About yeast

So I was visiting my friend (a chemical engineer), and it was beer brewing day. to control the temperature he uses a little "Arduino" board, that can communicate with e.g. MatLab.

We wanted to find the best way of "starting" the yeast for the brewing, so I looked online, and found that yeast is actually pretty tough - I told him to add a little sugar in some water with the yeast.

This answer of cause does not satisfy anyone, so I decided to do a little home experimenting. Knowing that I wouldn't want to spend the whole week, I opted for the little experiment, using no replications and only 20 samples.

The experiment was as follows:

Find out how best to start your yeast. I assumed that sugar and salt were deciding factors, sugar speeding up the growth and salt slowing it/killing it. The concentrations I tested were of the top of my head (no literature search here), so only one of the parameters had good values.

For testing salt and sugar I used beer bottles, as they are easy/fun to come by, and to measure yeast activity I used balloons. Yeast produces CO2 as it ferments sugar, so the bigger the balloon, the healthier the yeast.

See the setup in the picture below.

The result are pretty clear I think, though they deserve a little commenting.

• It seems that no salt and 4% salt are worse for yeast than 0.5-2% salt.
• For sugar the it seems that the sweeter the better, and my 4% were not high enough to inhibit the yeast growth. The yeast article on Wikipedia seems to indicate that sugar should inhibit the growth at some point.
• Yeast doesn't do anything in salt water.

This last comment might seem obvious, but it is not so as it was not only salt I had in the top five bottles. My first attempt on this set-up used dry yeast, which I had dissolved in water at 1% w/w concentration. All of the yeast died! So now you know that you should never try to start dry yeast in pure water (in Denmark there's no additives in dried yeast, while in other countries you can get it with e.g. ascorbic acid and growth medium, in which case it might work with pure water). This dead yeast concentration was added to the bottles prior to the live yeast being added, the latter only added after 6 hours of no activity. One could argue I should have redone the whole thing, but I thought it interesting to see if live yeast could "eat" dead dried yeast (the top row). It doesn't look like it.

So to sum up: If you want happy and strong yeast in your dough, use 0.5-2% salt, and at least 4% sugar. Word of advice, I'd go for 2% salt, as it tastes better, and improves the structure of the bread (less dry, tougher).

Feel free to copy and improve on this. In my humble opinion it's a great little experiment for school as well as for the curious kids at home.