MAYONNAISE MYTHS
Mayonnaise is supposed to have begun as the Spanish allioli, but developed further by the French when they liberated Mallorca and Minorca from the British in the late 1700s.
Fingers of suspicion are frequently pointed at this delicate liaison between oil, egg, and lemon or vinegar whenever foodborne illness has occurred. Yet mayonnaise, on its own, is among the safest of foods. If it is correctly made, mayonnaise is incapable of supporting the growth of bacteria, and causing illness.
Its secret hides in the acidity of either lemon juice or vinegar. The oil is neutral, of course and plays no part in bacterial growth, but all the acid and all the salt is contained in the non-oil ingredients. For this reason, Mayonnaise only supports the growth of bacteria when added to cooked chicken, potatoes, pasta, cold cuts, ham, etc.
A safe pH value for mayonnaise is between 4.10 or 4.00. This can be achieved only if its ratio of egg to vinegar is correct. To make Salmonella-free mayonnaise in the kitchen, at least 20 ml vinegar (assuming 6% w/v acetic acid) per fresh egg yolk, or 40 ml per fresh egg white, or 60 ml per fresh whole egg should be used and the product should be held at 20°C or above for at least 48 h.
{The reason for the difference is that egg yolk has a pH of about 6.7 (very slightly acidic), whole egg a pH of about 8.3 (slightly alkaline) and egg white 9.2 (more alkaline. So it depends upon whether you use whole egg or egg white or yolk).
Conversions: a tablespoon is 15 ml, teaspoon is 5 ml
(Click on the question to reach the answer)
Q: Why is mayonnaise so deadly when mixed in sandwiches and salads?
Q: How long can mayonnaise sit on the table without refrigeration?
Q: The supermarket is selling 'expired' mayonnaise at a reduced price
Q: Why is mayonnaise so deadly when mixed in sandwiches and salads?
A: By itself, mayonnaise is one of the safest foods. Virtually no outbreaks of foodborne illness have been traced to mayonnaise before it was added to other ingredients. Leave it out of the fridge and you may see some separation, or drying at the surface; leave it long enough, and there mat be molds. But once you mix with pasta, potatoes, cold meats, sliced eggs, etc., and the problems begin. Bacteria cannot grow in the original mayonnaise due to the concentrated high acid/salt in the spaces between the oil globules, but with other proteins, fibres, and starches, bacteria find perfect nutriment in which to grow, and for some to produce their toxins.
Q: How long can mayonnaise sit on the table without refrigeration?
A: Theoretically, for weeks, with possibly some drying and cracking on the surface or some separation. But in practical terms, why is it on the table? If it's available to people making sandwiches or mixing into salads? In that case, it's likely to end up with bits and pieces of other foods accidentally mixed in: bits of eggs, olives, shreds of chicken or ham, lumps of potato or macaroni, or bread crumbs... -THAT'S where you can expect bacterial growth. It would be best to bring out a new pot every day.
Q: The supermarket is selling 'expired' mayonnaise at a reduced price
A: The only thing that may occur is that the oils may become slightly oxidized. It's not a health or safety issue, but it produces an objectionable smell and taste. It will happen slowly to any oil- or fat-based food (cookies, dressings, whole-grain cereals, pancake mix, cooking oil), and faster if exposed to abundant oxygen, warmth, and light. So if the mayonnaise has exceeded it's best-before date by a few weeks, it's probably OK, but watch for the taste change.
Q: How to tell when mayonnaise goes bad?
A: I've never known mayonnaise -by itself - to actually "go bad", other than to show signs of rancidity or separation after a long shelf life. Certainly when mixed with other foods (meats, vegetables, starches, herbs, eggs), the composite food can grow all manner of bacteria, both spoilage types and pathogenic types if they are introduced into the mix. This could quickly result in many types of objectionable taste, appearance and odours.