G'Day All, I have asked this in a round about way before, but I'll ask again.

With my agricultural background, one thing we learnt was always addressing the "most limiting nutrient", when looking at the maximum growth or productivity of whatever your endeavours.

This gets me onto yeast growth and brewing performance. I have seen in the past that you fellows hate generalizations, but lets assume we have a typical 1.050 wort. And our starters are of the same level. We oxygenate these so that oxygen is not a limiting nutrient, at least in the growth stage of the yeast. And we are pitching recommended levels. In other words we are good brewers that do everything right.

Now a typical wort while supplying good nutrition for yeast, does not supply optimum levels of nutrition. There is room to feed the yeast, to increase its mass, as well as better its brewing performance. No better example of this is zinc. Additions of a few ppm of zinc makes a noticeable increase in the performance of the yeast. In fact more and more brewers add zinc in some form.

So from my agricultural background (here comes the generalization).

For my typical oxygenated 1.050 wort.

1. Is zinc the most limiting nutrient in a typical wort?

2. if not what is, and what levels are in the wort, and what levels need to be aimed for.

But I have more. I, like many brewers, add zinc, and this has shown a marked improvement in growth and performance. It’s no longer the limiting nutrient.I have to wonder if there is now another nutrient that could be addressed.In the unfamiliar world of generalization, I know you will say it will depend on the water. Let assume we have Pilsen type water, very soft. We are good brewers and do get our Ca levels up to 50ppm, with CaCl or CaCO3 in the mash. We might even add a touch of Epson salts, to get our Mg levels up another 2 ppm to be safe. And we practice all correct brewing processes, i.e. pH adjustment.

So,

1. What would be the next most limiting nutrient a brewer should consider in his wort. You may wish to split this into growth nutrient and brewing performance nutrient. Can you give, say, give the next two nutrients.

2. And what levels are in a typical wort, and what should we aim for.

Thanks,
Graham Sanders

RESPONSE:

Graham, You are absolutely right... although we like generalization it usually never works. Typical wort...???!!!

But we will try.... zinc is definitely a limiting factor in most worts. The zinc concentration depends on malt quality, hops, equipment used, brewing water... Usually malt would supply a sufficient amount of zinc but more than 95% of it is lost during lautering. Zinc builds a complex with phytic acid and this "large" molecule is held back in the spent grain during lautering.

In older literature a zinc concentration of 0.15-0.2 ppm is recommended.

More recent publications recommend higher zinc concentrations around 0.3ppm. In trials in our lab we found improved fermentation performance with zinc levels up to 0.5 ppm depending on the zinc source.

In propagation the zinc levels can be even higher because the each yeast cell is divided more often and therefore the zinc pool is divided more often as well. To maintain a sufficient zinc pool during propagation the yeast needs to take up more zinc from the wort than during fermentation.

It is very difficult to give a typical zinc level in wort. During our studies we found zinc levels from 0.01 ppm - 0.25 ppm in all malt worts. As we mentioned above the zinc concentration depends on so many factors. Now to other limiting factors. You probably want to check your free amino nitrogen level in the wort. If you do not have sufficient amount of free amino nitrogen you will end up with stuck fermentation and a change in your flavour profile. This is a main concern if you brew high gravity or use adjuncts like sugar or corn syrup which do not contain any free amino nitrogen. All malt wort (12 P) is usually sufficient with 150-220 mg/L FAN.

You also should check the ratio of Mg and Ca ions in your wort. The ratio should be more in Mg favor. So if you add calcium you should consider adding magnesium as well.

Regards,
Forbes Waldrop & Tobias Fischborn