Wikipedia:Reference desk/Archives/Science/2012 April 13

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April 13

Fermented milk?

I had about .125 US gallons (0.47 L) left in a .5 US gallons (1.9 L) container of milk in my refrigerator that when I went to drink it today tasted distinctly alcoholic, and upon smelling it it appears that it also has an alcoholic smell. The expiration date on the milk carton isn't until tomorrow (April 13). Is it possible that the milk fermented somehow? If not, what else could explain the taste/smell? I am positive that no one has altered the milk since I last drank some on the 9th. Ks0stm ^{(T•C•G•E)} 02:25, 13 April 2012 (UTC)

Hmm, i've never noticed any alcohol taste and i've inadvertantly sipped off milk a few times. I don't think pasturized milk can ferment, but off milk can have some very strange flavors and maybe the very beginning stages can have an alcohol like taste... I think it's obviously possible that your milk went off one day before it's used by date: if someone drank out of the container and some bacteria got in; if it was left on the counter and allowed to warm up a bit before being put back; or maybe less likely but still possible is if it was incorrectly stored before you purchased it, there may be other reasons I haven't thought of.. Vespine (talk) 04:46, 13 April 2012 (UTC)

Looks like I was wrong about fermenting pasturized milk. That page does seem to be full of dubious claims, but they do say you can ferment pasturized milk, but they say you have to add specific cultures such as kefir which I think is unlikely to have happened by accident to the milk in your fridge. Vespine (talk) 04:50, 13 April 2012 (UTC)

The primary fermentation product of milk should be lactic acid, which does have a distinctive odor, and which may be confusing the OP's nose in some way. Decarboxylation of lactic acid should result in ethanol as a product, however I an not sure this happens to any great extent in sour milk. --Jayron32 04:56, 13 April 2012 (UTC)

@OP: Yes, you did smell alcohol. Why? Because your milk got contaminated by organisms that carry out alcoholic fermentation, probably yeasts. Where did the yeasts come from: the air, your hands or mouth, or it could have happened during processing or bottling, in short, the "environment". Milk readily undergoes alcoholic fermentation, just like grape juice, and there are dairy products that contain alcohol, like REAL kefir, kumis and blaand. Milk can also be used to produce wine [[1]]. Whether alcoholic fermentation actually takes place depends on the microorganisms present. USUALLY, but not always, lactic acid bacteria are present and metabolize faster than yeasts do, but conditions and starter cultures can be selected so that alcoholic fermentation is significant. In this case, the godess Fortuna chose a "starter culture" (the contaminant) that highly favored alcoholic fermentation. Also, the expiration date applies only to unopened containers. When you opened the jug on the 9th, the expiration date stamped on the cap lost all meaning. Dominus Vobisdu (talk) 06:08, 13 April 2012 (UTC)

If it was left in the fridge it shoudn't yeast ferment in under four days, far too cold for that. Any chance you had a power cut in those four days or someone else left the milk out for a few hours? SkyMachine ⁽⁺⁺⁾ 07:40, 13 April 2012 (UTC)

Some cultures drink the stuff anyway, see Kumis. --TammyMoet (talk) 09:13, 13 April 2012 (UTC)

We have an article on fermented milk products. 86.140.54.3 (talk) 15:09, 13 April 2012 (UTC)

Neurology

1.could it be generalized that as long as a man tired, and no external intervention has been administered..., he'll have more dreaming? 2.why do some people doesn't remember their dreams at all..., allegedly?. — Preceding unsigned comment added by 109.64.173.10 (talk) 03:08, 13 April 2012 (UTC)

Number one might be answered in the rem sleep article, number two has it's own section Dream#Recalling_dreams. Vespine (talk) 04:40, 13 April 2012 (UTC)

I remember dreams that occur just around the time I'm waking up. However, when you're in that in-between state, you kind of have to "replay" the dream contents in your head in order to remember details, and even then some of it will elude you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:22, 14 April 2012 (UTC)

Do sensory organs evolve to be too small to have sex with?

I have a half remembered fact that ears and nostrils evolved to be too small to be penetrated in order to avoid damaging them, is that true?Bastard Soap (talk) 13:43, 13 April 2012 (UTC)

Where did you hear that? It is completely false. Plasmic Physics (talk) 14:24, 13 April 2012 (UTC)

I don't remember where I heard it, which is why I didn't trust it. Are you sure it's false? It sort of makes sense.Bastard Soap (talk) 14:31, 13 April 2012 (UTC)

Sure, it sort of makes sense. Absolute drivel doesn't get passed around if it doesn't sort of make sense. Actually, the first time I heard that line was from a professional comedian :)

More seriously: surely there is selective pressure acting on the nostril size of any mammal. One set of factors can give benefits to larger nostrils, while other factors give benefits to smaller nostrils. The camel has the best of both worlds: large nostrils that allow free air flow, but can be closed on demand to keep out debris, etc. So, this general point is correct: mammals' nostrils are generally small enough to prevent them from being penetrated by foreign objects that they are likely to come across, while being large enough to allow good ventilation. --But there's absolutely no reason to think that apes have experienced more selective pressure on nostril size due to penises, compared to say, insects, or general debris. SemanticMantis (talk) 15:14, 13 April 2012 (UTC)

This is the most interesting question I have ever read. Nice! Debianista77a (talk) 19:52, 13 April 2012 (UTC)

No, small penises went extinct because they DID fit. Ssscienccce (talk) 20:06, 13 April 2012 (UTC)

Why couldn't they just evolve to be more robust so I could still get my nasal on? 203.27.72.5 (talk) 00:05, 14 April 2012 (UTC)

Since there's still other holes you can put a penis in non-reproductively, it's probably not the principal cause of their size. --Colapeninsula (talk) 11:53, 15 April 2012 (UTC)

This joke originates from a recent webcomic: [2]. Things apparently turn into urban legends quite rapidly these days. — Preceding unsigned comment added by 62.102.168.173 (talk) 13:48, 16 April 2012 (UTC)

Stale Petrol

In the now long-lost instructions for my petrol lawnmower, it said avoid using petrol that had been stored for over 3 months. A quick look on the internet confirms thats this may make it difficult to start the mower. What causes this deterioration, and is the petrol still suitable for use in my car? 86.137.136.167 (talk) 15:35, 13 April 2012 (UTC)

If it's a 2-stroke fuel (which means it has lubricant blended in) then the two can separate. Also, if the petroleum spirit is blended with ethanol (which is common in some countries, less so in others), the ethanol can separate out ("phase separation") producing a milky layer that won't burn well. 2-stroke fuel can't be used in a car engine; I wouldn't risk the proper operation of your very expensive car engine with some suspect petrol in any case. -- Finlay McWalterჷTalk 15:48, 13 April 2012 (UTC)

That's quite a disadvantage, then, meaning you have to find some way to safely dispose of all remaining 2-stroke fuel at the end of the mowing season, then buy all new fuel next year. I wonder if it could be reblended, somehow ?StuRat (talk) 16:35, 13 April 2012 (UTC)

You don't have to re-blend 2 stroke fuel. Its that same as a 2 stroke motor-bike. One puts the petrol in first then add a can of oil. Rock the bike forward then back (to mix), kick the engine over an' your away.--Aspro (talk) 19:29, 13 April 2012 (UTC)

I've seen the recommendation, and seen it frequently ignored, without any problems. Is it marketing garbage from oil companies? HiLo48 (talk) 17:59, 13 April 2012 (UTC)

Think this is just so that the manufacture can cover themselves. From experience I can tell you modern fuel in a an airtight containers lasts for years and a quick shake can remix any separation. However, a mower left outside (and they have a vented tanks) could more than likely suffer from water condensate forming at the bottom of the fuel tank and thus course starting problems. When stored in just a garden shed they don't cool down so fast at night (through thermal radiation). In this case moist air is less likely to condense in the tank because the air outside the shed cools down faster and any moister in the saturated air forms dew out there – that’s why you don't get dew on the carpets indoors. My old 4 stoke mower always (9 times out of ten) started on first pull with years old Regular (2 Star) fuel. Oil Compression engines have water agglomerators fitted to the fuel lines because water ruined the fuel pumps and aircraft are prone to get a lot of water in their kerosene/paraffin tanks. Classic cars have had problems due to being idle for long periods with water in the bottom of a tank of water saturated fuel -but this is a rarity. Just make sure the mower is almost empty before storage at the end of the mowing season store it under cover. A blanket shouldn't be necessary. And least I forget; pour cooking sherry generously over the lawn in early spring - it then grows already half-cut .--Aspro (talk) 18:47, 13 April 2012 (UTC)

I've wondered about stale petrol in the context of extended-range electric cars like the Chevrolet Volt -- if you drive it less than something like 40 miles per day and plug it in every night, you pretty much don't use the gasoline at all. Do the manufacturer or the critics say anything about this? Duoduoduo (talk) 19:32, 13 April 2012 (UTC)

I would imagine that over very long periods you are going to preferentially lose the lighter, more volatile, components changing the characteristics of the fuel. SpinningSpark 20:02, 13 April 2012 (UTC)

Does the fact that the fuel is stored in a confined tank make the evaporation of volatile components less of a problem? Duoduoduo (talk) 21:14, 13 April 2012 (UTC)

Yes. StuRat (talk) 22:16, 13 April 2012 (UTC)

More on "yes". If the container is sealed, the liquid will stop evaporating when the vapor pressure of the liquid equals the partial pressure of the liquid in the atmosphere over the liquid. If there container is almost full, this will be a negligible amount of material. --Jayron32 01:18, 14 April 2012 (UTC)

Although a plastic tank may allow some of the components to slowly diffuse through it. StuRat (talk) 03:45, 14 April 2012 (UTC)

To be honest, I wouldn't be too worried over the course of a few months. I keep my gasoline for my lawnmower in a 2.5 gallon plastic gasoline jug, and it goes 3-4 months without being used all winter. My mower runs on it just fine; I've had 4 mows this year so far, and I'm still running on gasoline I got last September. --Jayron32 03:51, 14 April 2012 (UTC)

Thanks for all your answers. I will use it and see what happens. 86.137.136.167 (talk) 10:24, 14 April 2012 (UTC)

Old gasoline undergoes chemical reactions which form varnish or gum which plugs the small jet orifices in the carburetor. Engine makers warn against using old gasoline. There are chemicals (Sta-bil, a product used in the US) which can be added to the gasoline so that it will not form these gummy deposits when stored. See [3]. There are numerous Youtube videos on cleaning various small engine carbs. A US lawnmower repair shop I know charges about $120 to clean the carb, replace the plug, change the oil and sharpen the blade, on mowers which sell new for under $180. Some folks pour the mower gas in the car gas tank at the end of the season(I wouldn't do this with ancient gummy gasoline), then run the mower until the gasoline is used up, then squirt a bit of motor oil into the cylinder through the spark plug hole, then crank the engine to lube the cylinder and prevent rust. They start next season with fresh gasoline. Service stations might accept old gasoline. If old gummy gas was stored in a gas can, it may be a mistake to refill it with fresh gas and put it in the mower. An old gas can, like a gummy carb, could probably be cleaned with carb cleaner. Edison (talk) 01:05, 15 April 2012 (UTC)