Plastic Soda Bottles and the Sodastream: What to Know

Bottle sizes

To keep fill levels right, Dave Arnold stocks soda bottles in several sizes: 2 litres, 1.5 litres, 1 litre, 20 ounces (591.5 ml), 16.9 ounces (500 ml, which Poland Spring makes) and 12 ounces (354.9 ml, hard to find, though Coke makes some). The 2-litre bottles are for large events where a lot is poured quickly, though the sloshing when pouring from one makes him wince. At the bar he uses 1-litre bottles. The small 16.9- and 12-ounce bottles are handy for recipe testing, since they carbonate a single drink. The downsides: recycled plastic bottles look unsexy behind the bar, and the carbonation cycle is too slow to make single drinks to order. Still, he calls it the best system there is.

Plastic soda bottles

Soda bottles are made of polyethylene terephthalate, PET (or PETE), the most common polyester, the stuff of leisure suits. PET soda bottles are cheap and flexible and handle carbonation pressures easily. Bottles for still drinks cannot: he has had them blow up. There is no real danger, but it is embarrassing, he says, picturing a small chef’s office with a chest-high line of carbonated iced coffee sprayed around the walls.

• Even carbonation bottles are not indestructible. Do not put chunks of dry ice or liquid nitrogen in them, because they will blow up, and no boiling liquids, which deform them.
• Over a long time PET picks up aromas and colours from what it holds, so avoid root-beer and orange-soda bottles.
• Carbonator caps are meant to fit any standard soda bottle up to 2 litres, but the soda industry introduced a shorter cap style, which saves plastic but fits carbonator caps less well. They still work, but get the old style bottles if you can.

The lifetime of a PET bottle of soda is measured in weeks before it starts tasting flat.

Unlike glass, a perfect gas barrier, PET is semipermeable, and most gas leaks straight through the walls. So do not stock up on plastic-bottled soda for months in the pantry. The smaller the bottle, the more surface per volume and the faster it goes flat, which is why bars buy tiny glass bottles of soda. To store a home-carbonated drink for long, fluff the bottle with CO2 about once a week.

A newer bottle has layers of PET and polyvinyl alcohol (PVA), a much better gas barrier that breaks down harmlessly in recycling, so it stays recyclable and holds carbonation much better, but it carries only the ordinary PET recycling code, so you cannot tell which you have. On safety he notes that in 2011 only 29 percent of PET bottles were recycled (EPA data), with the rate rising. The industry’s trade group (NAPCOR) insists PET is safe to reuse, freeze and store in, that nothing leaches, that it contains no bisphenol A, and that the phthalate in its name is not the worrying kind. He says it is up to you whether to believe a group whose only job is supporting PET. He has drunk from PET all his life and serves his family drinks made in it, and will keep doing so until he hears credible safety concerns, without claiming certainty.

Technique two: the Sodastream

The Sodastream has revolutionised home carbonation. The maker warns against carbonating anything but pure water, but you can with care. With water it is very simple: fill the special bottle to the line with cold water, screw it into the machine and press the button until the machine breaks wind. No shaking and no purging of the headspace are needed. A carbonator wand just below the surface injects CO2, making zillions of tiny bubbles and so ample surface area; meanwhile CO2 pushes up into the headspace, and when the pressure exceeds the factory-set carbonation pressure a relief valve opens and pushes the air out. You cannot change the pressure, but it gives adequate carbonation for most cocktails.

The trouble with cocktails is foam. Foam can clog the relief valve, and the resulting pressure can damage the machine or, if the bottle ruptures or flies out, anything nearby. The trick with wine or cocktails is never to let the foam reach the top of the bottle. The rest of the method is in the article on carbonating at home.