Organic Egg Yolk
Egg yolks impart a characteristic delicate flavour on ice cream and have a pronounced effect on improving the body and texture. They improve whipping ability and fat structure, presumably due to lecithin, which acts as a natural emulsifier. It is primarily the lecithin-protein complex from egg yolks that gives them their desirable functional properties (Marshall et al., 2003).
If too much egg yolk is used, fat droplets will become so large that they will be detectable on eating; this is known as ‘buttering’.
I have found ice creams made with egg yolks to be far creamier and smoother than mixes made without egg yolks.
Egg yolks contribute a sweet buttery quality. However, if too much egg yolk is used, this buttery taste can become overwhelming.
Eggs also contribute the distinct hydrogen sulfide (H2S), or ‘eggy’, aroma. This is a very unpleasant flavour in ice cream and is formed at temperatures above 60°C.
Hydrogen sulfide can also contribute to the undesirable ‘cooked’ flavour in milk. It is generally accepted that the ‘cooked’ flavour appears in milk when heated to 76.5°C instantaneously, 71°C for 15 minutes, or 68.5°C for 30 min (Josephon, D. V. 1954).
In an ice cream mix, both the ‘cooked’ and ‘eggy’ flavours will begin to develop at above 72°C.
Because hydrogen sulfide is formed predominantly in the egg white, and because it is primarily the lecithin found in egg yolks that contributes desirable characteristics, it is better to use only the egg yolk portion of an egg for ice cream making.
Greater quantities of hydrogen sulfide are produced when the egg is older. For this reason, it is important to use fresh organic eggs in ice cream making.
A hen’s diet can also influence the flavour of an egg: fish-meal feeds, raw soy meal, and certain feed pesticides can cause off flavours. Hens fed a nutritious feed will therefore produce better quality eggs.
Storage and age play a significant role in egg flavour. Egg quality deteriorates as much in a day at room temperature as in four days under refrigeration, and almonella bacteria multiply much faster at room temperature (McGee, 2004).
It is best to buy eggs cold out of the fridge, not off an open shelf, and keep them cold.
An airtight container is better than the standard loose carton at sowing moisture loss and the absorption of odours from other foods, although it accentuates the stale flavour that gradually develops in the eggs themselves. It is, therefore, to use fresh organic eggs and not store them very long.
Josephon, D. V. 1954. Review of chemical mechanisms affecting flavour acceptability of dairy products. J. Agr. Food chem. 2:1182
Marshall et al., Ice Cream, Sixth Edition, 2003, p.34