Wed, Jan-25-06, 13:06
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Registered Member
Posts: 4,909
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Plan: Atkins,PP - wgt in %
Stats: 100/96.8/69
BF:DWTK/DDare/JEnuf
Progress: 10%
Location: Vancouver Island, BC
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Actually, I was thinking of this part:
Quote:
{edited a bit re pics and diagrams}
Traditionally, yogurt has been made in the Balkans and the Middle East by heating the milk to partially remove water. When the temperature of the milk reaches 85°C, {ok, that would be 185°F, I misremembered} one particular micellar protein (kappa-casein) at the surface of the casein micelles reacts with one particular whey protein (beta-lactoglobulin). This interaction produces minute 'bumps' on the casein micelle surfaces ... The beta-lactoglobulin-kappa-casein complex later prevents other casein micelles from getting attached at these sites. 'Later' means when yogurt bacteria metabolize lactose and produce lactic acid and the milk starts to coagulate.
The surfaces of the heated casein micelles are partially blocked, so only a few micelles can interact. This leads to the formation of short branched micellar chains. When the coagulation is complete, the milk has changed into a gel. {this be yogurt, as we know and love it  } Under an electron microscope, the gel looks like a sponge with small pores filled with the whey ...
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All that being said, for foodsafe purposes, 160F for 3M is sufficient for beastie control if that's a concern...so they tell me  -- and I definitely don't want to range much around 190F because that's uncomfortably close to boiling temp for me and that changes the flavour of the milk considerably, as well as fully denaturing/cooking those milk proteins (hey, probably related).
Quote:
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The unique microstructure of yogurt means that all the liquid (whey) is immobilized within its body. Of course, no consumer would like to buy yogurt from which whey separates easily. This would be a sign that the yogurt is susceptible to ‘syneresis’, and that there was something wrong in the yogurt manufacture. If, for example, the milk is not heated at about 90°C for a time long enough (about 15 min), larger pores may develop in the yogurt body in some areas and larger clusters of casein micelles may develop in other areas. {i.e., the yogurt breaks and weeps, doesn't have a consistent small pore size gel} The whey then starts showing in the containers during storage. To be on the safe side, some yogurt manufacturers use small additions of various 'thickening agents' such as starch gel, various plant gums or pectin to the milk to improve the retention of water in yogurt. Water may also be retained in the yogurt by increasing the amount of milk solids but in this case the reduction of the pore sizes changes the overall mouthfeel of the yogurt and is not desirable. The preceding statements about the solid nature of yogurt are correct considering the so-called set-style yogurt. There is also a liquid yogurt variety on the market. It is made in the same way as set-style yogurt and then is pumped into retail containers, whereby the body of the yogurt is broken into small particles, which allow the yogurt to be poured. {yup, shake it or stir it before it's set -- which is finalized while chilling in the fridge, by the way -- and the delicate gel is 'broken' and it pours...or you can make yocheese by filtering/draining it}
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It pretty much appears to be an ART to getting the time and temp right, right there between 185F and 190F, especially for milk yogurt, which will be thinner than a cream yogurt (if we're talking basic dairy products as a base).
Last edited by IslandGirl : Wed, Jan-25-06 at 13:23.
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*grump*
~Gail
Linear Mode
