High Gravity Brewing

Ken writes:

I’m studying for an exam on Thursday. The exam covers wort boiling, fermentation and maturation and much and more besides. Today I’ve been reading as much as I can absorb about yeast. One of the little tidbits that interested me about yeast is that lager yeast is a hybrid of the traditional strain saccharomyces cerevisiae, which had been used since time immemorial and another strain, quite possibly saccharomyces bayanus, which somewhere along the line derived from another strain saccharomyces eubayanus, which is native to Patagonia and which somehow travelled to Europe perhaps blown on air currents some 600 years ago. Most brewers’ yeast is what they call aneuploid, meaning that it has doesn’t have a regular multiple of copies of chromosomes. Yeast basically have sixteen chromosomes, but the Weihenstephan (lager) yeast used by many breweries has three copies of chromosomes 8, 10 and 11 and two copiesof all the rest. So 35 chromosomes in total, 15 of which are saccharomyces cerevisiae, 12 are not and 8 are a mixture of s. cerevisiae and s. bayanus (I think). Of course, as interesting and peculiar as that it, it’s not actually what I have to know for the exam. I have to know about the metabolic pathways responsible for the principle byproducts of fermentation ethanol, carbon dioxide, glycerol, and the esters aldehydes and higher alcohols that together give beer its characteristic taste. It would be helpful for me to blog about that in detail, as a way of fixing it in my mind, but there’s simply too much to say. So, instead, I’ll pick a smaller topic, namely high gravity brewing.

High gravity brewing is brewing with concentrated wort and then diluting down to sales concentration at a later stage. It’s basically watering down your beer, only if you think about it the water was going to be there anyway it is just a question of when. Brewers brew at high gravity because it is the cheapest way to expand brewery capacity. You don’t need a bigger mash tun or boiler or bigger fermenters, you just need to add a couple of tanks at the end of the process for the dilution water and for the extra beer. So it involves a saving in capital expenditure. BUt it also involves a saving in energy costs. The boil accounts for about 35% of the total electricity demand in the brewery. If the water were added at the start of the process a bigger volume of wort would need to be boiled which would be more expensive.

Tennents' Well Park Brewery, Glasgow.
Tennents’ Well Park Brewery, Glasgow.
And another picture

High gravity brewing presents a technical challenge to brewers, especially if they are trying to preserve the taste profile of an existing beer. For one thing, hop utilisation rates drop when the wort is more viscous and then the hops are going to have to stretch further because of the dilution. So brewers have to either swap to a more efficient form of hopping or increase their usage or top up bitterness at the end of the process using isomerised hop extracts. Additionally, fermentation is affected by the different make up of the wort. Yeast is placed under osmotic pressure due to all the sugars in the wort. And when it ferments it all down, it is put under stress by the highly alcoholic environment. Also the wort contains more amino acids which can be used to produce esters or higher alcohols. Wort is sometimes aerated mid way through fermentation to take into account the flavour changes. The yeast used in high gravity brewing has to be more flocculent because in more viscous wort it takes longer to settle. Then of course the dilution water has to be up to scratch. It has to be microbiologically sterile and especially if it is added after fermentation it has to have next to zero dissolved oxygen in it (less than 100 parts per billion). And it is a non-trivial matter to blend the beer with the water evenly while getting the respective ratios right.

The estimated savings, though, are like Christmas time for accountants. Brewhouse savings of 38%, wort cooling savings of 25%, space cooling savings of 15%, pumping savings of 20%, cleaning savings of 20%, personnel savings of 20% and a reduction in space needed in fermentation and storage of 22%. So high gravity brewing is how large commercial companies do it. And, realistically, the only thing stopping the smaller companies doing it is that they don’t have the sales to justify it–at the moment. But there’ll come a time when the micros are just on the verge and the temptation to brew at high gravity will probably prove irresistible.

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