring equipment. However, I have some concerns after seeing posts on your forums and elsewhere about pathogens (salmonella, e. coli, etc) in unroasted beans. It sounds like roasting is really the one and only kill step in the chocolate making process. However, there are some people who suggest that, if present, salmonella and e coli may be able to survive roasting. To address these issues, it seems that you could take the following actions:

1. Purchase beans from a source that you can trust, keep equipment clean, use good manufacturing practices to avoid cross contamination

2. VERIFY that a particular roasting profile reduces pathogen counts to acceptable levels (this will depend on bean characteristics, roast time, temperature, roasting technique, etc)

3. Spot check pathogen levels in the final product

Item 1 is well within the capability of a home or small production chocolate maker. However, items 2 and 3 would require some lever of expertise, lab testing, and money that may be beyond the reach of a small scale chocolate maker. Is there a way to quantify the effectiveness of the roasting step for home production? Is there anything that a small chocolate shop can do to provide some confidence that the final product is safe?

Thanks for your input,


This is something I’ve touched on before, and it is worth addressing again. Yes, in theory, salmonella and e.coli could survive some roast treatments, especially if you view the temperature vs time kill curves for wet and dry media for these contaminants. But that is theory to my knowledge. In practice, I have not ever see a roast not kill e.coli or a much more heat resilient spore. If I had to surmise why, I think it might have to do with the nature of how I roasted and how that differs from how the kill curve data were collected. Please keep in mind this is just a hypothesis based on my observations.

Labs where these kill curves are produced use either ovens or autoclaves. In both cases they are filled with test media, and are pretty static environments. They might have some air circulation, but the items themselves never move. They are testing for worst case scenarios. And the e.coli is inside a liquid or wet media. In roasting (for my test) the beans were heated in a roasting drum, with a significant temperature gradient, lots of convection and a very thin layer (the husk) that had to be heated for decontamination to occur. Mostly bean movement, the convection and thin layer are the reasons I surmise roasting works.

That said, I should clarify that static pan roasting in an oven may not do the trick, especially if the beans are at all stacked up. That’s worth considering when you roast.

As for your points, let’s just tick them off.

Agreed. Source is important. And avoiding cross contamination is paramount. It is very often overlooked. Do you have dedicated bowls and buckets for raw and roasted beans? You need to.

1.  This is something that each person can do, but not something I or any supplier can do for you. As surmised above, the roasting method can possibly radically affect how effective a given roasting profile is. And related to point 3) I would not go to this level unless you have positive results in your finished product.

2.  Agreed. This is good to do, and if you are in production, I think the peace of mind way outweighs the cost. And if you look into it, I don’t think you will find testing is all that expensive. Sure, maybe for the home chocolate maker it is (which is why 1 is important) but not for the one doing it for business. Less than $100 I’ve seen. It is also worth keeping in mind that final product testing is more likely to pick up contamination as it will have been more evenly distributed through the product. I find spot checking 10 beans out of a 2 lb roast not greatly comforting.

3.  So what can you do at home? Well, the only true way to be very sure is to test. Everything else is just precaution. But if you do, don’t get lulled into a false sense of security by doing one final product test with a clean result. If your beans were clean to start with, there is no reason to expect the chocolate not to be clean. You pretty much have to run a control where you contaminate your beans and run them through your whole process (making sure you clean well afterwards just in case).

That all said, sadly, I have to say no. There is no easy, cheap, reliable method to test whether your chocolate is safe. Life is full of uncertainty and some amount of risk. And in the scheme of things, making chocolate is not one of them. Sure, it can be an issue, but the few cases of product contamination have always come down to a breakdown in some procedure that is in place. A faulty temperature sensor. Cross contamination. Post contamination. In that in nearly a decade I’ve not heard of one single case of someone getting sick from chocolate they made or that was made in small scale says something. Sure, it too is a minor false sense of security, but there is something to be said for vast pools of no positive data. Generally, I know, it is bad practice to try and prove something by the lack of evidence (which is what I am saying) but at the end of the day, if that is what you have, it is what you have to go with. And you must keep in mind no one (to my knowledge) says roasting 100% kills pathogens. I’ve been VERY clear about that. But I have reported that when I actually tested basic roasting profiles with contaminated beans valid data was produced (sample set of about 24) that no live pathogens were found afterwards.

So we are not totally working in evidence vacuum after all. There is data that drum roasting profiles are effective and so far, there is no evidence to the contrary.

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