Most people who make soy milk at home run into the same thing. The routine is right, the beans are good, the milk strains clean, and the glass still carries a grassy, slightly bitter edge that the carton from the shop does not have. People call it beany. It is a specific flavor with a specific cause, and part of that cause is air.
Where the beany flavor comes from
Soybeans carry an enzyme called lipoxygenase. Inside an intact bean it sits apart from the fats it acts on. Grinding the bean brings them together, and when oxygen is present the enzyme turns those fats into small volatile compounds. One of the best known is hexanal, which is also a large part of the smell of cut grass. Those compounds are what you are tasting.
Commercial soy milk avoids most of this with heat. Blanching or hot grinding inactivates the enzyme before it has much chance to work. At home the beans are usually soaked cold and ground cold, so the enzyme is fully active at exactly the moment the beans are broken open.
Why a blender makes it worse
A blender tears the whole batch of beans open at once, and while it does so it drags air down through the vortex and folds it through the slurry. Maximum enzyme release and maximum oxygen contact arrive together, with friction heat on top.
Soy protein also foams readily. The head of foam on top of freshly blended soy milk is air the blades whipped in, held in place by the protein. It slows the straining, it clogs the bag, and every bubble in it is holding oxygen against freshly ground bean.
What taking the air out changes
A vacuum lid pumps most of the air out of the sealed jar before the blades spin, and the seal holds while the motor runs. The enzyme is still there and the fats are still there. The oxygen it needs is largely gone during the grind, which is when the reaction would otherwise run hardest.
Two things follow that you can see and taste without instruments. There is very little foam, so the milk strains through the bag without fighting it. And the grassy edge is quieter, because less of the reaction ran while the beans were being ground.
We have not measured how much less. The chemistry is well established and the direction is not in doubt, but a figure for your beans, your soak and your ratio would be invented, so we do not give one.
What it does not change
Removing the air does not remove the enzyme. Soy milk still has to be cooked after grinding, both to finish inactivating it and because raw soy is not something to drink. Heat the strained milk on the stove as you normally would. Do not put hot liquid into the jar and do not try to cook in it; the lid is for the grind, not the pot.
It also does not fix beans that were stale or under soaked, and it does not change the ratio of water to beans, which does more for body than anything else here.
A routine that works
- Soak dry soybeans overnight in plenty of cold water. Rinse until the water runs clear.
- Load the jar with the beans and cold water. A ratio around one part beans to five or six parts water by volume is a common starting point; adjust for the body you like.
- Seat the lid, pick a preset and press Go. When the screen says Ready to Blend, switch the lid off, then blend until smooth.
- Pull the red tab to vent, open, and strain through a nut milk bag. Without the foam this is quick.
- Cook the strained milk on the stove as your soy milk recipe directs. Raw soy milk has to be boiled; the vacuum lid changes the grind, not the cooking. Cool, and keep it refrigerated.
Which VOID fits the blender you own
The Complete System is our vacuum blender. If you already own a Blendtec or a classic Vitamix, we make a VOID lid and a Retrofit Kit for those too. The lid on its own seats on Blendtec WildSide+, WildSide and Fourside jars, and on the Professional 800. A classic Vitamix, the kind with a black rubber pad with grooves on the base, takes the Retrofit Kit, which brings a VOID jar that seats on your base. The smooth Ascent and Venturist bases do not take it, and for those, or for a kitchen with no blender yet, the Complete System is a full blender with the lid in the box.
Pick your blender below and it tells you which one to order. On US orders, if it does not fit your machine, the return is free.
