I used to be wary of making mayonnaise, but with the Thermomix I have never had a fail ... big call I know, but if you stick with some basic principles you could do this too.
These are the "rules" that I work with in making mayo:
1. I use a "light" olive oil ... the first time I used extra virgin olive oil I couldn't eat the mayo ... and I couldn't "save" it either! It was such a disappointment and a waste! The mayo was too "burnt" tasting which I later found out was to do with the oil working in combination with the yolk (it's a "science thing" to do with emulsifying), so now I stick with a light olive oil (and this is the same oil I use when baking as I can't use nut oils due to allergy in the family)
2. Use the freshest free range egg (organic if possible) you can get your hands on ... the general rule of thumb for how long your mayo will keep is the "use by" date of your egg ... make a note of that date on your container and that will give you a guide as to how long your mayo will last (in the fridge) ... I usually get 4 weeks from my mayo, but we normally use it well within that time
3. You can't successfully freeze mayo ... if you do it will split when defrosted ... it won't be "off" to eat, but it won't be lovely and thick either ... you can still use it to make a thin sauce as the flavour will be there, but it won't be any good for dressing salads
4. I only use the yolk and not the white (you can use both if you wish and that is known as 'whole egg' mayonnaise) ... I freeze the white to use in baked dishes, and it means by organic $ goes further and that makes me very happy ... you can freeze them in ice-cube trays knowing that each cube is an egg white, or in general ⅛th cup (or roughly 35g) is equivalent to 1 egg white
5. Use vinegar instead of lemon juice as an acid ... I love lemon juice, but the acid content of lemons can vary from variety to variety, and from season to season ... you need the acid to help "set and thicken" the egg yolk, so by using a vinegar (any vinegar you like, but I generally use white wine vinegar or apple cider vinegar) you are going to get a consistent result
6. Weigh your oil into a container using the Thermomix scales (either place jug on lid or remove ™ bowl and place jug on carousel) so that you get the right amount needed for the recipe (don't assume a cup measure - which is 250ml - is the amount needed as oil has more volume than that ... see picture in post to note what I mean)
7. Have everything at room temperature before you start, and
8. Always use your butterfly - I know there are many recipes for making mayo, some without using the butterfly, but again I have never had a "fail" when using it ... if you are unsure of where to place your butterfly check the pics ... note that the butterfly sits to the LEFT of the single blade that rises up from the shaft (three blades go down towards base of the shaft and one comes up) ... if you put the butterfly in that position it will hold in place and not fly off