Australians
drink an average of 106 liters of cow’s milk per year and this figure is
climbing, mostly due to the continuing uptake of milk-based coffees.
Milk
is a colloid (micro emulsion) of butterfat globules within a water-based fluid
that contains dissolved carbohydrates and protein aggregates with minerals.
100 gm's of full cream milk comprises of around 88g water, 3.9g fat,
3.6g fatty acids, 4.8g Lactose (the sugar form of Carbohydrate), 14mg of
cholesterol and 120mg of calcium.
The amount of fat within the milk will generally
dictate its sweetness and full mouth silky feel.
Interestingly, sheep's milk
contains 6 gm's of fat…wonder what that would taste like in a coffee? Hmm…
Heating milk for coffee.
Espresso machines use a steam wand to both heat and aerate
the milk creating micro bubbles within the milk structure giving a dense, smooth, silky
texture to the milk. This process is commonly known as ‘stretching the milk’ as
the volume in the jug will increase due to the heating and aeration. In heating
the milk, a chemical reaction is taking place within. The whey proteins and casein
proteins start to break down with the applied heat; this affects their ability
to continue to be aerated into micro foam. You only have one chance
to get it right, heat the milk too much and you’ll scorch or possibly boil it making it taste
burnt, watery and unpalatable, not heated enough, < 60C, and the micro foam may have not fully developed leaving flat warm milk. Never reheat milk; the proteins have already been
denatured and you will be unable to re-foam it. You'll be serving flat, poor tasting coffee.
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| Micro Foam. Should look like a jug of paint. |
Heat cold fresh good quality full cream milk keeping the steam nib just below the milk's surface and create a whirlpool effect. Heat to around 60 –
70C using a thermometer or a heat sensitive calibrated jug (see below) to build the silky micro foam you're looking for. Don't heat the milk too quickly, just open the steam tap 1/2 a turn. Heating past 70C the milk will
continue to break down and taste watery and potentially scold the
customer’s mouth. At around 100C, (remember its 88% water) you’ll boil it.
Judging the amount of fresh cold milk you need each time is
the art, do not reheat left over milk for coffee!
Keep all things milk related clean, fresh
and cold - jugs included. Better you have a reputation for great coffee than
save a few cents reheating left over denatured milk.
Speaking of Heat Calibrated Frothing Jugs:
Available now at Custom Coffees Bendigo.
600ml & 1 liter for commercial or home use.
