Hazelnut spread preservation

Question

I'm making some hazelnut spread at home and trying to preserve it as long as possible. Basically, I blended a mixture of ground roasted hazelnuts, skimmed milk powder, sugar, cocoa powder and very little amount of hot water in food processor. I then added melted vegetable shortening and lecithin in the mixture and blended until it has a nice texture and spreadability. It was kept in a sterilised glass jar.

I was hoping the finished product might last a few months before it turns bad, however, there were some bacteria/mold/fungus on the surface only after about three-four weeks.

My questions are 1.) what causes the bacteria growth (is it caused by the water/moisture level) ? 2.) what other substitutes for hot water (to dissolve the powder mixture)?

Thanks in advance guys :)

Answer 1

what causes the bacteria growth (is it caused by the water/moisture level) ?

Each of these foods on their own are preserved by having too little moisture for bacteria or molds to live in. So in your specific case, it was likely the water which made it hospitable for them again, yes.

If you have a food which supports bacterial growth, you cannot make it safe by simple sterilization. The sterilization is not always sufficient, and you need laboratory tests of your recipe to confirm that it can work with sterilization (usually only OK for some combination of sufficient acidity and sufficient processing temperature, like water bath canning). And it is no longer shelf-stable after opening. So I wouldn't suggest going down that road. Sterilization of the jar doesn't matter.

You can try making any gianduja recipe that doesn't call for water-containing ingredients (butter or cream or water). There is no need to pick one with cocoa powder or milk powder. Or if you are very intent on using the powder, melt the sugar as for caramel (waterless method) but stop as early as possible, before you have gotten much caramel flavor. Add the powders to the caramel and mix thoroughly. Adding the shortening at the same time can make it easier.

The problem with this approach is that you can have difficulty making it spreadable, since the water thins it. But maybe it will work with enough shortening added.

As for botulism, I have not heard of gianduja being a botulism risk, but homemade variants usually require refrigeration, so you may want to research that separately.

Answer 2

You put it in a sterilised jar but it doesn't sound like you even pasteurised it before it went in (or presumably use sterilised tools). So that's probably how it got contaminated; trace levels of mould spores are everywhere. Even if you did pasteurise it you should worry about botulism (see many questions/answers here).

Personally I'd try making a small batch and eating it up quickly, but put some in the freezer in a suitable container to see what happens. If it freezes OK, then pack up the next batch in small quantities and freeze, defrosting as required. You may extend the keeping time in the fridge, but it may be useless at fridge temperatures.

Mixing the powders into the hot fat might help it keep better, if not for mould formation than for separating (depending on how much lecithin you used). Cocoa doesn't dissolve in water, neither do all the constituents of milk powder, so you were only dispersing them in your last attempt.

This will probably only ever have a short shelf life at a temperature at which it's spreadable.