The Yogurt Diaries
October 18, 2008
Today’s batch will be an exercise in different culture media. We have low-fat organic milk. We have organic powdered milk. We have goat’s milk. And we even have sweetened, vanilla flavored soy milk. I have little confidence that S Thermophilus and L Acidophilus will find soy milk a hospitable environment in which to grow, but I thought I should try with one sample.
Here are the samples, ready to be heated in the microwave (of course I remove the metal tops first).
Samples ready for pasteurization
As before, I heated up the quart jars, four at a time, in a microwave oven to bring the temperature of the contents up to 130.
Microwaving the milk
I’m incubating the samples in a water bath in an insulated cooler. To keep the temperature stable, I’m using an aquarium heater. So the heater won’t tip over (that could be very bad, electrically speaking), I put it in its own jar in the middle of the cooler.
Heater set for 110F
After heating the samples up in the microwave, I moved them to the insulated cooler, along with an aquarium heater, and let them sit until their temperature stabilized at 110 degrees.
I then added 1/4 cup (4tbsp) of Pavel’s Russian Style yogurt to each jar, shook vigorously to mix in the yogurt culture. Here, you can see the samples ready for incubation.
Ready for incubation
I incubated the batch for 6.5 hours. I was expecting a temperature of 110F, but when I measured the water bath after 6 hours it was at 105F. This is probably because the heater was in its own jar. The thermal conductivity is good, but this approach probably reduces the amount of convection currents in the water. (Note to self: in the future, consider an aquarium circulation pump.)
Here’s the line up of the samples. Each sample had 60 ml (1/4 cup) of Pavel’s yogurt added as a culture.
- Sample 081017 A: 800 ml goat milk
- Sample 081017 B: 800 ml Kirkland Vanilla Soy milk
- Sample 081017 C: 800 ml water, 3/4 cups powdered milk
- Sample 081017 D: 800 ml 1% Trader Joe’s Organic Milk, 1/4 cup powered milk
- Sample 081017 E: 800 ml 1% Kirkland Organic Milk
- Sample 081017 F: 800 ml 1% Kirkland Organic Milk
- Sample 081017 G: 800 ml 1% Trader Joe’s Organic Milk
- Sample 081017 H: 800 ml 1% Trader Joe’s Organic Milk
Surprisingly, all of the samples, including the soy milk based one, appeared to have set nicely.
In retrospect, I shouldn’t have been so surprised: I looked up “soy milk yogurt” on the web, and learned that sweetened soy milk is a perfectly good medium for culturing yogurt — you even use ordinary dairy yogurt as your starter.
The results of taste and texture tests will be next…
The Yogurt Diaries
October 17, 2008
Maria and I bought an insulated cooler, able to hold eight of the wide-mouth quart jars I’m using for yogurt. That, plus the nifty 50 Watt aquarium heater I modified, will do a good job in keeping all the yogurt incubating at 110 F.
So today I’m making eight quarts.
Yogurt Batch 081906 [A-G]
- Wash 8 wide mouth quart jars in heated dishwasher to make sure they’re clean.
- Fill each jar with 800 ml of low-fat (1%) organic milk. This batch was from Costco.
- Heat the jars, 4 at a time, to 130F in a microwave oven. This required 15 minutes for each batch in our little Sanyo microwave. The milk started at about 40F, and I measured a 30F rise for each 5 minutes in the microwave.
- Stand the jars in a water bath in the insulated cooler with the aquarium heater — let stabilize to 110F.
- Added the following cultures for the different samples:
- Sample 081906 A: 4 tbsp Mountain High yogurt
- Sample 081906 B: 4 tbsp Mountain High yogurt
- Sample 081906 C: 3 tbsp Mountain High yogurt (I was running out)
- Sample 081906 D: 4 tbsp Pavel’s Russian Style yogurt
- Sample 081906 E: 4 tbsp Pavel’s Russian Style yogurt
- Sample 081906 F: 2 tbsp Pavel’s Russian Style yogurt
- Sample 081906 G: 3 tbsp Pavel’s Russian Style yogurt
- Sample 081906 H: 5 tbsp Pavel’s Russian Style yogurt (“shaken, not stirred”)
- Incubated all samples for 6.5 hours at 108F except for Sample 081906 A, which was incubated for 5.5 hours (we needed some yogurt in time for breakfast).
- Placed samples in refrigerator (40F) to halt incubation.
Incubation started at 0130. Should be done at 0800. More news then.
Notes
To mix the culture into the milk base, a bit of stirring followed by vigorous shaking appears to work well.
Don’t forget to measure how much water bath is in the cooler — if I know that, it will help me stabilize the temperature of the batch more quickly.
Results
Well, all the results were good. There was generally very little difference between batches made with the two yogurt cultures (Mountain High and Pavell’s), and the system seemed quite tolerant of different amounts of culture: there was not a strong difference between five tablespoons and two tablespoons of culture. Perhaps the two tablespoons batch (Sample 081906 F) was a bit “wigglier” and less creamy than the five tablespoon batch (Sample 081906 H), but the main lesson is that the process tolerates large variations in the amount of culture.
The Yogurt Diaries
October 1, 2008
The ineffable Maria and I like yogurt smoothies for our daily breakfast. And we like to make them with organic yogurt, but organic yogurt is be expensive. So I’m re-learning how to make yogurt, partly so we can economically indulge in our daily smoothies, partly to see what variations in texture / tanginess we like.
Last night I made the first experimental batch. Here are the lab notes:
Yogurt Batch 081001 [A,B,C,D]
- Wash 4 one quart (~1 liter) wide mouth canning jars in the dishwasher with heated drying. This does a reasonable job of sterilizing the jars.
- Fill each jar with three cups (0.7 liters) of organic low-fat (1%) milk.
- Immerse in water bath (in this case, in a slow cooker), heat water bath to 110F (43.3C)
- Once the bath has reached the target temperature, stir in 4 tablespoons (0.06 liters) of live-culture yogurt purchased at the local supermarket. In this case, we used Mountain High All Natural Plain yogurt containing L.Bulfaricus, S, Thermophilus, L Acidophilus, B Bifidus and L Casei.
- Mix well! It required a surprising amount of stirring to get the yogurt broken up and distributed though the milk.
- Wrap the jars and water bath in an insulating blanket and incubate. The incubation times for each sample:
- Sample 081001 A: 3h40m
- Sample 081001 B: 5h00m
- Sample 081001 C: 6h20m
- Sample 081001 D: 7h40m
- Put sample in refrigerator to stop incubation process
Notes
- Note that in traditional recipes, one heats the milk to 180F (82C) and then cools it to 110F (43.3C) before adding the yogurt cultures. This is to kill any other critters in the milk. I skipped this step, relying on the freshness of the milk and the cleanliness of the jars. If I’m patient enough, I’ll include this step in a future batch to see if it makes a difference, but it does take time.
- I used a modified 50W aquarium heater to maintain the temperature of the water bath, and measured it with a cooking thermometer. The heater worked very well, and temperature variations appeared to be less than +/- 1 degree F.
Results
All four samples had a thin layer of curd floating on top which was textured and slightly thicker in consistency than the rest of the yogurt.
- Sample 081001 A: (3h40m) — Much too runny. Flavor was fine, but it was really like thick milk with a yogurt taste. Should work fine in a smoothie or over granola, though.
- Sample 081001 B: (5h00m) — Good. Thin texture, but firm enough to hold up in a spoon. Light flavor.
- Sample 081001 C: (6h20m) — Very good. Firmer texture, slightly tangy flavor but still very delicate compared to the mother culture.
- Sample 081001 D: (7h40m) — Very good. The top layer of curd was somewhat thicker, and I could convince myself that the flavor was tangier than 081001 C. As a pragmatic point, it’s not clear that the extra 1h20m incubation time makes a real difference.
Commentary
Since a gallon (128 oz) of organic milk costs $6 at Safeway, and a quart (32 oz) of organic yogurt costs $4, we’ve essentially reduced our cost from $0.125 per ounce to $0.047. Assuming we use the yogurt from a previous batch as the culture mother for the next, a quart of yogurt that used to cost $4 now costs $1.50.
I liked the results, especially Sample 081001 C (6h20m incubation). Shorter incubation produced a thinner texture, longer incubation didn’t appear to make much of a difference. Skipping the lengthy “heat to 180 and cool back down” step didn’t seem to hurt the results, but might be worth trying. Ideas for future batches:
- get an insulated cooler for incubation. it will leak less heat, and I will be able to incubate six quart jars at a time.
- use “russian style” yogurt as a culture.
- use goat’s milk
- use skim milk
- use water as a base and add powdered milk. (do they make organic powdered milk? is it less expensive?)
