The first post in this series is here. Six days in, our mead-to-be is bubbling along nicely. We have reached peak bubbling of about a bubble every two seconds in the airlock, look:

Bubbles in jug and airlock

To recap, we have put yeast into a solution of honey and water, shaken it, and waited. What is going on in there?

My friend Saccharomyces cerevisiae ICV D-47

Let us get to know this worthy fellow — Saccharomyces cerevisiae. Out of the many single-celled yeasts out there, that is the one we humans have chosen to adopt. This is the yeast that brewers and bakers cultivate; we see it sold on grocery shelves under various labels: active dry yeast, instant yeast, bread-machine yeast, wine yeast and so on.

Saccharomyces cerevisiae — the brewer’s and baker’s yeast from MicrobiologyOnline.org

What is so special about it? Beats me, but I got some clues from my obsessive googling. It reproduces quickly — in an hour and a half, it can double its population. It can ferment both in the presence of oxygen and outside it. In the presence of oxygen it ferments faster. Without, it goes slower. But ferment it does. As for reproducing — it can blithely switch between simply diving into two, like a plant, or having male and female babies that have sex to produce babies, the familiar way.

Yes, all of this parade of life is going on in the glass jug while it ferments.

Actually seeing a microbe with a naked eye is not something one usually aspires to (you could fit about two hundred of these, end-to-end, within a single millimeter of your tape measure). But one of the talents this yeast has is to ‘flocculate’. What that means is that individual creatures come together into a ‘floc’, which sounds conveniently like ‘flock’. If only all science words were so conveniently named. Now a flock is actually visible, it looks like brownish residue — as you see below in the picture:

Floc of yeast

Another way you can actually see it is: next time you buy some red grapes at the store, dust off the whitish powder that you find on its surface. This is nothing but our friend Saccharomyces cerevisiae.

Yeast on grapes from http://www.providentliving.org.nz/

In fact the exact strain of this yeast that we used — ICV D-47 — was dusted off grapes originally in France by a man named Dr. Dominique Delteil, somewhere in the 1980’s.

Airy fermentation

I think of fermentation as ‘incomplete eating by a microbe’. ‘Incomplete’ because even after the microbes have had their fill, there is plenty of stuff left over for you to enjoy, whether it is wine, beer, bread or dosa. ‘Eating’ because that is what the microbes are doing, gorging themselves silly on your sugars, gaining energy enough to meet, marry and multiply. Why only microbes? Because clearly, you would not look very kindly at bigger creatures gorging on your food — we would call them pests.

Our mead right now is in the process of fermenting in an airy way (aerobic fermentation). Remember we shook the jug to allow air to disperse throughout the liquid? Well the yeast is rapidly using that oxygen to produce the bubbles of carbon-dioxide that we see filling the airlock.

These are the same bubbles that we aim to trap inside a loaf of bread to make it rise. In this case, we allow those bubbles to escape. Because what we care about (the alcohol) will come about after all the oxygen has been used up, and we go into the next stage. Stay tuned….