Chocolate – What’s the recommended temperature for chocolate to set

I don't know the details of this particular recipe, so you'll have to excuse me if this comes across as a bit of a shot in the dark, but here are a few things that could have gone wrong:

• Grainy chocolate is usually a sign of seizing. White chocolate still contains cocoa butter and can still seize. Therefore it's important not to let any liquid touch the melting chocolate and to not let the temperature get too high.

• 130-140° F is definitely way too high. White chocolate will normally burn or seize at temperatures higher than around 110° F. You mentioned that the second time you used the right temperature, but it's worth pointing out anyway: Be very careful with the temperature, don't use direct heat preferably, use a double boiler or a stainless steel bowl placed over a steaming pot, and stir frequently to keep the temperature even.

• Don't dump hot cream into the chocolate. It's strange that almost every recipe tells you to do this; water causes melted chocolate to seize, period. The only way to avoid this is to use a very large amount of liquid for a very small amount of chocolate, so what you have to do is go the other way; incorporate the chocolate into the cream, a small amount at a time. This is especially important with tempered chocolate because you've essentially raised the melting point!

• Also be careful not to let any water get into the chocolate as it's melting; use dry utensils and make sure you don't have any steam condensing over top (use a large bowl over a small pot if you don't have a double boiler).

• Finally, as Joe commented, make sure you're using the right kind of white chocolate. I've never seen baker's white chocolate, so when I need white chocolate for melting I generally use the white chocolate chips. If yours didn't burn at temperatures as high as 130° F then you might have been using coating chocolate instead.

Follow all those precautions and you should end up with a very smooth mixture. I've done this for ganaches and even foams and it's never a problem if you're careful about both the temperature and moisture.

I'm going to blame your thermometers.

The one you used for your first batch you believe was a bad one, so it likely was measuring the temperature incorrectly, so you got poor results.

Then, you bought a really fancy infrared thermometer... which is great for measuring surface temperature but is pretty useless for anything else. Note that surface temp is usually much different than internal temp. Generally, if you're heating something up, the surface will be hotter than the inside and if you're cooling something down, the surface will be cooler than the inside.

This means that all your temperature readings were wrong!

Here's some info about the internal temperature reading myth:

2. An infrared thermometer will tell you the internal temperature

This is another myth worth busting. An infrared thermometer is a surface temperature tool – period. If you’re grilling, baking, smoking, or roasting you’re going to need a penetration probe to tell you the internal temperature of the food you’re cooking. An infrared will only give you the surface temperature of the food, and depending on your optical range, the temp of the surrounding grill, skillet, oven, etc.

I think you should try your chocolate tempering again but with a good-quality instant read thermometer (make sure the temperature range goes low enough) or a candy thermometer (again, some of them start at 100 F, so make sure it goes to the temps you need).