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Heating the milk is not for thickening, it's for safety (so far as I've heard). Were your directions to either scald the milk or use powdered (ie., 100%powdered milk), or did they say to add powdered milk to room temperature milk? As long as you're using skim milk, you should be adding powdered milk for thickness. Not too much, though, or you will get gummy yogurt.

How long did you cook it?

You won't get Fage style yogurt from your machine. Especially with skim milk, you'll get a looser yogurt than what you're used to buying. It may go totally liquid if you stir it. If you want Fage, you'll have to drain the yogurt after it's done.

Sounds like maybe your milk spoiled or you cooked too long. But usually, cooking too long also makes it thicker.

It took us a few times to get ours to come out how we liked it (consistently).

I don't use a yogurt maker, but definately, the longer it sits, the more tart it becomes. The temperature also makes a difference. At a temperature the bacteria like, they'll multiply a lot faster, so the tanginess increases faster. At a slightly higher or lower temp, they don't grow as fast. Which is why it doesn't change much once you put it in the fridge.

The reason you heat the milk at the beginning of the process is so that you kill any existing bacteria, so they don't compete with the baterica you're introducing. If the existing bacteria happen to like the same environment as the yogurt bacteria, you could end up with spoiled milk.

As for thickness, after a certain point, it's as thick as it gets. Personally, I don't like the flavor or texture of the freshly made yogurt. I always strain it.

I also don't add powdered milk. I tried it a couple times and didn't like the flavor or texture of the finished product. Some people like it, though.

It's an experiment. It will probably take a couple of attempts before you get it to turn out exactly the way you want it to.

I use a Waring Pro model and I make yogurt at least once a week. This is a long response, but I wanted to answer as many questions as possible. I think your issues can be cleared up once you get a better understanding of the science behind yogurt. Yogurt is a product of fermentation - a simple chemical reaction, but a controlled reaction will yield consistent results.

We'll start at the beginning with the starter! Fage is a fine starter because it does have active cultures but also the "right" cultures. Why do I say "right"? It doesn't contain Bifidus. The science behind not having bifidus is pretty compelling, but it might bore you. Let's just say that Bifidus doesn't play well with others and tends to overgrow the other more community minded strains. So if you're looking for the "gut health" benefits of yogurt, use starters containing active cultures of: Lactobacillus bulgaricus, L. acidophilus and/or S. thermophilus and avoid any containing bifidus. Also don't use starters with sweeteners, flavorings or thickeners.

I won't do an entire bio lesson about the cultures and the fermentation process. The basic idea is that the cultures "eat" the milk sugar - lactose - and the result is lactic acid. The other half of the "science" story has to do with fat content.

I'm a bit of a geek, so I know that amount of lactose varies between milk products. I did a little playing around and figured out that the fat content of milk used to make the yogurt determines how much tang the finished product will have. Low fat milk products have more lactose and so the finished yogurt will have more lactic acid - hence more tang. So, if for example you start with heavy cream instead of skim to make your yogurt you wind up with a yogurt which has a more mild flavor, it also thicker and separates less. Why use heavy cream? It will still whip up into "whipped cream" after fermentation, it works well as an ice cream base and for those that can't have lactose, if you "cook" the cream long enough, you'll give the starter enough time to break down all of the lactose.

The amount of time yogurt is cooked will also determine how much of the lactose is broken down. So longer cook times will convert more lactose to lactic acid and thus be more tart. I make yogurt for several health reasons. The one relevant here is the inability to digest lactose. Yogurt "cooked" 24 hours (yes longer than the directions and the programed timer allows), you get a virtually lactose free product - 36 hours for cream.

Since we're using the same yogurt maker, cooking temp is one variable I don't need to address, so let's talk about texture. Right of of the machine, no matter what the fat content, the yogurt will not taste "right". It needs to "rest" in your refrig at least 8 hours. Once cool, you'll notice that the yogurt has separated at bit. When you use skim or low fat milk, the liquid will be very tart. You might want to drain some of that off if you don't care for the level of tartness you're getting. The more fat in the milk you began with the thicker your resulting yogurt, which is why a lot of fat free and low fat yogurts and cheeses have added starches or other thickeners like gelatin.

Powdered milk bumps up the protein level of the resulting product, but technically isn't "true" yogurt. Since you didn't heat the milk before beginning the process there may be a few other things going on that will affect the taste and safety of the finished product. Using just powdered milk might be an option to consider from a safety point.

Heating the milk prior to making yogurt ensures that unwanted organisms aren't given the chance to "chow" down on the lactose feast you intended for the starter. Have you ever left the milk out on the counter? The resulting product underwent the same reaction as yogurt but in an uncontrolled environment. The soured milk smells bad, has a bitter taste and undergoes yucky changes in texture. This is because lots of microbes and yeasts joined the party. These organisms are always in milk even after the pasteurization process. So, perhaps your method is part of the issue. Heating the milk kills everything; it's an effective "bouncer" allowing only your starter to enjoy the lactose fest party.

Heat milk to only 180 - 185 F - no more and then let it cool to less than 100 but so it's still warm. Skim milk and goat milk are more "tender" than whole milk, so be careful. Heating them too high will result in an off flavor. I admit to cheating - I use my microwave to heat the milk. I have a pre-programmed button for gentle heating, but even cheap models have some sort of 1/2 power setting. That might solve the issue of no stove.

The last tip about texture. Are you familiar with the cooking technique of tempering? I suggest you use that to incorporate the starter. A you don't want to shock your starter, but it will help give you a smooth "base". Also just to be sure I get a smooth product, I use a small strainer. I pour the base through the strainer to fill the jars.

I'm not sure if you're making yogurt because it's way cheaper than commercial products, you just like the taste, for general nutrition or other health reasons, but I hope this helped answer some of your questions. Have fun and enjoy playing with your food!!