Ask the Alchemist #144


I am using a sous vide cooker to regulate my temps but I have yet to be able to temper a chocolate (55% dark milk) without the same problem this gentleman photographed in his chocolate. Small dark dots clustered together.

http://seattlefoodgeek.com/2010/12/the-strange-effects-of-tempering-chocolate-with-a-sous-vide-machine/

I tried three different routines in my sous vide for tempering. All with temps going from 119 degrees to 81 to 87-90. Tried with constant mixing by hand on bag with short soak time (5 minutes at each stage), constant mixing with long time soaking between temps (20 minutes at each stage), and no mixing with long soaks (30 minutes at each stage). All the chocolate looks like in the link above. The funny thing is when I was done filling molds (all perfectly dry at room temperature and 25% humidity room) I took the extra and put in one of those solo cups and that chocolate had the least of the black spots.

I am at a loss. Not sure what could be going wrong. Any idea? I am experimenting with various levels of mixing and various soak times at each temperature but still getting the same effect.

It funny. I love the idea and tech of a sous vide. And there are some amazing looking circulating immersion heater that I think would allow you to make your own version of the EZTemper, ala water bath. But the same thing that makes it great for that application is (I think) the same item that is causing grief with tempering.

In short, kneading or no kneading, it is really hard to get an even distribution of thick material inside a bag. If you don’t believe me, try taking a cup of shortening (butter is ok but what a waste) put it In a bag, put a drop of food coloring in it, and then try and knead the color in evenly. Maybe you can do it, but I bet you end up using your eyes a lot. Working the areas that are uneven, etc. Doing it with your eyes closed you will end up with a whole bunch of rather attractive swirls I’m willing to wager.

The issue is that even though the water surrounding bag of chocolate is an even temperature, there is just no way that the chocolate is that temperature, 100% homogeneous, in the short amount of time you are giving it. That is the first thing that struck me with Scott the Seattle food geek. He was not kneading or mixing at all. It seemed to me he was expecting the system to become homogeneous nearly instantly. He mentioned holding the chocolate at a temperature for 2 minutes. Maybe, just maybe the temperature was even throughout the chocolate. I say it was for the sake of argument (I don’t believe it for an instant). What absolutely was not even throughout was the distribution of Type V crystals.

And that right there is the crux of the entire issue. See if you can follow.

We use temperature as a way to determine if the chocolate seed is evenly distributed because we are mixing chocolate of different temperature. We are stirring the entire time. When the temperature is the same throughout, we can be confident we have distributed the seed evenly. The key here is that what is important is the distribution, NOT the temperature. The temperature is just what me measure.

Now, to be clear, temperatures ARE important. The seed will be destroyed if it gets too hot. I’m just saying it isn’t the only thing that is important.

Wen I was In the lab, and we were mixing up water solutions, the rule of thumb was to invert and swirl them 10 times. That is a lot of mixing. Stirring with a stir plate often took 10 minutes. It too that long for particles to REALLY distribute well. Heck, it is why sous vide circulate. And why what is in that sealed bag in the sous vide can’t be even in 2 minutes – there is no circulation in the bag. If anything, it is inhibiting circulation.

To make a sous vide work for temperature I suspect you would need to hold each temperature for 60-120 minutes to be sure, hand kneading 6-8 times throughout. That seems like a lot of work for something that is supposed to be saving you work.

I want to swing back to both the referenced article and your own experience. In both cases the lower temperatures were the goal. He took his chocolate (in theory) to 84 F. You took yours to 81 F. His was clearly too warm and seed did not form. In your case, it may or may not have formed. But you ‘sin’ was that the temperature was your goal. And that is wrong. The goal is cooling until the chocolate starts to thicken. That is the indicator you are looking for that seed is formed. And for all I know, you did take it to that point and are just reporting the temperature.

The next problem is that he took it to 88 F for only 2 minutes with no mixing. The temperature (if it was true which I can’t believe with a 2 minute hold) is fine, but the lack of mixing means the seed (if it had been formed, which it was not) would not have been distributed evenly.

In your case you took it to 87-90. You pretty much have a no win situation. At 87, even with mixing (remember the colored shortening?) you most likely had cold spots where Type IV crystal were hanging out. Those lead to those spots you see. At 90, since this is milk chocolate, you are way too hot. So you had areas where no seed or crystals of any type existed. Hence the swirls and other spots.

In short, it looks to me you probably didn’t form seed. If you did form it, you either didn’t distribute it well, and/or had hot and cold spots because chocolate is thick compared to water and is damn hard to mix in a bag (corners are brutal).

How can you make it work? I’m honestly not sure. I’ve known a few people to get it to work and generally they take the slow approach. Each stage is 2-3 hours with periodic hand mixing.

At the end of the day, ‘fast sous vide’ which is what you are attempting is sort of an oxymoron. It’s just the wrong tool for the job in my mind.

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