- Lactobacillus bulgaricus and/or
acidophilus & Streptococcus thermophilus
- What they do
- The streptococcus produces lactic
acid lowers the pH, thus
changing the form of the milk proteins and causing the mixture to
- The lactobacillus bacteria produce
acetaldehyde, acetic acid, volatile fatty acids, ethanol, carbon
dioxide and various other products which influence flavor and
- If streptococci outgrow the
lactobacilli, the result is a harsh, sour yogurt due to
overproduction of lactic acid relative to flavor components. The
ratio for proper taste is 1:1
- Fruit and fruit flavors are
pasteurized separately and added later.
- What is
- Yogurt is a fermented milk product
that can be made from any milk, even soy milk. A mixed culture of
Lactobacillus acidophilus (or bulgaricus) and Streptococcus
thermophiles (they work better together than they do separately)
produce lactic acid which lowers the pH and makes it sour. The
partial digestion of the milk (lactose) which occurs during
fermentation makes the lactose easily digestible, which is good
for lactose-intolerant people.
- Yogurt Facts
- a good source of calcium,
riboflavin and protein.
- has a fine curd which makes it more
easily digestible than sweet milk.
- lactose is converted to lactic
acid; this makes digestion easier on lactose- intolerant
- Lactobacillus acidophilus may
synthesize Vitamin B in the intestine.
- cultured yogurts are higher in
folic acid than other yogurts.
- lactic acid bacteria fight
pathogenic organisms: Salmonella typhi die, E. coli are unable to
develop, and S. paratyphi and Corynebacteriae diphtheriae lose
their pathogenic properties.
- fermented milk cultures have been
reported to help treat peptic ulcer, diarrhea, and dysentery.
- Freshly prepared yogurt contains
10,000,000,000 (109) bactria per gram
Factors for successful yogurt
- good sterile technique (proper heat
treatment and cleaning of glassware)
- proper incubation temperature.
Lactobacillus is killed if exposed to temperatures over
1150F, and does not grow well below
- keeping the starter uncontaminated.
Do not open the starter until you are ready to make the next
Food Uses (other than by
- Baked goods will rise well when
yogurt is used due its acidity. It can be used with excellent
success in baked goods, using it as part of the liquid in cakes,
waffles, pancakes and muffins.
- Yogurt is an excellent dish by
itself, but can also be used in place of sour cream.
How is yogurt different from
- Thermophilic (heat-loving) rather
than mesophilic (room temperature) bacteria used
- No rennet is added
- Curds and whey are eaten together
(Little Miss Muffet?!).
- Pasteurized milk is fortified with
skim milk (adds solids for body)
- Mixture is homogenized
- Bacteria added; culture allowed to
incubate in warm tanks
- Placed in containers and
refrigerated for sale
- For more firm yogurt, add 2
tablespoons powdered milk to the milk prior to heating. Either
whole or skim milk may be used, but whole milk makes richer
- The yogurt must be kept warm to
keep the cultures active, but not so warm that the bacteria is
killed (around 115oF).
- Longer incubation produces a more
tart taste, and more lactic acid. Do not over incubate : the curds
- Materials (per class
- 1/2 gallon milk
- 1/2 cup Dannon plain yogurt (4 oz)
- double boiler (or heavy pot) with
lid, cap. of 2 1/2 qt
- (2) qt bottles with lids, very
- (1) 8 oz jar with lids, very clean.
- candy thermometer, reading range
(100 to 200oF)
- 1 styrofoam cooler
- microwavable heat packs and
reusable ice packs would be handy
- 1. Heat milk to 125oF in
double boiler. If using heavy pot, stir frequently to prevent
sticking. Keep covered.
- 2. Immediately remove from heat,
place covered pot in pan of clean cool water until stirred milk is
very close to 115oF.
- 3. Stir up yogurt starter with a
clean fork, add to 115oF milk, stir thoroughly, (temp
should drop a little). Pour still warm mixture into the three
bottles, cap immediately.
- 4. Place filled bottles in
styrofoam cooler, add enough 115oF water so that
bottles are surrounded, but the lid
- rims are not touching water. Do not
disturb the yogurt and it will be finished in 3 hrs (temp. needs
to stay constant, around 110oF or so) refrigerate until
- 1) You disturbed it during the
incubation period. After stirring in yogurt starter, place in the
115oF "cooler" and do not disturb for 3 hours. It
should be gelled by then.
- 2) Many things could cause
curdling--too much starter, not properly stirred in at the
beginning, too much heat when too much starter is added. Unnatural
curdling comes from too much acid too fast, at too high a
Take the Yogurt
Quiz and see how you
return to food