Instead of transferring the wine to bottles after a few days leave It for about 10 days and let most of the sugar turn to alcohol and co2. The foam will go away and the wine will start to clear slightly.Then when you bottle it add a teaspoon of sugar, this way, you know that there is enough sugar in the wine to make it really fizzy but not so much that you need to worry about shards of glass in young children faces.
The amount of alcohol in the win. Depends on how much sugar you put in (the yeast will turn ALL of the sugar to alcohol over time no matter where you keep it (bucket or bottles). 2.5kg of sugar in 25 liters will produce a final alcohol of about 6% (can add or remove). The more alcohol you make the more harsh the taste will be, if you go much above 10% it will need to be stored for a while to mellow (maybe a year)
Don't put too many flower heads in as they have a high amount of natural yeast in them and can make the champagne taste bad(a lesson learnt a few years ago, I thought in my inexperience that it would make it taste more flowery, trust me it didn't
Never wash the flower heads as this will remove much of the fragrance (if cleaning, maybe you can add more?)
Flowers snow white with yellow pollen, best picked in the morning (when the pollen is rich, before it gets deteriorated by the heat of the sun we’ve been getting it or the bees nick it)
Put flowers in a cloth bag to submerge
You only need the florets themselves (too much stalk can add an unwanted bitterness to the brew). Remove them with a fork.
If you did not add yeast and fermentation has not started after 3 days then it is time to give the thing a kick-start with a packet of Champagne/wine yeast.
Some areas can be wild yeast deserts meaning your champagne will never ferment. If you do manage to capture a wild yeast you never know which yeast will get to work on your drinks. Each yeast works differently so you can be in for a lottery of flavours and alcohol strengths. The only way around that is to add your own yeast and champagne yeast is the best option; this has the added bonus of making your elderflower champagne alcoholic.
Don’t shake your elderflowers to get rid of the insects as you will be shaking off the pollen and therefore the floral flavour. Instead put them to one on newspaper and let the bugs walk off by themselves, don’t worry they will!
Adding boiling water onto the flowers will indeed kill off the wild yeast. This is exactly what you are looking for when you are adding yeast as you don’t want two yeasts competing.
Wild yeasts are uncontrollable (different temperature triggers); can start to spontaneously ferment when wild yeasts get to work. Some areas will have the wrong type of wild yeast which might get to work momentarily and then die off. Some areas might have no yeasts
Most recipes call for wild yeast however, this can be a bit of a Russian roulette way of brewing.
700g en 4.5L = 8% alcohol
Need to add the yeast, plus yeast nutrient at the start
Why vinegar?: Most wine naturally contains some acetic acid. However, since this recipe does not include a grape element, the vinegar may partly compensate (yeast nutrient, can't live just with sugar)
2 tablespoons is 50 ml and vinegar is 5% acetic acid so you would be adding 2.5 g of it to 4.5 litres, 0.5% per litre, which is not unusual. Personally I would omit it and include 1 litre of grape juice or 250 g minced sultanas which will improve the flavour and boost the alcohol content to 10%
Flowers don't have natural nutrients for a good fermentation, unlike grape juice, so yes it would be a very good idea to add some.
Bottling at sg 1010 will probably burst. 1000 is safe, providing that champagne bottles that weigh at least 800 g are used.
If using vinegar can't store for long (it will convert into vinegar)
It’s always a bit hit and miss with a hydrometer in my opinion. What I would do is measure the specific gravity (SG) right at beginning (before the yeast is added) and then measure the SG twice more during the ferment. By recording the SG at each stage you can calculate both how the fermentation is going and how much ABV you ended up with- the reason you can calculate the ABV is the SG will have dropped (and you’ll know by how much) and that is because the sugar has been replaced by C02 (most of which escaped into the air) and alcohol.
Smell flowers before picking
BTW I've found the conversion for grape juice concentrate to raisins or sultanas. You take the volume of the concentrate in ml and divide by 1.2 and that gives you the weight of dried fruit in grams. So for this recipe you would replace the 150ml of concentrate with 125g of chopped raisins or sultanas.
As for exploding bottles, the best way to avoid this is to use sound champagne type bottles weighing at least 800g and ensuring that the wine has a specific gravity no higher than 1005 when put in the bottles with an airspace of at least 1.5 inches below the stopper. to act as a buffer. The pressure in the bottles increases with a rise in temperature so they must be stored somewhere cool, 15 c being the ideal, which is why a cellar is best.