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1. After primary fermentation was complete I tasted a little when racking and the mead wasn't very sweet. Do I simply add more raw honey to sweeten it and if so how to I stop it from fermenting again?
you either keep feeding it small amounts of honey, until it can't ferment any further (called "step feeding"), or you hit it with wine stabiliser and crushed campden tablets (Melvin at Johnsons Homebrew in Worthing has both), then you back sweeten it to taste - if I intend using honey to back sweeten, I usually stabilise my mead, then take a reading, then sweeten it to about 1.010 - 1.015 (about medium sweet). I do that when it's cloudy/uncleared as using honey (my preference) can cause a haze in a cleared mead and it's a PITA to have to clear it twice, so I back sweeten then sort the clearing and only have to do that once.
2. I want to bottle the mead and make it fizzy. Will beer bottles be fine because I have read that only champagne bottles can withstand the pressure?
Yes, you can use beer bottles, but you can't really get as high a pressure as you would with champagne/sparkling wines, because of the pressure issue you've already highlighted.
3. Now that my mead has been standing for about a week in temperatures of around 5C or 41F (in a carbuoy in the garage), will the yeast have died or will it start to ferment when I add sweetening honey and bottle? Can further yeast be added at this stage or is it not recommended?
Not necessarily, the drop in temps will have helped some of the yeast to drop out of suspension, but even with cleared meads (or wines) there's still some yeast cells in it. So without stabilisation, it's entirely possible for you to back sweeten now, while it's cool, but then end up with bottle bombs, while the weather warms up.
Adding more yeast isn't necessarily an issue, but it's often only done for "methode champenoise" to carbonate sparkling wines - and a lot of the kit needed for that is out of the homebrewers price range (I've seen it done, both at Bolney and at the vineyard between Ditchling and Wivelsfield). The issue is removing the yeast for "commercial" reasons. If it's just you, family and friends drinking it, then it might be less of a problem.
4. I read about the process of pasteurisation for cider where you add sugars to restart fermentation when bottling, sample the bottles over a few days to check pressure and then put bottles in a pan of hot water to kill the yeast when ready. Do you think this could work for mead?
That's a new one on me, it's certainly not pasteurisation. You've described a bit of a "mish mash" of techniques there. Pasteurisation might be used on straight apple juice, but that's usually for "shelf life" reasons and to destroy any yeasts found naturally on apples, to prevent the juice fermenting.
Here's the link for how "methode champenoise" is done (well it's wikipedia, but close enough). You certainly wouldn't use heat on bottled sparkling/fizzy drinks as it could cause the CO2 to come out of solution much quicker, potentially creating bottle bombs, at least possibly popping the caps off...
5. Also, just as a general question what are the highest and lowest temperatures yeast can withstand?
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One of the reasons I moved to getting Lalvin yeasts mail order, is because Lallemand publish more info/data about them, than any other manufacturer (
here's a good example of that).
From that data, you can work out what yeast you want to use, or whether you need some sort of temperature control for the fermentation. A good example, is D47 yeast. It seems popular with people both here, and
over at Gotmead. But, closer inspection of the data, shows that it has a very narrow temperature range - not necessarily a problem, but if it's fermented too warm i.e. above about 68F/20C, it's known to produce higher levels of fusels in the ferment, which either take a hell of a long time to age out, if at all. Medsen Fey (both here and over at GM) is in Florida, so has temperature issues at some times of the year. He uses "paint thinners" as a good analogy.
It also happens that one of the good yeasts for mead is Lalvin K1V-1116, which is also packaged by Muntons as Gervin brand Varietal "E" (but a lot of the home brew shops still don't keep it, and no, Melvin over at Johnsons home brew in Worthing doesn't keep either, the Lalvin or the Gervin versions).
The other reason I moved to using the Lalvin yeasts, is because they're popular here and at GM, means its much easier to copy a recipe as closely as possible - actually, its often the honeys that are harder to source. They have a much bigger choice than we do here. I use
Paynes in Hurstpierpoint if I can, as they have some choice, not as wide as I'd like but better than nothing. Dunno if there's anything over your way or not, haven't really looked (I'm over by Shoreham, hence the local references)......
{edit}p.s. Oh and if you have a look into it, you'll see why it is, that most champagnes/sparkling wines are dry. Because making sweet ones bubbly, is basically down for forced carbonation, where you'd need a cornelius keg a.k.a. corny keg and a source of carbon dioxide to pressurise the keg enough to dispense it, but also to make it bubbly - I'd guess that if you could get the keg cold enough, you could then get the mead transferred to champagne/sparkling wine bottles and retain enough carbonation - you still have to get the stoppers/bungs in the bottle and get them wired down to keep them in place........ which is why "bottle priming" with dry meads/wines is done with home brewing, because it's easier/cheaper, but you still might end up with a little sediment in the bottle{/edit}
Hope that helps some.....