Ask the Alchemist #64

One question that is nagging and I can’t find a definitive answer to, stems from my tempering experiments.

 Does the humidity level of your cooling location affect sugar bloom when cooling tempered chocolate?

After repeatedly finding varying levels of bloom on different pieces of the same batch of chocolate (either swirls of dots, a ‘dusting’ of fine dots or the circular blotches) after two tempering attempts, I tried a test cooling at room temperature and in the fridge. I today read your article on your tests at fridge, room and outside temperatures and noted from the similar results, I’m probably cooling at too high a room temp. (70F+) Next test is with the same room at 50-60F..

I should note that the temper appears reasonably good otherwise, nice snap, reasonable shine, not quickly melting and of course, tastes divine. In some respects my mouth says “so what?” but I’d like to get that perfect finish.

Being in the UK in mid-winter, I imagine a centrally heated house has a lower relative humidity level than that quoted in weather reports. I did note though that in the past day or two when humidity was reported at +90%, the bloom seemed far more prominent than in the first temper a few days back when humidity was lower. If I turn off the heating for that room and keep it closed, I was concerned I may be replacing one cause of bloom (too high a cooling temp) with another (higher levels of humidity).

I do understand that there are many other variables which are in play and I have nagging doubts after reading about moisture in the chocolate or tempering a batch of milk chocolate without lecithin so I realise there may not be a simple answer or I’m just making it harder for myself. I’ll continue to experiment and am about to embark on my first batch from nibs and to try refining another batch from the same base milk chocolate batch but with lecithin to compare the temper.

Sugar bloom seems to be the new ‘hot’ issue. And, somewhat accordingly, not greatly understood. Or maybe more to the point, it is moderately well understood, but that is from a technical standpoint and not a practical standpoint.

Let’s take a step back. What is sugar bloom? First off, what it isn’t. It’s not like cocoa butter or fat ‘bloom’. That form of bloom is the changing of one form (V) of cocoa butter crystal to another (either VI or IV usually). In sugar ‘bloom’, what is actually happening is that sugar on the surface of the chocolate is dissolving, and recrystallizing in a different shape, but with the same type of crystal. But it is still called bloom as it’s similar in appearance to fat bloom. Clear huh?

Let’s get to some background information.

Generally, fat bloom is more common but sugar bloom also occurs and is not necessarily distinguishable from the fat bloom by appearance. In freshly sugar bloomed samples, it is often easy to feel the surface difference; sugar bloom feels dry and does not melt to the touch, while fat bloom feels slick and melts more readily because there are different, lower melting point crystals (type IV). Usually you can see the difference by touching a small droplet of water to the surface. With fat bloom, the droplet simply beads up. With sugar bloom, the droplet will flatten out and spread, as the water dissolves the sugar particles on the surface. Alternatively, gentle warming of the surface (with a hairdryer, for example) will cause the crystals of fat bloom to melt, removing the appearance of bloom, while leaving sugar bloom unchanged.

Next, it’s helpful to know what causes it. Once we know that, we can work out how to fix the issue. These are a few of the not very helpful items you will find about the cause.

1. Storage of chocolates in damp conditions

2. Deposit of "dew" during manufacture from damp cooler air or allowing chocolates to enter a packing room at a temperature below the dew point of that room

3. Use of hygroscopic ingredients (low grade or brown sugars) High-temperature storage conditions of chocolate-covered confectionery, where the centers have a high relative humidity and the water vapor given off is trapped in the wrappings

Personally, I don’t find this really helpful, but that is about all there is out there. The reason is two fold. First, they are just too damn generic. “It hurts when I do this doctor” ”Then don’t do that”. Right!! Let’s get some practical solutions going. Well, before we get there, I need to put in a disclaimer here. We are discussing theory there and this is going to be a 2 (or more) part answer. I’m going to lay out things I think will prevent bloom, and then test them and report back. Following the list:

1. We are talking humidity here. Basically, you need to isolate the chocolate from the ambient water in the atmosphere. That’s either a controlled chiller (that most people don’t have) or getting the chocolate into sealed bags. With a note that refrigerators are notoriously humid. I’ll be testing this by storing chocolate that is setting up in both in and out of a seal zip lock bag in a humid environment.

2. This one is just evil. Dew point. Have you ever seen the equations and multi variable plot for dew point?


Give me a break. And that is the ‘estimation’. Maybe we can do just reference a chart? How’s this lovely?

psychrometric-chart.jpg And that is for one elevation. Not much help there either. Except I think it will help in that I plan to dig in and suss out helpful generalities.

3. I’ll tell you, I don’t believe this one. It sounds good on the surface, but once you have refined, any compounds that are hydroscopic are going to have been bound up. I’ll test it but I’m thinking this one is bunk. That’s a mouthful isn’t it? Basically we can write this one off for our conversation as it doesn’t have anything to do with bars of tempered chocolate. It’s for enrobed items.

Here are a few thought I have about what I will be testing and seeing if they make any difference.

1) Store the tempering chocolate with a desiccant. Lecithin comes to mind. Plus some classics like rice, flour and desiccant packs.

2) I’ll also look at covering each tray with maybe paper towels and maybe wrapping in plastic wrap. The first to ‘catch’ any condensation. The second to seal out any moisture.

3) Finally, I’ll dig into those equations and see if I can find some common, easy to match conditions that will allow you to just temper and not fret.

Stay tuned. This may take some time.