Robert Poor’s Weblog

On this day in history: November 7 1929, The Museum of Modern Art in New York City opened.

Questions, always with the questions…

Today’s batch tries to answer a few different things:

• Is there a difference between Nancy’s Organic Yogurt culture and Voskos Greet Style Yogurt culture?
• What happens when you use almost sour milk as your base?
• Does warming the base first make a difference?
• Does it make a difference whether the jar is tightly sealed or open during incubation?

The process

As usual, I started with eight wide-mouth quart jars, cleaned and dried in the dishwasher. Each jar was given a label, A-H. The table below details the differences for each jar.

After filling the jars with 700 ml of base liquid (milk, or in one case, powdered milk, milk and water), I put four of them (A-D) in the microwave for 15 minutes. To the other four jars (E-H), I added 1/4 cup of culture, shook vigoursly and set them aside.

At the end of 15 minutes, I was hoping that the first four jars had gotten heated to at least 130 F, since many recipes call for heating the milk to 180 briefly in order to kill any bacterial. But when I measured, the liquid was only at 120 F. No matter — I went with that and put all eight jars (A-H) in the insulated cooler in a water bath. I inserted the aquarium heater and let the temperature of the liquids stabilize for an hour before adding culture to the jars that were previously too hot (A-D).

I gave all the jars an extra good shake to make sure the culture was mixed in, then removed the lids from half of the jars (see the table below for which jar got which treatment).

Culturing started at 9:30pm. I’m planning on a 7.5 hour incubation. That’s longer than usual, but I’ve been waking up at 5am regularly, so this is convenient.

Today’s Innovation

In the last batch, I put the aquarium heater in its own jar in the middle of the insulated cooler in order to keep it from falling into the water bath. My thought was that the thermal conductivity of the glass and water was good enough that everything would settle into the same temperature. It didn’t really work out that way — the water in the rest of the bath was 5 degrees cooler than the water in the jar with the heater.

Heater Holder

So in today’s batch, I simply cut a hole in the top of a plastic lid and used that to prop up the heater. While I was at it, I poked another hole in the lid and put the thermometer there — that’s much easier than dipping the thermostat in and waiting for it to stabilize each time I want to make a measurement.

This seems to be working well.

The Variants

Notes:

• “old milk” = Trader Joe’s Organic 1% with a date code of 19 October (today is 7 November). It’s not yet sour, but my nose detects a distinct tang.
• Horizon 1% = Horizon Dairies Organic 1% milk, purchased recently.
• Nancy’s = Nancy’s Organic Nonfat Yogurt, with L. acidophilus, S. thermophilus, L. bulgaris, L. casei, L. rhamnosus, B. bifidus
• Voskos = Voskos Greek Style Yogurt “Thick and Creamy Style”, with L. acidophilus, S. thermophilus, L. bulgaris, L. casei, B. bifidus. It turns out that the texture is a result of straining the yogurt, not due to any special culture.
• pre heat? = brought to 120 degrees F by putting in microwave for 15 minutes. My intention was to get it hotter — as high as 180 degrees F — in order to kill any lingering bacteria, but impatience won out.
• sealed? = cultured with the jar lid screwed on, otherwise left open for the duration of incubation.

The Results

You’ll have to check back on the next post.