Understanding the ionic composition of water is essential for reliable production and product performance.
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amino acids is low in fermentations, yeast may be forced to reduce sulfate (S(VI)) to sulfide (S(-II)) via sulfite/sulfur dioxide (SO2, S(IV)) and can result in excessive accumulation of sulfite. From our research at Oregon State University (OSU), sulfur dioxide can be removed but requires careful distillation for effective removal. Of the two species carbonate and hydrogen-carbonate (also known as bicarbonate), it is the latter that is the more relevant, at least during brewhouse processes where the pH is distinctly acidic. In any case both reduce the activity of free protons, thus opposing the proton release induced by calcium: 2H+ + CO32- ⇌ H+ + HCO3-
H2O + CO2
Carbonates are twice as effective at sequestering protons as calcium ions are at releasing them. So an excess of (hydrogen) carbonate in water will result in elevated pH and can adversely affect both amylase activity (essential for starch conversion to fermentable sugars) and consequently the separation of the fermentable extract from the unsolubilized grains. So in practice, for spirits based on starch hydrolysis, it is advisable to keep total carbonates below 20 mg/l. Phosphates are at the heart of all living organisms, being constituents of DNA, RNAs, ATP, ADP, etc. It therefore occurs naturally in all organic raw materials and they have outstanding buffering qualities. At typical mashing pH values (pH 5.2 – 5.6) phosphate is present mainly as H2PO4- with typical levels of phosphate in clear wort of the order of 700 – 900 mg/l (ie ca 10 mM). Nitrate is found in water and in itself is relatively harmless. However, it can be readily reduced to nitrite in water and by spoilage organisms. Nitrite is considered a likely carcinogen to humans and can also react with amines to form carcinogenic compounds such as N-nitrosodimethylamine. More generally, the presence of nitrites in water indicates pollution and can be toxic to yeast. Understanding the ionic composition of water is essential for reliable production and product performance. Today, there is less need to co-locate production facilities at sites of acceptable water quality and quantity and in the second part of this article we will discuss water treatment in the context of its use. Paul Hughes, Ph.D. is assistant professor of food science and technology at Oregon State University in Corvallis, OR. For more information visit www.oregonstate.edu or call (541) 737-4595. WWW.ART ISANSPI RI TMAG.CO M