12/04/2018 at 5:05 PM #2191
As a fanatical home brewer, your last science this made me cry a little.
Andy – If your beer tastes like Marmite there are a couple of potential problems. The most likely is that you made the mistake of reading the instructions on the kit. They always tell you to brew too hot. You want to brew at 16-18c, and not the 25+ the kits tell you to use.
Cameron – Unfortunatly the sheer stresses involved in forming your thin film would tear the yeast apart… Remember, you are dealing with biology here not chemistry.
T-Bag – Look up original pussy beer. Go on. You know you want to….
Hsppy to discuss brewing… At length… Brewers are even worse than chemists when it comes to micromanaging the brew process.
Dave (long time listener, first time commenter)08/06/2018 at 12:44 PM #2202
OK… So just catching up on my commenting. I’m a bit behind. Things would be so much easier if I dodn;t have to work for a living…
Andy – yes, your reasoning for why the instructions say to ferment hot is current, but your reasoning on the mechanism isn’t. It does make fermentation go faster. The reason is that yeast metabolism goes up as the temp goes up (to a point obviously.. Then it dies) but also becomes less efficient. They get lazy and don’t complete the full pathway and you get off flavours developing because they are releasing compounds that would normally be metabolised. Higher temps also stresses yeast and can caused increased rates of autolysis (cell death and breakup). Vegemite/Marmite flavours are normally autolysis flavours – the taste of dead, broken up yeast cells. In small qualities autolysis gives a bready taste to some wines like champagne (they leave the wine on the dead yeast for a while to develop the flavour). In large quantities it makes your beer taste like Marmite.
Cameron – This is an enzyme driven reaction but remember that the enzymes are inside the yeast. This is cell metabolism. The cell brings in glucose through the cell menmbrane and metabolises it into energy through a long pathway with many enzymes involved. The waste products are co2 and alcohol. The limiting factor of the reaction rate isn’t enzyme activity it’s the rate at which the glucose can move through the cell membrane. That’s by osmosis and that is limited by the concentration gradient. If you make the sugars too concentrated outside the cell though you can cause the cells to move so much sugar inside that they will literally explode. This is called osmotic stress. Biology is complicated.
Bulk T-bag (I should call you catering pack) – since Andrew is too chicken to read out what I wrote originally, you might want to check outthe brewery wh last year did actually brew a beer with yeast cultured from the brewer’s beard. I think it was dogfish head brewery.
Dave08/06/2018 at 11:42 PM #2205
Just to add to Dave’s last comment. The Russian River Brewery in California does one batch of beer made by spontaneous fermentation every year. Basically they brew the beer and don’t add any yeast. Instead they put it in a corner of a room for a while and it takes up whatever yeast and bacteria are around before fermenting it. I think it’s called Beatification and it tastes different every year depending on the conditions of the room. I tried it in 2017 and have to admit I didn’t like it. Best thing is they sell it for 20USD the bottle and it is usually sold out in days.
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