I think the problem is actually not the heating, but the refrigeration!
Consider: bacon fat solidifies easily and thickly, and does so even at room temperature. When you throw it in the fridge, the micro-droplets of bacon fat will turn to solids and clump together. These solid droplets are frozen in place when solid, but when you thaw it, they melt and reveal how wrecked your emulsion is. Now, you could add additional emulsifying agents (lecithin, extra yolks) but that's not really going to solve the problem of refrigeration.
The solution is to break up the bacon fat as it melts, and re-establish the emulsion before it can break. To do this, you have to whisk constantly as you gently heat the mayonnaise, generally in a warm water bath.
How to execute this in a restaurant setting:
Prep a big batch of bacon-mayo and throw it in the fridge. Just before service, warm some water in a pot and throw a cup of the mayo in a small bain marie or metal 6th hotel pan. Immerse the bain/pan in the pot, and whisk it as it melts. Hold the mayonnaise for service in water warm enough to melt bacon fat, and DISCARD THE WARM MAYONNAISE EVERY TWO HOURS AND THAW A FRESH BATCH. Make sure no cooks get lazy about that -- it's a food safety problem. Ideally, you should be using pasteurized eggs to reduce the risk of salmonella. Basically, you're treating your mayonnaise like a Hollandaise or Bearnaise.
I've found that the thawing trick works fairly well for home hollandaise (which most people say shouldn't refrigerate), and which does the same thing if heated fast. It should apply to easily-broken mayonnaise too.
Mayo that splits is typically from one of two things:
- Insufficient water
- Insufficient mixing leading to large droplets
(It's hardly ever insufficient emulsifier, as one yolk can do many cups of mayo.)
The lack of mixing can happen fairly easily with a whisk, but it won't happen if you're using a food processor, blender, or immersion blender.
You're probably normally making mayo that is on the border of insufficient water, so it's fairly easy to get it to break. When you added more water, the emulsion actually became more stable.
That explains why you can't get it to break, I have a few suggestions on how to fix:
- Freeze it. It should break upon thawing.
- If hand-mixed, use an immersion blender on it. That should thicken a little, by better mixing. (Assuming you're not using extra virgin olive oil, which should not be blended)
- I'm sure there are some thickeners that could be added, but I've never tried thickening mayo like this.
Keep in mind that some flavors are fat soluble, some are water soluble, so if you discard part of the water, you may be changing the flavor balance.
Best Answer
Your mayonnaise probably got a little too hot in transit.
Mayonnaise is an emulsion of oil and water. That is, an emulsifier is added to a water-based ingredient that effectively coats droplets of oil and allows those droplets to dissolve into the water instead of coalescing and floating to the surface.
Lecithin is the most common emulsifier used. It is found abundantly in egg yolks.
The emulsion can be damaged if the mayonnaise is heated. When this happens the oil coalesces and you are left with a vinegary base with oil floating on top. Yum.
To fix it you have to reform the emulsion. There are many answers here about how to make or fix homemade mayonnaise. Briefly: You beat an egg yolk well with the water-based portion and then slowly drizzle the oil in while beating like mad until the mayonnaise is thick and white again.
The whole point of making homemade mayo is to use better quality oil and vinegar or incorporate different flavors. It really isn't worth your time trying to save commercial mayo.