I remember reading somewhere that there are time/temperature plots for thermal death rates of various organisms on cocoa beans, but I can't find it now.  Can anyone point me in the direction of these?

Asking because I'm switching my roasting from sheet pans in a convection oven to a drum roaster that will allow the introduction of steam (not superheated though, just adding water to a very hot oven). and I'm looking for a baseline for 1) how long to expose beans to steam for effective thermal death, and 2) if i don't use steam what time and temp to expose the beans for a log 5 kill. I'll be roasting 60 lbs of beans at a time.

I know there are lots of variable to consider, so am looking for general direction at this point.

Thanks in advance!

Mike

Sounds like you're doing a lot of the right things.  If you've not already done so, i'd encourage you to undertake a validation program to assess the kill rate of salmonella surrogate organisms (you don't *actually* want to do the test with real salmonella...), as the energies required to kill salmonella to a 5 log kill can look different than those required to reduce yeast by 5 log.  Don't forget your environmental swabs (things like floor drains, for example, become excellent harborage points for salmonella that can be tracked through the facility on one's shoes)..

True sterilization is very difficult - usually due to environmental factors.  Cobalt-60 irradiation is effective, as are some gasses.  Both those options come with serious considerations.

I will agree with you on the fact that total plate counts, yeast and mold are not indicators of coliforms or salmonella presence. 

Guusb above asked about sterilising nibs.

I have been looking at options for sterilisation on the bean processing line we are building. Suppliers strongly suggest installing a sterilisation step in the process as this is very common practice in industrial applications, especially where the the product is sold on to other industrial customers and requires very low TPC results.

In whole bean roasting this is achieved by injection of steam into steriliser before roaster and requires quite large steam generation capacity.

I have looked at results of our micro testing over last few years, and TPC on beans range from 3x10^2 to 4-5x10^6, in cocoa liquor we have never gone over 8x10^3 and most results are below 1x10^3. Australian standards for finished chocolate require less than 1x10^4 and we have never had finished product at more than half of this level.

We are not selling any product to other industrial customers and looking at low probability of large salmonella contamination on beans and even lower chance of this contamination surviving roasting and grinding process we have decided not to install any additional sterilisation steps in our process.

I have left a space for this just in case things change.

Lot of good questions in there that can't be answered briefly.  Short version is you need to be most concerned with achieving an effective 4-5log kill on Salmonella - the danger lies in ingesting viable organisms that can then multiply inside you.  All treatments you mention (steam, nib, bean roasting) can be validated to safely achieve the necessary level of kill, although they all work slightly different from one another, and the settings you use to get a 5log kill on one method will likely require you to modify them for another.  Post roast-contamination should always be part of your flow design - you don't want to effectively roast the beans only to re-contaminate them when you remove them from the roaster (it happens).  Steam is a MUCH more effective way of killing micro-organisms than straight dry heat, as the energy associated with heating water is greater than the energy associated with heating air to the exact same temperature.  It is that energy, then, that results in the death of your micro-organisms.

Thanks you, Peter3 and Sebastian! You both have a good points. It is always a good idear to do addional lab tests. I'll devinitely look in to that. 

Sebastian, am I right in thinking that the roasting proces will kill coli and salmonella, but seen as they are both have endotoxins, a death large enough colony is still a hazard? With this in mind, is bean roasting not more hygienic than nib roasting, so live bacteria can migrate from shell to nib? (Can nibs be contaminated when the shell of the bean is intact?) What is the addion of steam sterilization? Is steam sterilization only necessary when the bean-breaking step is done with unroasted beans? 

I'd strongly disagree with that.  TPC, yeast, and mold are more indicators of storage/transport conditions (ie did the materials get wet at some point) and general quality, but have very little to do with organisms of public health concern.  Coliforms and salmonella sp. are *the* reasons for kill steps in chocolate making processes, and as such are the organisms of concern to be targeted for enumeration.  It is those that one needs to concern themselves with.

Steam sterilization of nibs in commercial roasting operations is not an uncommon thing to do.

Use nibs from your current process to make cocoa mass.

Find a local micro lab (there are plenty of them) and get the cocoa mass tested for total plate count, yeasts and moulds.

While you are waiting for results find out what is your local micro standard for total plate counts in chocolate products.

Get the results from the lab, compare to standard and you will know if you need to change anything.

If in doubt come back here with results.

Whole thing will cost you less than 100 Euro.

Most probably you will find that you don't need to do anything.

Hello everyone, 

A question concerning hygiene here for a small bean-to-bar chocolate production in Europe.

To maintain a good flavor I  roast whole cocoa beans. I roast in an oven. Ofcourse after the bean roasting comes the breaking and winnowing. I wonder if its good the sterilise the nibs (with steam) after winnowing en before grinding them. The most hygienic way would be break-winnowing-steam-roast. I have tried to oven roast nibs but it is difficult not to burn the nibs.  

Does anyone have any suggestions?